From d746752ba0b065439482ea45fcbe0814cada4d92 Mon Sep 17 00:00:00 2001
From: stefaandesmet2003 <stefaandesmet2003@yahoo.co.uk>
Date: Tue, 9 Jan 2018 00:07:48 +0100
Subject: [PATCH 01/14] working code for sigma delta generator

provide a simple interface to attach/detach pins to the sigma-delta generator, and get/set the 2 parameters prescaler & target
---
 cores/esp8266/core_esp8266_sigma_delta.c | 154 +++++++++++++++++++++++
 cores/esp8266/sigma_delta.h              | 107 +++++++++++++++-
 2 files changed, 256 insertions(+), 5 deletions(-)
 create mode 100644 cores/esp8266/core_esp8266_sigma_delta.c

diff --git a/cores/esp8266/core_esp8266_sigma_delta.c b/cores/esp8266/core_esp8266_sigma_delta.c
new file mode 100644
index 0000000000..eaa0dc483a
--- /dev/null
+++ b/cores/esp8266/core_esp8266_sigma_delta.c
@@ -0,0 +1,154 @@
+/*
+/******************************************************************************
+ * Sigma delta module
+
+This module controls the esp8266 internal sigma delta source
+Each pin can be connected to the sigma delta source
+The target duty and frequency can be modified via the register GPIO_SIGMA_DELTA
+
+THE TARGET FREQUENCY IS DEFINED AS:
+
+FREQ = 80,000,000/prescaler * target /256  HZ,     0<target<128
+FREQ = 80,000,000/prescaler * (256-target) /256  HZ,     128<target<256
+target: duty ,0-255
+prescaler: clk_div,0-255
+so the target and prescale will both affect the freq.
+
+Usage :
+1. sigma_delta_enable() : activate the sigma delta source with default prescalar (0) & target (0)
+2. sigma_delta_attachPin(pin), any pin 0..15, TBC if gpio16 supports sigma-delta source
+     This will set the pin to NORMAL output mode (pinMode(pin,OUTPUT))
+3. sigma_delta_setPrescaler(uint8_t) : reduce the output frequencies
+4. sigma_delta_setTarget(uint8_t) : set the output signal duty cycle, duty cycle = target/256
+
+5. sigma_delta_detachPin(pin), this will revert the pin to NORMAL output mode & GPIO source. 
+The sigma delta source remains on until :
+6. sigma_delta_disable()
+
+*******************************************************************************/
+
+#include "Arduino.h" // using pinMode
+
+// definitions in esp8266_peri.h style
+#define GPSD  ESP8266_REG(0x368) // GPIO_SIGMA_DELTA register @ 0x600000368
+#define GPSDT 0  // target, 8 bits
+#define GPSDP 8  // prescaler, 8 bits
+#define GPSDE 16 // enable
+
+/******************************************************************************
+ * FunctionName : sigma_delta_start
+ * Description  : enable the internal sigma delta source
+ * Parameters   : none
+ * Returns      : none
+*******************************************************************************/
+void ICACHE_FLASH_ATTR sigma_delta_enable()
+{
+  GPSD = (0 << GPSDT) | (0 << GPSDP) | (1 << GPSDE); //SIGMA_DELTA_TARGET(0) | SIGMA_DELTA_PRESCALER(0) | SIGMA_DELTA_ENABLE(ENABLED)
+}
+
+/******************************************************************************
+ * FunctionName : sigma_delta_disable
+ * Description  : stop the internal sigma delta source
+ * Parameters   : none
+ * Returns      : none
+*******************************************************************************/
+void ICACHE_FLASH_ATTR sigma_delta_disable()
+{
+  GPSD = (0 << GPSDT) | (0 << GPSDP) | (0 << GPSDE); //SIGMA_DELTA_TARGET(0) | SIGMA_DELTA_PRESCALER(0) | SIGMA_DELTA_ENABLE(DISABLED)
+}
+
+/******************************************************************************
+ * FunctionName : sigma_delta_attachPin
+ * Description  : connects the sigma delta source to a physical output pin
+ * Parameters   : pin (0..15)
+ * Returns      : none
+*******************************************************************************/
+void ICACHE_FLASH_ATTR sigma_delta_attachPin(uint8_t pin)
+{
+  // make the chosen pin an output pin
+  pinMode (pin, OUTPUT);
+  if (pin < 16) {
+    // set its source to the sigma delta source
+    GPC(pin) |= (1 << GPCS); //SOURCE 0:GPIO_DATA,1:SigmaDelta
+  }
+}
+
+/******************************************************************************
+ * FunctionName : sigma_delta_detachPin
+ * Description  : disconnects the sigma delta source from a physical output pin
+ * Parameters   : pin (0..16)
+ * Returns      : none
+*******************************************************************************/
+void ICACHE_FLASH_ATTR sigma_delta_detachPin(uint8_t pin)
+{
+  if (pin < 16) {
+    // set its source to the sigma delta source
+    GPC(pin) &=  ~(1 << GPCS); //SOURCE 0:GPIO_DATA,1:SigmaDelta
+  }
+}
+
+/******************************************************************************
+ * FunctionName : sigma_delta_isPinAttached
+ * Description  : query if pin is attached
+ * Parameters   : pin (0..16)
+ * Returns      : bool
+*******************************************************************************/
+bool ICACHE_FLASH_ATTR sigma_delta_isPinAttached(uint8_t pin)
+{
+  if (pin < 16) {
+    // set its source to the sigma delta source
+     return (GPC(pin) & (1 << GPCS)); //SOURCE 0:GPIO_DATA,1:SigmaDelta
+  }
+  else
+    return false;
+}
+
+/******************************************************************************
+ * FunctionName : sigma_delta_getTarget
+ * Description  : get the target value from the GPIO_SIGMA_DELTA register
+ * Parameters   : none
+ * Returns      : uint8_t target value 0..255
+*******************************************************************************/
+uint8_t ICACHE_FLASH_ATTR sigma_delta_getTarget(void)
+{
+  return (uint8_t)((GPSD >> GPSDT) & 0xFF);
+}
+
+/******************************************************************************
+ * FunctionName : sigma_delta_setTarget
+ * Description  : set the target (duty cycle) for the sigma-delta source
+ * Parameters   : uint8 target, 0-255, duty cycle = target/256
+ * Returns      : none
+*******************************************************************************/
+void ICACHE_FLASH_ATTR sigma_delta_setTarget(uint8_t target)
+{
+  uint32_t reg = GPSD;
+
+  reg = (reg & ~(0xFF << GPSDT)) | ((target & 0xFF) << GPSDT);
+  GPSD = reg;
+}
+
+/******************************************************************************
+ * FunctionName : sigma_delta_getPrescaler
+ * Description  : get the prescaler value from the GPIO_SIGMA_DELTA register
+ * Parameters   : none
+ * Returns      : uint8 prescaler, CLK_DIV , 0-255
+*******************************************************************************/
+uint8_t ICACHE_FLASH_ATTR sigma_delta_getPrescaler(uint8_t prescaler)
+{
+  return (uint8_t)((GPSD >> GPSDP) & 0xFF);
+}
+
+/******************************************************************************
+ * FunctionName : sigma_delta_setPrescaler
+ * Description  : set the clock divider for the sigma-delta source
+ * Parameters   : uint8 prescaler, 0-255, divides the 80MHz base clock by this amount
+ * Returns      : none
+*******************************************************************************/
+void ICACHE_FLASH_ATTR sigma_delta_setPrescaler(uint8_t prescaler)
+{
+  uint32_t reg = GPSD;
+
+  reg = (reg & ~(0xFF << GPSDP)) | ((prescaler & 0xFF) << GPSDP);
+  GPSD = reg;
+}
diff --git a/cores/esp8266/sigma_delta.h b/cores/esp8266/sigma_delta.h
index 2e8bdc092f..3af2ac8080 100644
--- a/cores/esp8266/sigma_delta.h
+++ b/cores/esp8266/sigma_delta.h
@@ -18,15 +18,112 @@
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
+ 
+ /*
+/******************************************************************************
+ * Info Sigma delta module
+
+This module controls the esp8266 internal sigma delta source
+Each pin can be connected to the sigma delta source
+The target duty and frequency can be modified via the register GPIO_SIGMA_DELTA
+
+THE TARGET FREQUENCY IS DEFINED AS:
+
+FREQ = 80,000,000/prescaler * target /256  HZ,     0<target<128
+FREQ = 80,000,000/prescaler * (256-target) /256  HZ,     128<target<256
+target: duty ,0-255
+prescaler: clk_div,0-255
+so the target and prescale will both affect the freq.
+
+Usage :
+1. sigma_delta_enable() : activate the sigma delta source with default prescalar (0) & target (0)
+2. sigma_delta_attachPin(pin), any pin 0..15, TBC if gpio16 supports sigma-delta source
+     This will set the pin to NORMAL output mode (pinMode(pin,OUTPUT))
+3. sigma_delta_setPrescaler(uint8_t) : reduce the output frequencies
+4. sigma_delta_setTarget(uint8_t) : set the output signal duty cycle, duty cycle = target/256
+
+5. sigma_delta_detachPin(pin), this will revert the pin to NORMAL output mode & GPIO source. 
+The sigma delta source remains on until :
+6. sigma_delta_disable()
+
+copy this code as example :
+
+#include "sigma_delta.h"
+
+void setup() {
+
+  Serial.begin(115200);
+  pinMode(BUILTIN_LED,OUTPUT); // blinkie & sigma-delta mix
+  
+  uint32 pin = 4; //D2
+  sigma_delta_enable();
+  //sigma_delta_disable();
+  sigma_delta_attachPin(BUILTIN_LED);
+  sigma_delta_attachPin(4); // D2
+  
+  sigma_delta_setPrescaler(255);
+
+  Serial.println();
+  Serial.println("Start Sigma Delta Example\n");
+  Serial.println("Attached gpio4 to the sigma delta source\n");
+  Serial.printf("Current target = %i, prescaler = %i\n",sigma_delta_getTarget(),sigma_delta_getPrescaler());
+}
+
+void loop() {
+ 
+  uint8_t target, iRepeat;
+  
+  Serial.println("Attaching the built in led to the sigma delta source now\n");
+  Serial.printf("Current target = %i, prescaler = %i\n",sigma_delta_getTarget(),sigma_delta_getPrescaler());
+  sigma_delta_attachPin(BUILTIN_LED);
+  
+  Serial.println("dimming builtin led...\n");
+  for (iRepeat=0;iRepeat<10;iRepeat++)
+  {
+    for (target=0; target<255;target=target+5)
+    {
+      sigma_delta_setTarget(target);
+      delay(10);
+    }
+    
+    for (target=255; target>0;target=target-5)
+    {
+      sigma_delta_setTarget(target);
+      delay(10);
+    }
+    
+  }
+  Serial.println("detaching builtin led & playing a blinkie\n");
+  sigma_delta_detachPin(BUILTIN_LED);
+  for (iRepeat=0;iRepeat<20;iRepeat++)
+  {
+    digitalWrite(BUILTIN_LED,!digitalRead(BUILTIN_LED));
+    delay(500);
+  }
+    
+}
+
+*******************************************************************************/
 
 #ifndef SIGMA_DELTA_H
 #define SIGMA_DELTA_H
 
-#include <stdint.h>
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void sigma_delta_enable(void);
+void sigma_delta_disable(void);
+void sigma_delta_attachPin(uint8_t pin);
+void sigma_delta_detachPin(uint8_t pin);
+bool sigma_delta_isPinAttached(uint8_t pin);
+uint8_t sigma_delta_getTarget(void);
+void sigma_delta_setTarget(uint8_t target);
+uint8_t sigma_delta_getPrescaler(void);
+void sigma_delta_setPrescaler(uint8_t prescaler);
 
-void sigma_delta_close(uint32_t gpio);
-void set_sigma_target(uint8_t target);
-void set_sigma_prescale(uint8_t prescale);
-void set_sigma_duty_312KHz(uint8_t duty);
+#ifdef __cplusplus
+}
+#endif
 
 #endif//SIGMA_DELTA_H

From 85b932343abf42b0bb1c582cccd034f631b57446 Mon Sep 17 00:00:00 2001
From: stefaandesmet2003 <stefaandesmet2003@yahoo.co.uk>
Date: Thu, 11 Jan 2018 00:08:54 +0100
Subject: [PATCH 02/14] removed example code from header file

---
 sigma_delta.h | 72 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 sigma_delta.h

diff --git a/sigma_delta.h b/sigma_delta.h
new file mode 100644
index 0000000000..6ed66191d5
--- /dev/null
+++ b/sigma_delta.h
@@ -0,0 +1,72 @@
+/* 
+ sigma_delta.h - esp8266 sigma-delta source
+
+ Copyright (c) 2014 Ivan Grokhotkov. All rights reserved.
+ This file is part of the esp8266 core for Arduino environment.
+ 
+ This library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ This library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with this library; if not, write to the Free Software
+ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+ 
+ /*
+/******************************************************************************
+ * Info Sigma delta module
+
+This module controls the esp8266 internal sigma delta source
+Each pin can be connected to the sigma delta source
+The target duty and frequency can be modified via the register GPIO_SIGMA_DELTA
+
+THE TARGET FREQUENCY IS DEFINED AS:
+
+FREQ = 80,000,000/prescaler * target /256  HZ,     0<target<128
+FREQ = 80,000,000/prescaler * (256-target) /256  HZ,     128<target<256
+target: duty ,0-255
+prescaler: clk_div,0-255
+so the target and prescale will both affect the freq.
+
+Usage :
+1. sigma_delta_enable() : activate the sigma delta source with default prescalar (0) & target (0)
+2. sigma_delta_attachPin(pin), any pin 0..15, TBC if gpio16 supports sigma-delta source
+     This will set the pin to NORMAL output mode (pinMode(pin,OUTPUT))
+3. sigma_delta_setPrescaler(uint8_t) : reduce the output frequencies
+4. sigma_delta_setTarget(uint8_t) : set the output signal duty cycle, duty cycle = target/256
+
+5. sigma_delta_detachPin(pin), this will revert the pin to NORMAL output mode & GPIO source. 
+The sigma delta source remains on until :
+6. sigma_delta_disable()
+
+*******************************************************************************/
+
+#ifndef SIGMA_DELTA_H
+#define SIGMA_DELTA_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void sigma_delta_enable(void);
+void sigma_delta_disable(void);
+void sigma_delta_attachPin(uint8_t pin);
+void sigma_delta_detachPin(uint8_t pin);
+bool sigma_delta_isPinAttached(uint8_t pin);
+uint8_t sigma_delta_getTarget(void);
+void sigma_delta_setTarget(uint8_t target);
+uint8_t sigma_delta_getPrescaler(void);
+void sigma_delta_setPrescaler(uint8_t prescaler);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif//SIGMA_DELTA_H

From 648483c8261db5cc3e6c2b33f104ffc0bfd70adf Mon Sep 17 00:00:00 2001
From: stefaandesmet2003 <stefaandesmet2003@yahoo.co.uk>
Date: Thu, 11 Jan 2018 00:14:17 +0100
Subject: [PATCH 03/14] example for the esp8266 sigma delta generator hardware

---
 .../SigmaDeltaDemo/SigmaDeltaDemo.ino         | 84 +++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino

diff --git a/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
new file mode 100644
index 0000000000..bc1390807f
--- /dev/null
+++ b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
@@ -0,0 +1,84 @@
+/*
+  Sigma Delta Generator example
+  
+  This example demonstrates the use of the ESP8266 internal hardware sigma delta source.
+  Each GPIO pin or multiple pins can be connected to the one sigma delta source.
+  THE sigma delta output frequency is defined by the ESP8266 hardware as:
+
+  FREQ = 80,000,000/prescaler * target /256  HZ,          0<target<128
+  FREQ = 80,000,000/prescaler * (256-target) /256  HZ,    128<target<256
+  with :
+  target: 0-255, defines the 8-bit duty cycle of the output signal, , duty cycle = target/256
+  prescaler: 0-255, reduce the output frequencies
+  
+  so both the target and prescaler will affect the freq.
+  
+  Differences with Arduino library analogWrite :
+  - the arduino analogWrite pwm uses a hardware timer and ISR to generate the pwm signal. The sigma delta pwm doesn't need a hardware timer. 
+    The FRC1 timer can then be used for other purposes.
+  - the arduino analogWrite pwm produces a more or less fixed frequency around 900Hz. The sigma delta source produces a variable output frequency, 
+    that depends on the duty cycle. Example, with prescaler = 10, the output frequency varies between 31,kHz and 4MHz
+  - the sigma delta source produces much higher frequencies. This allows the output to be easily smoothed by a RC-filter and realise a decent 8-bit DAC
+  - the arduino analogWrite pwm has a higher resolution, default 12-bit, and up to 16-bit resolution. The sigma delta source has only 8-bit resolution
+    
+  The example doesn't require additional hardware.
+  
+  With an RC-filter (for example R=17k & C=100nF), a 'DC' output signal can be obtained with voltage between 0 and 3.3V
+  For higher value capacitors, it might be necessary to add a high-speed buffer between the esp8266 output and RC-filter to limit the current ac load on the 
+  pin output driver.
+
+*/
+#include "sigma_delta.h"
+
+void setup() {
+
+  Serial.begin(115200);
+  pinMode(BUILTIN_LED,OUTPUT); // blinkie & sigma-delta mix
+  
+  uint32 pin = 4; //D2
+  sigma_delta_enable();
+  //sigma_delta_disable();
+  sigma_delta_attachPin(BUILTIN_LED);
+  sigma_delta_attachPin(4); // D2
+  
+  sigma_delta_setPrescaler(255);
+
+  Serial.println();
+  Serial.println("Start Sigma Delta Example\n");
+  Serial.println("Attached gpio4 to the sigma delta source\n");
+  Serial.printf("Current target = %i, prescaler = %i\n",sigma_delta_getTarget(),sigma_delta_getPrescaler());
+}
+
+void loop() {
+ 
+  uint8_t target, iRepeat;
+  
+  Serial.println("Attaching the built in led to the sigma delta source now\n");
+  Serial.printf("Current target = %i, prescaler = %i\n",sigma_delta_getTarget(),sigma_delta_getPrescaler());
+  sigma_delta_attachPin(BUILTIN_LED);
+  
+  Serial.println("dimming builtin led...\n");
+  for (iRepeat=0;iRepeat<10;iRepeat++)
+  {
+    for (target=0; target<255;target=target+5)
+    {
+      sigma_delta_setTarget(target);
+      delay(10);
+    }
+    
+    for (target=255; target>0;target=target-5)
+    {
+      sigma_delta_setTarget(target);
+      delay(10);
+    }
+    
+  }
+  Serial.println("detaching builtin led & playing a blinkie\n");
+  sigma_delta_detachPin(BUILTIN_LED);
+  for (iRepeat=0;iRepeat<20;iRepeat++)
+  {
+    digitalWrite(BUILTIN_LED,!digitalRead(BUILTIN_LED));
+    delay(500);
+  }
+    
+}

From c5351a0877519a16bcd1d7d62d9a3be0b37ae38c Mon Sep 17 00:00:00 2001
From: stefaandesmet2003 <stefaandesmet2003@yahoo.co.uk>
Date: Tue, 23 Jan 2018 21:51:40 +0100
Subject: [PATCH 04/14] modified interface in line with ESP32 implementation

---
 cores/esp8266/core_esp8266_sigma_delta.c | 114 +++++++++++------------
 cores/esp8266/sigma_delta.h              |  96 ++++---------------
 2 files changed, 76 insertions(+), 134 deletions(-)

diff --git a/cores/esp8266/core_esp8266_sigma_delta.c b/cores/esp8266/core_esp8266_sigma_delta.c
index eaa0dc483a..37d1fca33d 100644
--- a/cores/esp8266/core_esp8266_sigma_delta.c
+++ b/cores/esp8266/core_esp8266_sigma_delta.c
@@ -1,32 +1,3 @@
-/*
-/******************************************************************************
- * Sigma delta module
-
-This module controls the esp8266 internal sigma delta source
-Each pin can be connected to the sigma delta source
-The target duty and frequency can be modified via the register GPIO_SIGMA_DELTA
-
-THE TARGET FREQUENCY IS DEFINED AS:
-
-FREQ = 80,000,000/prescaler * target /256  HZ,     0<target<128
-FREQ = 80,000,000/prescaler * (256-target) /256  HZ,     128<target<256
-target: duty ,0-255
-prescaler: clk_div,0-255
-so the target and prescale will both affect the freq.
-
-Usage :
-1. sigma_delta_enable() : activate the sigma delta source with default prescalar (0) & target (0)
-2. sigma_delta_attachPin(pin), any pin 0..15, TBC if gpio16 supports sigma-delta source
-     This will set the pin to NORMAL output mode (pinMode(pin,OUTPUT))
-3. sigma_delta_setPrescaler(uint8_t) : reduce the output frequencies
-4. sigma_delta_setTarget(uint8_t) : set the output signal duty cycle, duty cycle = target/256
-
-5. sigma_delta_detachPin(pin), this will revert the pin to NORMAL output mode & GPIO source. 
-The sigma delta source remains on until :
-6. sigma_delta_disable()
-
-*******************************************************************************/
-
 #include "Arduino.h" // using pinMode
 
 // definitions in esp8266_peri.h style
@@ -36,23 +7,23 @@ The sigma delta source remains on until :
 #define GPSDE 16 // enable
 
 /******************************************************************************
- * FunctionName : sigma_delta_start
+ * FunctionName : sigmaDeltaEnable
  * Description  : enable the internal sigma delta source
  * Parameters   : none
  * Returns      : none
 *******************************************************************************/
-void ICACHE_FLASH_ATTR sigma_delta_enable()
+void ICACHE_FLASH_ATTR sigmaDeltaEnable()
 {
   GPSD = (0 << GPSDT) | (0 << GPSDP) | (1 << GPSDE); //SIGMA_DELTA_TARGET(0) | SIGMA_DELTA_PRESCALER(0) | SIGMA_DELTA_ENABLE(ENABLED)
 }
 
 /******************************************************************************
- * FunctionName : sigma_delta_disable
+ * FunctionName : sigmaDeltaDisable
  * Description  : stop the internal sigma delta source
  * Parameters   : none
  * Returns      : none
 *******************************************************************************/
-void ICACHE_FLASH_ATTR sigma_delta_disable()
+void ICACHE_FLASH_ATTR sigmaDeltaDisable()
 {
   GPSD = (0 << GPSDT) | (0 << GPSDP) | (0 << GPSDE); //SIGMA_DELTA_TARGET(0) | SIGMA_DELTA_PRESCALER(0) | SIGMA_DELTA_ENABLE(DISABLED)
 }
@@ -60,11 +31,12 @@ void ICACHE_FLASH_ATTR sigma_delta_disable()
 /******************************************************************************
  * FunctionName : sigma_delta_attachPin
  * Description  : connects the sigma delta source to a physical output pin
- * Parameters   : pin (0..15)
+ * Parameters   : pin (0..15), channel = unused, for compatibility with ESP32
  * Returns      : none
 *******************************************************************************/
-void ICACHE_FLASH_ATTR sigma_delta_attachPin(uint8_t pin)
+void ICACHE_FLASH_ATTR sigmaDeltaAttachPin(uint8_t pin, uint8_t channel)
 {
+  (void) channel;
   // make the chosen pin an output pin
   pinMode (pin, OUTPUT);
   if (pin < 16) {
@@ -79,7 +51,7 @@ void ICACHE_FLASH_ATTR sigma_delta_attachPin(uint8_t pin)
  * Parameters   : pin (0..16)
  * Returns      : none
 *******************************************************************************/
-void ICACHE_FLASH_ATTR sigma_delta_detachPin(uint8_t pin)
+void ICACHE_FLASH_ATTR sigmaDeltaDetachPin(uint8_t pin)
 {
   if (pin < 16) {
     // set its source to the sigma delta source
@@ -88,12 +60,12 @@ void ICACHE_FLASH_ATTR sigma_delta_detachPin(uint8_t pin)
 }
 
 /******************************************************************************
- * FunctionName : sigma_delta_isPinAttached
+ * FunctionName : sigmaDeltaIsPinAttached
  * Description  : query if pin is attached
  * Parameters   : pin (0..16)
  * Returns      : bool
 *******************************************************************************/
-bool ICACHE_FLASH_ATTR sigma_delta_isPinAttached(uint8_t pin)
+bool ICACHE_FLASH_ATTR sigmaDeltaIsPinAttached(uint8_t pin)
 {
   if (pin < 16) {
     // set its source to the sigma delta source
@@ -104,51 +76,77 @@ bool ICACHE_FLASH_ATTR sigma_delta_isPinAttached(uint8_t pin)
 }
 
 /******************************************************************************
- * FunctionName : sigma_delta_getTarget
- * Description  : get the target value from the GPIO_SIGMA_DELTA register
- * Parameters   : none
- * Returns      : uint8_t target value 0..255
+ * FunctionName : sigmaDeltaSetup
+ * Description  : start the sigma delta generator with the chosen parameters
+ * Parameters   : channel = unused (for compatibility with ESP32), 
+ *                freq : 1220-312500 (lowest frequency in the output signal's spectrum)
+ * Returns      : uint32_t the actual frequency, closest to the input parameter
 *******************************************************************************/
-uint8_t ICACHE_FLASH_ATTR sigma_delta_getTarget(void)
+uint32_t ICACHE_FLASH_ATTR sigmaDeltaSetup(uint8_t channel, uint32_t freq)
 {
-  return (uint8_t)((GPSD >> GPSDT) & 0xFF);
+  (void) channel;
+  
+  uint32_t prescaler = ((uint32_t)10000000/(freq*32)) - 1;
+  
+  if(prescaler > 0xFF) {
+      prescaler = 0xFF;
+  }
+  sigmaDeltaEnable();
+  sigmaDeltaSetPrescaler ((uint8_t) prescaler);
+  //sigmaDeltaSetTarget ((uint8_t) 0x80); // 50% duty cycle
+  
+  return 10000000/((prescaler + 1) * 32);
 }
 
 /******************************************************************************
- * FunctionName : sigma_delta_setTarget
- * Description  : set the target (duty cycle) for the sigma-delta source
- * Parameters   : uint8 target, 0-255, duty cycle = target/256
+ * FunctionName : sigmaDeltaWrite
+ * Description  : set the duty cycle for the sigma-delta source
+ * Parameters   : uint8 duty, 0-255, duty cycle = target/256, 
+ *                channel = unused, for compatibility with ESP32
  * Returns      : none
 *******************************************************************************/
-void ICACHE_FLASH_ATTR sigma_delta_setTarget(uint8_t target)
+void ICACHE_FLASH_ATTR sigmaDeltaWrite(uint8_t channel, uint8_t duty)
 {
   uint32_t reg = GPSD;
+  (void) channel;
 
-  reg = (reg & ~(0xFF << GPSDT)) | ((target & 0xFF) << GPSDT);
+  reg = (reg & ~(0xFF << GPSDT)) | ((duty & 0xFF) << GPSDT);
   GPSD = reg;
+  
 }
-
 /******************************************************************************
- * FunctionName : sigma_delta_getPrescaler
- * Description  : get the prescaler value from the GPIO_SIGMA_DELTA register
- * Parameters   : none
- * Returns      : uint8 prescaler, CLK_DIV , 0-255
+ * FunctionName : sigmaDeltaRead
+ * Description  : set the duty cycle for the sigma-delta source
+ * Parameters   : none, channel = unused, for compatibility with ESP32
+ * Returns      : uint8_t duty cycle value 0..255
 *******************************************************************************/
-uint8_t ICACHE_FLASH_ATTR sigma_delta_getPrescaler(uint8_t prescaler)
+uint8_t ICACHE_FLASH_ATTR sigmaDeltaRead(uint8_t channel)
 {
-  return (uint8_t)((GPSD >> GPSDP) & 0xFF);
+  (void) channel;
+  return (uint8_t)((GPSD >> GPSDT) & 0xFF);
 }
 
 /******************************************************************************
- * FunctionName : sigma_delta_setPrescaler
+ * FunctionName : sigmaDeltaSetPrescaler
  * Description  : set the clock divider for the sigma-delta source
  * Parameters   : uint8 prescaler, 0-255, divides the 80MHz base clock by this amount
  * Returns      : none
 *******************************************************************************/
-void ICACHE_FLASH_ATTR sigma_delta_setPrescaler(uint8_t prescaler)
+void ICACHE_FLASH_ATTR sigmaDeltaSetPrescaler(uint8_t prescaler)
 {
   uint32_t reg = GPSD;
 
   reg = (reg & ~(0xFF << GPSDP)) | ((prescaler & 0xFF) << GPSDP);
   GPSD = reg;
 }
+
+/******************************************************************************
+ * FunctionName : sigmaDeltaGetPrescaler
+ * Description  : get the prescaler value from the GPIO_SIGMA_DELTA register
+ * Parameters   : none
+ * Returns      : uint8 prescaler, CLK_DIV , 0-255
+*******************************************************************************/
+uint8_t ICACHE_FLASH_ATTR sigmaDeltaGetPrescaler(uint8_t prescaler)
+{
+  return (uint8_t)((GPSD >> GPSDP) & 0xFF);
+}
diff --git a/cores/esp8266/sigma_delta.h b/cores/esp8266/sigma_delta.h
index 3af2ac8080..ee7a06927b 100644
--- a/cores/esp8266/sigma_delta.h
+++ b/cores/esp8266/sigma_delta.h
@@ -31,77 +31,16 @@ THE TARGET FREQUENCY IS DEFINED AS:
 
 FREQ = 80,000,000/prescaler * target /256  HZ,     0<target<128
 FREQ = 80,000,000/prescaler * (256-target) /256  HZ,     128<target<256
-target: duty ,0-255
-prescaler: clk_div,0-255
+target: duty cycle,range 0-255
+prescaler: is a clock divider, range 0-255
 so the target and prescale will both affect the freq.
+CPU_FREQ has no influence on the sigma delta frequency.
 
 Usage :
-1. sigma_delta_enable() : activate the sigma delta source with default prescalar (0) & target (0)
-2. sigma_delta_attachPin(pin), any pin 0..15, TBC if gpio16 supports sigma-delta source
+1. sigmaDeltaSetup(0,f) : activate the sigma delta source with frequency f and default duty cycle (0)
+2. sigmaDeltaAttachPin(pin), any pin 0..15, TBC if gpio16 supports sigma-delta source
      This will set the pin to NORMAL output mode (pinMode(pin,OUTPUT))
-3. sigma_delta_setPrescaler(uint8_t) : reduce the output frequencies
-4. sigma_delta_setTarget(uint8_t) : set the output signal duty cycle, duty cycle = target/256
-
-5. sigma_delta_detachPin(pin), this will revert the pin to NORMAL output mode & GPIO source. 
-The sigma delta source remains on until :
-6. sigma_delta_disable()
-
-copy this code as example :
-
-#include "sigma_delta.h"
-
-void setup() {
-
-  Serial.begin(115200);
-  pinMode(BUILTIN_LED,OUTPUT); // blinkie & sigma-delta mix
-  
-  uint32 pin = 4; //D2
-  sigma_delta_enable();
-  //sigma_delta_disable();
-  sigma_delta_attachPin(BUILTIN_LED);
-  sigma_delta_attachPin(4); // D2
-  
-  sigma_delta_setPrescaler(255);
-
-  Serial.println();
-  Serial.println("Start Sigma Delta Example\n");
-  Serial.println("Attached gpio4 to the sigma delta source\n");
-  Serial.printf("Current target = %i, prescaler = %i\n",sigma_delta_getTarget(),sigma_delta_getPrescaler());
-}
-
-void loop() {
- 
-  uint8_t target, iRepeat;
-  
-  Serial.println("Attaching the built in led to the sigma delta source now\n");
-  Serial.printf("Current target = %i, prescaler = %i\n",sigma_delta_getTarget(),sigma_delta_getPrescaler());
-  sigma_delta_attachPin(BUILTIN_LED);
-  
-  Serial.println("dimming builtin led...\n");
-  for (iRepeat=0;iRepeat<10;iRepeat++)
-  {
-    for (target=0; target<255;target=target+5)
-    {
-      sigma_delta_setTarget(target);
-      delay(10);
-    }
-    
-    for (target=255; target>0;target=target-5)
-    {
-      sigma_delta_setTarget(target);
-      delay(10);
-    }
-    
-  }
-  Serial.println("detaching builtin led & playing a blinkie\n");
-  sigma_delta_detachPin(BUILTIN_LED);
-  for (iRepeat=0;iRepeat<20;iRepeat++)
-  {
-    digitalWrite(BUILTIN_LED,!digitalRead(BUILTIN_LED));
-    delay(500);
-  }
-    
-}
+3. sigmaDeltaWrite(0,dc) : set the output signal duty cycle, duty cycle = dc/256
 
 *******************************************************************************/
 
@@ -112,15 +51,20 @@ void loop() {
 extern "C" {
 #endif
 
-void sigma_delta_enable(void);
-void sigma_delta_disable(void);
-void sigma_delta_attachPin(uint8_t pin);
-void sigma_delta_detachPin(uint8_t pin);
-bool sigma_delta_isPinAttached(uint8_t pin);
-uint8_t sigma_delta_getTarget(void);
-void sigma_delta_setTarget(uint8_t target);
-uint8_t sigma_delta_getPrescaler(void);
-void sigma_delta_setPrescaler(uint8_t prescaler);
+//channel parameter is unused (only for ESP32 compatibility) freq 1220-312500 duty 0-255
+void        sigmaDeltaEnable(void);
+void        sigmaDeltaDisable(void);
+uint32_t    sigmaDeltaSetup(uint8_t channel, uint32_t freq);
+void        sigmaDeltaWrite(uint8_t channel, uint8_t duty);
+uint8_t     sigmaDeltaRead(uint8_t channel = 0);
+void        sigmaDeltaAttachPin(uint8_t pin, uint8_t channel = 0);
+void        sigmaDeltaDetachPin(uint8_t pin);
+bool        sigmaDeltaIsPinAttached(uint8_t pin);
+
+// alternative way to control the sigma delta generator frequency
+uint8_t     sigmaDeltaGetPrescaler(void);
+void        sigmaDeltaSetPrescaler(uint8_t prescaler);
+
 
 #ifdef __cplusplus
 }

From a1f88866371bb4134fd89e7c28f7846afda24bf5 Mon Sep 17 00:00:00 2001
From: stefaandesmet2003 <stefaandesmet2003@yahoo.co.uk>
Date: Tue, 23 Jan 2018 21:52:39 +0100
Subject: [PATCH 05/14] modified interface in line with ESP32 implementation

---
 .../SigmaDeltaDemo/SigmaDeltaDemo.ino         | 62 +++++--------------
 1 file changed, 15 insertions(+), 47 deletions(-)

diff --git a/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
index bc1390807f..3df61310c5 100644
--- a/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
+++ b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
@@ -1,84 +1,52 @@
-/*
-  Sigma Delta Generator example
-  
-  This example demonstrates the use of the ESP8266 internal hardware sigma delta source.
-  Each GPIO pin or multiple pins can be connected to the one sigma delta source.
-  THE sigma delta output frequency is defined by the ESP8266 hardware as:
+/* Any copyright is dedicated to the Public Domain. */
 
-  FREQ = 80,000,000/prescaler * target /256  HZ,          0<target<128
-  FREQ = 80,000,000/prescaler * (256-target) /256  HZ,    128<target<256
-  with :
-  target: 0-255, defines the 8-bit duty cycle of the output signal, , duty cycle = target/256
-  prescaler: 0-255, reduce the output frequencies
-  
-  so both the target and prescaler will affect the freq.
-  
-  Differences with Arduino library analogWrite :
-  - the arduino analogWrite pwm uses a hardware timer and ISR to generate the pwm signal. The sigma delta pwm doesn't need a hardware timer. 
-    The FRC1 timer can then be used for other purposes.
-  - the arduino analogWrite pwm produces a more or less fixed frequency around 900Hz. The sigma delta source produces a variable output frequency, 
-    that depends on the duty cycle. Example, with prescaler = 10, the output frequency varies between 31,kHz and 4MHz
-  - the sigma delta source produces much higher frequencies. This allows the output to be easily smoothed by a RC-filter and realise a decent 8-bit DAC
-  - the arduino analogWrite pwm has a higher resolution, default 12-bit, and up to 16-bit resolution. The sigma delta source has only 8-bit resolution
-    
-  The example doesn't require additional hardware.
-  
-  With an RC-filter (for example R=17k & C=100nF), a 'DC' output signal can be obtained with voltage between 0 and 3.3V
-  For higher value capacitors, it might be necessary to add a high-speed buffer between the esp8266 output and RC-filter to limit the current ac load on the 
-  pin output driver.
-
-*/
 #include "sigma_delta.h"
 
 void setup() {
 
   Serial.begin(115200);
   pinMode(BUILTIN_LED,OUTPUT); // blinkie & sigma-delta mix
+  uint32_t reqFreq = 1000;
+  uint32_t realFreq;
   
-  uint32 pin = 4; //D2
-  sigma_delta_enable();
-  //sigma_delta_disable();
-  sigma_delta_attachPin(BUILTIN_LED);
-  sigma_delta_attachPin(4); // D2
-  
-  sigma_delta_setPrescaler(255);
+  realFreq = sigmaDeltaSetup(0,reqFreq); // chose a low frequency
 
   Serial.println();
   Serial.println("Start Sigma Delta Example\n");
-  Serial.println("Attached gpio4 to the sigma delta source\n");
-  Serial.printf("Current target = %i, prescaler = %i\n",sigma_delta_getTarget(),sigma_delta_getPrescaler());
+  Serial.printf("Frequency = %u\n",realFreq);
+  
 }
 
 void loop() {
  
-  uint8_t target, iRepeat;
+  uint8_t duty, iRepeat;
   
   Serial.println("Attaching the built in led to the sigma delta source now\n");
-  Serial.printf("Current target = %i, prescaler = %i\n",sigma_delta_getTarget(),sigma_delta_getPrescaler());
-  sigma_delta_attachPin(BUILTIN_LED);
+  Serial.printf("Current duty = %i, prescaler = %i\n",sigmaDeltaRead(),sigmaDeltaGetPrescaler());
+  sigmaDeltaAttachPin(BUILTIN_LED);
   
   Serial.println("dimming builtin led...\n");
   for (iRepeat=0;iRepeat<10;iRepeat++)
   {
-    for (target=0; target<255;target=target+5)
+    for (duty=0; duty<255;duty=duty+5)
     {
-      sigma_delta_setTarget(target);
+      sigmaDeltaWrite(0,duty);
       delay(10);
     }
     
-    for (target=255; target>0;target=target-5)
+    for (duty=255; duty>0;duty=duty-5)
     {
-      sigma_delta_setTarget(target);
+      sigmaDeltaWrite(0,duty);
       delay(10);
     }
     
   }
   Serial.println("detaching builtin led & playing a blinkie\n");
-  sigma_delta_detachPin(BUILTIN_LED);
+  sigmaDeltaDetachPin(BUILTIN_LED);
   for (iRepeat=0;iRepeat<20;iRepeat++)
   {
     digitalWrite(BUILTIN_LED,!digitalRead(BUILTIN_LED));
     delay(500);
   }
     
-}
+}

From 385b7a2c5d16fbce8268e58f8a612b33e57f0d73 Mon Sep 17 00:00:00 2001
From: stefaandesmet2003 <stefaandesmet2003@yahoo.co.uk>
Date: Fri, 9 Mar 2018 19:35:00 +0100
Subject: [PATCH 06/14] changes requested by earlphilhower

cleanup
---
 cores/esp8266/core_esp8266_sigma_delta.c | 30 ++++++++++++++++++++----
 1 file changed, 25 insertions(+), 5 deletions(-)

diff --git a/cores/esp8266/core_esp8266_sigma_delta.c b/cores/esp8266/core_esp8266_sigma_delta.c
index 37d1fca33d..183b94e034 100644
--- a/cores/esp8266/core_esp8266_sigma_delta.c
+++ b/cores/esp8266/core_esp8266_sigma_delta.c
@@ -1,3 +1,24 @@
+/*
+  core_esp8266_sigma_delta.c - sigma delta library for esp8266
+  
+  Copyright (c) 2014 Ivan Grokhotkov. All rights reserved.
+  This file is part of the esp8266 core for Arduino environment.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
 #include "Arduino.h" // using pinMode
 
 // definitions in esp8266_peri.h style
@@ -29,7 +50,7 @@ void ICACHE_FLASH_ATTR sigmaDeltaDisable()
 }
 
 /******************************************************************************
- * FunctionName : sigma_delta_attachPin
+ * FunctionName : sigmaDeltaAttachPin
  * Description  : connects the sigma delta source to a physical output pin
  * Parameters   : pin (0..15), channel = unused, for compatibility with ESP32
  * Returns      : none
@@ -46,7 +67,7 @@ void ICACHE_FLASH_ATTR sigmaDeltaAttachPin(uint8_t pin, uint8_t channel)
 }
 
 /******************************************************************************
- * FunctionName : sigma_delta_detachPin
+ * FunctionName : sigmaDeltaDetachPin
  * Description  : disconnects the sigma delta source from a physical output pin
  * Parameters   : pin (0..16)
  * Returns      : none
@@ -93,7 +114,6 @@ uint32_t ICACHE_FLASH_ATTR sigmaDeltaSetup(uint8_t channel, uint32_t freq)
   }
   sigmaDeltaEnable();
   sigmaDeltaSetPrescaler ((uint8_t) prescaler);
-  //sigmaDeltaSetTarget ((uint8_t) 0x80); // 50% duty cycle
   
   return 10000000/((prescaler + 1) * 32);
 }
@@ -116,8 +136,8 @@ void ICACHE_FLASH_ATTR sigmaDeltaWrite(uint8_t channel, uint8_t duty)
 }
 /******************************************************************************
  * FunctionName : sigmaDeltaRead
- * Description  : set the duty cycle for the sigma-delta source
- * Parameters   : none, channel = unused, for compatibility with ESP32
+ * Description  : get the duty cycle for the sigma-delta source
+ * Parameters   : channel = unused, for compatibility with ESP32
  * Returns      : uint8_t duty cycle value 0..255
 *******************************************************************************/
 uint8_t ICACHE_FLASH_ATTR sigmaDeltaRead(uint8_t channel)

From a60f9494878b0ed5a6fb533ee09d78b085149020 Mon Sep 17 00:00:00 2001
From: stefaandesmet2003 <stefaandesmet2003@yahoo.co.uk>
Date: Fri, 9 Mar 2018 19:47:27 +0100
Subject: [PATCH 07/14] update for travis style_check

---
 .../SigmaDeltaDemo/SigmaDeltaDemo.ino         | 98 +++++++++----------
 1 file changed, 47 insertions(+), 51 deletions(-)

diff --git a/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
index 3df61310c5..45f312404b 100644
--- a/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
+++ b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
@@ -1,52 +1,48 @@
-/* Any copyright is dedicated to the Public Domain. */
-
-#include "sigma_delta.h"
-
-void setup() {
-
-  Serial.begin(115200);
-  pinMode(BUILTIN_LED,OUTPUT); // blinkie & sigma-delta mix
-  uint32_t reqFreq = 1000;
-  uint32_t realFreq;
-  
-  realFreq = sigmaDeltaSetup(0,reqFreq); // chose a low frequency
-
-  Serial.println();
-  Serial.println("Start Sigma Delta Example\n");
-  Serial.printf("Frequency = %u\n",realFreq);
-  
-}
-
-void loop() {
- 
-  uint8_t duty, iRepeat;
-  
-  Serial.println("Attaching the built in led to the sigma delta source now\n");
-  Serial.printf("Current duty = %i, prescaler = %i\n",sigmaDeltaRead(),sigmaDeltaGetPrescaler());
-  sigmaDeltaAttachPin(BUILTIN_LED);
-  
-  Serial.println("dimming builtin led...\n");
-  for (iRepeat=0;iRepeat<10;iRepeat++)
-  {
-    for (duty=0; duty<255;duty=duty+5)
-    {
-      sigmaDeltaWrite(0,duty);
-      delay(10);
-    }
-    
-    for (duty=255; duty>0;duty=duty-5)
-    {
-      sigmaDeltaWrite(0,duty);
-      delay(10);
-    }
-    
-  }
-  Serial.println("detaching builtin led & playing a blinkie\n");
-  sigmaDeltaDetachPin(BUILTIN_LED);
-  for (iRepeat=0;iRepeat<20;iRepeat++)
-  {
-    digitalWrite(BUILTIN_LED,!digitalRead(BUILTIN_LED));
-    delay(500);
-  }
-    
+/* Any copyright is dedicated to the Public Domain. */
+
+#include "sigma_delta.h"
+
+void setup() {
+
+  Serial.begin(115200);
+  pinMode(BUILTIN_LED, OUTPUT); // blinkie & sigma-delta mix
+  uint32_t reqFreq = 1000;
+  uint32_t realFreq;
+  
+  realFreq = sigmaDeltaSetup(0, reqFreq); // chose a low frequency
+
+  Serial.println();
+  Serial.println("Start Sigma Delta Example\n");
+  Serial.printf("Frequency = %u\n", realFreq);
+  
+}
+
+void loop() {
+ 
+  uint8_t duty, iRepeat;
+  
+  Serial.println("Attaching the built in led to the sigma delta source now\n");
+  Serial.printf("Current duty = %i, prescaler = %i\n", sigmaDeltaRead(), sigmaDeltaGetPrescaler());
+  sigmaDeltaAttachPin(BUILTIN_LED);
+  
+  Serial.println("dimming builtin led...\n");
+  for (iRepeat = 0; iRepeat < 10; iRepeat++) {
+    for (duty=0; duty < 255; duty = duty + 5) {
+      sigmaDeltaWrite(0, duty);
+      delay(10);
+    }
+    
+    for (duty= 255; duty > 0; duty = duty - 5) {
+      sigmaDeltaWrite(0, duty);
+      delay(10);
+    }
+    
+  }
+  Serial.println("detaching builtin led & playing a blinkie\n");
+  sigmaDeltaDetachPin(BUILTIN_LED);
+  for (iRepeat = 0; iRepeat < 20; iRepeat++) {
+    digitalWrite(BUILTIN_LED, !digitalRead(BUILTIN_LED));
+    delay(500);
+  }
+    
 }

From 717bdc3652ed3c1ccb7695f9b5f7dec13fc1d145 Mon Sep 17 00:00:00 2001
From: stefaandesmet2003 <stefaandesmet2003@yahoo.co.uk>
Date: Fri, 9 Mar 2018 20:00:40 +0100
Subject: [PATCH 08/14] remove unused parameter in sigmaDeltaGetPrescaler()

---
 cores/esp8266/core_esp8266_sigma_delta.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cores/esp8266/core_esp8266_sigma_delta.c b/cores/esp8266/core_esp8266_sigma_delta.c
index 183b94e034..1e16d041e4 100644
--- a/cores/esp8266/core_esp8266_sigma_delta.c
+++ b/cores/esp8266/core_esp8266_sigma_delta.c
@@ -166,7 +166,7 @@ void ICACHE_FLASH_ATTR sigmaDeltaSetPrescaler(uint8_t prescaler)
  * Parameters   : none
  * Returns      : uint8 prescaler, CLK_DIV , 0-255
 *******************************************************************************/
-uint8_t ICACHE_FLASH_ATTR sigmaDeltaGetPrescaler(uint8_t prescaler)
+uint8_t ICACHE_FLASH_ATTR sigmaDeltaGetPrescaler(void)
 {
   return (uint8_t)((GPSD >> GPSDP) & 0xFF);
 }

From 4c7ad74773b22d39ecba1181cff6683761dbbcef Mon Sep 17 00:00:00 2001
From: stefaandesmet2003 <stefaandesmet2003@yahoo.co.uk>
Date: Fri, 9 Mar 2018 20:26:43 +0100
Subject: [PATCH 09/14] travis doesn't like compiler warnings

---
 cores/esp8266/core_esp8266_sigma_delta.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/cores/esp8266/core_esp8266_sigma_delta.c b/cores/esp8266/core_esp8266_sigma_delta.c
index 1e16d041e4..d101401c2e 100644
--- a/cores/esp8266/core_esp8266_sigma_delta.c
+++ b/cores/esp8266/core_esp8266_sigma_delta.c
@@ -27,6 +27,8 @@
 #define GPSDP 8  // prescaler, 8 bits
 #define GPSDE 16 // enable
 
+void sigmaDeltaSetPrescaler(uint8_t prescaler); // avoids compiler warning
+
 /******************************************************************************
  * FunctionName : sigmaDeltaEnable
  * Description  : enable the internal sigma delta source

From 0a1189e2fc51882146fc1a987477057ebbf9a151 Mon Sep 17 00:00:00 2001
From: stefaandesmet2003 <stefaandesmet2003@yahoo.co.uk>
Date: Fri, 9 Mar 2018 21:29:27 +0100
Subject: [PATCH 10/14] correct comment for travis

---
 cores/esp8266/sigma_delta.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/cores/esp8266/sigma_delta.h b/cores/esp8266/sigma_delta.h
index ee7a06927b..6792f931cb 100644
--- a/cores/esp8266/sigma_delta.h
+++ b/cores/esp8266/sigma_delta.h
@@ -19,8 +19,7 @@
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  */
  
- /*
-/******************************************************************************
+ /*******************************************************************************
  * Info Sigma delta module
 
 This module controls the esp8266 internal sigma delta source

From 83aeecdcf57cc2e7a50e615159ad15dd84c5c76a Mon Sep 17 00:00:00 2001
From: stefaandesmet2003 <stefaandesmet2003@yahoo.co.uk>
Date: Fri, 9 Mar 2018 21:30:58 +0100
Subject: [PATCH 11/14] changed BUILTIN_LED to LED_BUILTIN

travis complains about BUILTIN_LED  being deprecated
---
 .../esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
index 45f312404b..b255d8ca83 100644
--- a/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
+++ b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
@@ -5,7 +5,7 @@
 void setup() {
 
   Serial.begin(115200);
-  pinMode(BUILTIN_LED, OUTPUT); // blinkie & sigma-delta mix
+  pinMode(LED_BUILTIN, OUTPUT); // blinkie & sigma-delta mix
   uint32_t reqFreq = 1000;
   uint32_t realFreq;
   
@@ -23,7 +23,7 @@ void loop() {
   
   Serial.println("Attaching the built in led to the sigma delta source now\n");
   Serial.printf("Current duty = %i, prescaler = %i\n", sigmaDeltaRead(), sigmaDeltaGetPrescaler());
-  sigmaDeltaAttachPin(BUILTIN_LED);
+  sigmaDeltaAttachPin(LED_BUILTIN);
   
   Serial.println("dimming builtin led...\n");
   for (iRepeat = 0; iRepeat < 10; iRepeat++) {
@@ -39,10 +39,12 @@ void loop() {
     
   }
   Serial.println("detaching builtin led & playing a blinkie\n");
-  sigmaDeltaDetachPin(BUILTIN_LED);
+  sigmaDeltaDetachPin(LED_BUILTIN);
   for (iRepeat = 0; iRepeat < 20; iRepeat++) {
-    digitalWrite(BUILTIN_LED, !digitalRead(BUILTIN_LED));
+    digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
     delay(500);
   }
+  
+  uint8_t prescaler = sigmaDeltaGetPrescaler();
     
 }

From 4ebb183481a434233a7038ab94be6b05f1184dd2 Mon Sep 17 00:00:00 2001
From: stefaandesmet2003 <stefaandesmet2003@yahoo.co.uk>
Date: Fri, 9 Mar 2018 22:07:12 +0100
Subject: [PATCH 12/14] remove unused test code

---
 libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
index b255d8ca83..6fe2678164 100644
--- a/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
+++ b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
@@ -43,8 +43,5 @@ void loop() {
   for (iRepeat = 0; iRepeat < 20; iRepeat++) {
     digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
     delay(500);
-  }
-  
-  uint8_t prescaler = sigmaDeltaGetPrescaler();
-    
+  } 
 }

From ab7204c77916541786812d337678a1499daf814d Mon Sep 17 00:00:00 2001
From: Stefaan De Smet <stefaandesmet2003@yahoo.co.uk>
Date: Sat, 10 Mar 2018 10:13:49 +0100
Subject: [PATCH 13/14] for travis style_check

---
 .../SigmaDeltaDemo/SigmaDeltaDemo.ino         | 94 +++++++++----------
 1 file changed, 47 insertions(+), 47 deletions(-)

diff --git a/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
index 6fe2678164..acb4410f61 100644
--- a/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
+++ b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
@@ -1,47 +1,47 @@
-/* Any copyright is dedicated to the Public Domain. */
-
-#include "sigma_delta.h"
-
-void setup() {
-
-  Serial.begin(115200);
-  pinMode(LED_BUILTIN, OUTPUT); // blinkie & sigma-delta mix
-  uint32_t reqFreq = 1000;
-  uint32_t realFreq;
-  
-  realFreq = sigmaDeltaSetup(0, reqFreq); // chose a low frequency
-
-  Serial.println();
-  Serial.println("Start Sigma Delta Example\n");
-  Serial.printf("Frequency = %u\n", realFreq);
-  
-}
-
-void loop() {
- 
-  uint8_t duty, iRepeat;
-  
-  Serial.println("Attaching the built in led to the sigma delta source now\n");
-  Serial.printf("Current duty = %i, prescaler = %i\n", sigmaDeltaRead(), sigmaDeltaGetPrescaler());
-  sigmaDeltaAttachPin(LED_BUILTIN);
-  
-  Serial.println("dimming builtin led...\n");
-  for (iRepeat = 0; iRepeat < 10; iRepeat++) {
-    for (duty=0; duty < 255; duty = duty + 5) {
-      sigmaDeltaWrite(0, duty);
-      delay(10);
-    }
-    
-    for (duty= 255; duty > 0; duty = duty - 5) {
-      sigmaDeltaWrite(0, duty);
-      delay(10);
-    }
-    
-  }
-  Serial.println("detaching builtin led & playing a blinkie\n");
-  sigmaDeltaDetachPin(LED_BUILTIN);
-  for (iRepeat = 0; iRepeat < 20; iRepeat++) {
-    digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
-    delay(500);
-  } 
-}
+/* Any copyright is dedicated to the Public Domain. */
+
+#include "sigma_delta.h"
+
+void setup() {
+
+  Serial.begin(115200);
+  pinMode(LED_BUILTIN, OUTPUT); // blinkie & sigma-delta mix
+  uint32_t reqFreq = 1000;
+  uint32_t realFreq;
+  
+  realFreq = sigmaDeltaSetup(0, reqFreq); // chose a low frequency
+
+  Serial.println();
+  Serial.println("Start Sigma Delta Example\n");
+  Serial.printf("Frequency = %u\n", realFreq);
+  
+}
+
+void loop() {
+ 
+  uint8_t duty, iRepeat;
+  
+  Serial.println("Attaching the built in led to the sigma delta source now\n");
+  Serial.printf("Current duty = %i, prescaler = %i\n", sigmaDeltaRead(), sigmaDeltaGetPrescaler());
+  sigmaDeltaAttachPin(LED_BUILTIN);
+  
+  Serial.println("dimming builtin led...\n");
+  for (iRepeat = 0; iRepeat < 10; iRepeat++) {
+    for (duty=0; duty < 255; duty = duty + 5) {
+      sigmaDeltaWrite(0, duty);
+      delay(10);
+    }
+    
+    for (duty= 255; duty > 0; duty = duty - 5) {
+      sigmaDeltaWrite(0, duty);
+      delay(10);
+    }
+    
+  }
+  Serial.println("detaching builtin led & playing a blinkie\n");
+  sigmaDeltaDetachPin(LED_BUILTIN);
+  for (iRepeat = 0; iRepeat < 20; iRepeat++) {
+    digitalWrite(LED_BUILTIN, !digitalRead(LED_BUILTIN));
+    delay(500);
+  } 
+}

From d67fa534ffe21881b3249c2b704be521b31a5de3 Mon Sep 17 00:00:00 2001
From: Stefaan De Smet <stefaandesmet2003@yahoo.co.uk>
Date: Sat, 10 Mar 2018 10:31:41 +0100
Subject: [PATCH 14/14] another attempt for travis style_check

---
 libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
index acb4410f61..e5286ccb05 100644
--- a/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
+++ b/libraries/esp8266/examples/SigmaDeltaDemo/SigmaDeltaDemo.ino
@@ -27,12 +27,12 @@ void loop() {
   
   Serial.println("dimming builtin led...\n");
   for (iRepeat = 0; iRepeat < 10; iRepeat++) {
-    for (duty=0; duty < 255; duty = duty + 5) {
+    for (duty = 0; duty < 255; duty = duty + 5) {
       sigmaDeltaWrite(0, duty);
       delay(10);
     }
     
-    for (duty= 255; duty > 0; duty = duty - 5) {
+    for (duty = 255; duty > 0; duty = duty - 5) {
       sigmaDeltaWrite(0, duty);
       delay(10);
     }