diff --git a/hardware/esp8266com/esp8266/cores/esp8266/HardwareSerial.cpp b/hardware/esp8266com/esp8266/cores/esp8266/HardwareSerial.cpp
index 87fd6dfbbe..bdcd457169 100644
--- a/hardware/esp8266com/esp8266/cores/esp8266/HardwareSerial.cpp
+++ b/hardware/esp8266com/esp8266/cores/esp8266/HardwareSerial.cpp
@@ -392,30 +392,34 @@ void uart_ignore_char(char c) {
 
 void uart0_write_char(char c) {
     if(&Serial != NULL && Serial.isTxEnabled()) {
-        if(c == '\n') {
-            Serial.write('\r');
-        }
-        Serial.write(c);
-    } else {
-        if(c == '\n') {
-            USF(0) = '\r';
+        if(Serial.availableForWrite() > 0) {
+            if(c == '\n') {
+                Serial.write('\r');
+            }
+            Serial.write(c);
+            return;
         }
-        USF(0) = c;
     }
+    if(c == '\n') {
+        USF(0) = '\r';
+    }
+    USF(0) = c;
 }
 
 void uart1_write_char(char c) {
     if(&Serial1 != NULL && Serial1.isTxEnabled()) {
-        if(c == '\n') {
-            Serial1.write('\r');
-        }
-        Serial1.write(c);
-    } else {
-        if(c == '\n') {
-            USF(1) = '\r';
+        if(Serial1.availableForWrite() > 0) {
+            if(c == '\n') {
+                Serial1.write('\r');
+            }
+            Serial1.write(c);
+            return;
         }
-        USF(1) = c;
     }
+    if(c == '\n') {
+        USF(1) = '\r';
+    }
+    USF(1) = c;
 }
 
 static int s_uart_debug_nr = UART0;
diff --git a/hardware/esp8266com/esp8266/libraries/SPI/SPI.cpp b/hardware/esp8266com/esp8266/libraries/SPI/SPI.cpp
index c96c4fcb82..7d52528ef1 100644
--- a/hardware/esp8266com/esp8266/libraries/SPI/SPI.cpp
+++ b/hardware/esp8266com/esp8266/libraries/SPI/SPI.cpp
@@ -121,14 +121,14 @@ void SPIClass::setBitOrder(uint8_t bitOrder) {
  * @return
  */
 static uint32_t ClkRegToFreq(spiClk_t * reg) {
-    return (F_CPU / ((reg->regPre + 1) * (reg->regN + 1)));
+    return (SPI_MAX_SPEED / ((reg->regPre + 1) * (reg->regN + 1)));
 }
 
 void SPIClass::setFrequency(uint32_t freq) {
     static uint32_t lastSetFrequency = 0;
     static uint32_t lastSetRegister = 0;
 
-    if(freq >= F_CPU) {
+    if(freq >= SPI_MAX_SPEED) {
         setClockDivider(0x80000000);
         return;
     }
@@ -164,7 +164,7 @@ void SPIClass::setFrequency(uint32_t freq) {
         reg.regN = calN;
 
         while(calPreVari++ <= 1) { // test different variants for Pre (we calculate in int so we miss the decimals, testing is the easyest and fastest way)
-            calPre = (((F_CPU / (reg.regN + 1)) / freq) - 1) + calPreVari;
+            calPre = (((SPI_MAX_SPEED / (reg.regN + 1)) / freq) - 1) + calPreVari;
             if(calPre > 0x1FFF) {
                 reg.regPre = 0x1FFF; // 8191
             } else if(calPre <= 0) {
diff --git a/hardware/esp8266com/esp8266/libraries/SPI/SPI.h b/hardware/esp8266com/esp8266/libraries/SPI/SPI.h
index e67b5b0d58..68d2a3dc6c 100644
--- a/hardware/esp8266com/esp8266/libraries/SPI/SPI.h
+++ b/hardware/esp8266com/esp8266/libraries/SPI/SPI.h
@@ -45,6 +45,8 @@
 #define SPI_CLOCK_DIV64 	0x04fc1001 //250 KHz
 #endif
 
+#define SPI_MAX_SPEED      (80000000L)
+
 const uint8_t SPI_MODE0 = 0x00; ///<  CPOL: 0  CPHA: 0
 const uint8_t SPI_MODE1 = 0x01; ///<  CPOL: 0  CPHA: 1
 const uint8_t SPI_MODE2 = 0x10; ///<  CPOL: 1  CPHA: 0