From ab81e338f1d3a6c8103839c5fdfc284e62d1e7f0 Mon Sep 17 00:00:00 2001
From: Benjamin Valentin <benjamin.valentin@ml-pa.com>
Date: Wed, 18 Jan 2023 01:41:41 +0100
Subject: [PATCH] cpu/sam0_common: implement 16 bit mode by oversampling

---
 cpu/sam0_common/include/periph_cpu_common.h |  8 +++++++-
 cpu/sam0_common/periph/adc.c                | 21 ++++++++++++++-------
 2 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/cpu/sam0_common/include/periph_cpu_common.h b/cpu/sam0_common/include/periph_cpu_common.h
index 9e992b18438be..7e08b7bf756a1 100644
--- a/cpu/sam0_common/include/periph_cpu_common.h
+++ b/cpu/sam0_common/include/periph_cpu_common.h
@@ -821,11 +821,17 @@ typedef enum {
     ADC_RES_10BIT = ADC_CTRLC_RESSEL_10BIT_Val, /**< ADC resolution: 10 bit */
     ADC_RES_12BIT = ADC_CTRLC_RESSEL_12BIT_Val, /**< ADC resolution: 12 bit */
 #endif
+    ADC_RES_16BIT_2SAMPL    = ( 1 << 2) | 0x1,  /**< sum of 2 12 bit samples    */
+    ADC_RES_16BIT_4SAMPL    = ( 2 << 2) | 0x1,  /**< sum of 4 12 bit samples    */
+    ADC_RES_16BIT_8SAMPL    = ( 3 << 2) | 0x1,  /**< sum of 8 12 bit samples    */
+    ADC_RES_16BIT_16SAMPL   = ( 4 << 2) | 0x1,  /**< sum of 16 12 bit samples   */
     ADC_RES_14BIT = 0xfe,                       /**< not supported */
-    ADC_RES_16BIT = 0xfd                        /**< not supported */
 } adc_res_t;
+
+#define ADC_RES_16BIT   ADC_RES_16BIT_16SAMPL   /**< default to 16x oversampling */
 #endif /* DOXYGEN */
 
+
 /**
  * @name Ethernet peripheral parameters
  * @{
diff --git a/cpu/sam0_common/periph/adc.c b/cpu/sam0_common/periph/adc.c
index 3c906842b03c5..75c9d9da45e61 100644
--- a/cpu/sam0_common/periph/adc.c
+++ b/cpu/sam0_common/periph/adc.c
@@ -181,11 +181,7 @@ static void _setup_calibration(Adc *dev)
 
 static int _adc_configure(Adc *dev, adc_res_t res)
 {
-    /* Individual comparison necessary because ADC Resolution Bits are not
-     * numerically in order and 16Bit (averaging - not currently supported)
-     * falls between 12bit and 10bit.  See datasheet for details */
-    if (!((res == ADC_RES_8BIT) || (res == ADC_RES_10BIT) ||
-          (res == ADC_RES_12BIT))){
+    if ((res == ADC_RES_6BIT) || (res == ADC_RES_14BIT)) {
         return -1;
     }
 
@@ -203,10 +199,10 @@ static int _adc_configure(Adc *dev, adc_res_t res)
     /* Set ADC resolution */
 #ifdef ADC_CTRLC_RESSEL
     /* Reset resolution bits in CTRLC */
-    dev->CTRLC.bit.RESSEL = res;
+    dev->CTRLC.bit.RESSEL = res & 0x3;
 #else
     /* Reset resolution bits in CTRLB */
-    dev->CTRLB.bit.RESSEL = res;
+    dev->CTRLB.bit.RESSEL = res & 0x3;
 #endif
 
     /* Set Voltage Reference */
@@ -241,6 +237,12 @@ static int _adc_configure(Adc *dev, adc_res_t res)
     }
 #endif
 
+    if ((res & 0x3) == 1) {
+        dev->AVGCTRL.reg = ADC_AVGCTRL_SAMPLENUM(res >> 2);
+    } else {
+        dev->AVGCTRL.reg = 0;
+    }
+
     /*  Enable ADC Module */
     dev->CTRLA.reg |= ADC_CTRLA_ENABLE;
     _wait_syncbusy(dev);
@@ -335,5 +337,10 @@ int32_t adc_sample(adc_t line, adc_res_t res)
         result *= 2;
     }
 
+    /* 16 bit mode is implemented as oversampling */
+    if ((res & 0x3) == 1) {
+        result <<= (4 - (res >> 2));
+    }
+
     return result;
 }