Added code to 'get' the gpio mode of a pin, and have used it in SPIClass::begin() to store and reinstate the pin mode of the SPI NSS pin. This is a work around for 'features' in the STM32 silicon, which seem to change the GPIO mode of the SPI NSS (hardware - 'Software Select' pin)

Author: rogerclarkmelbourne

STM32F1/cores/maple/libmaple/gpio_f1.c

@@ -138,6 +138,23 @@ void gpio_set_mode(gpio_dev *dev, uint8 pin, gpio_pin_mode mode) {
     }
 }
 
+gpio_pin_mode gpio_get_mode(gpio_dev *dev, uint8 pin) {
+    gpio_reg_map *regs = dev->regs;
+    __io uint32 *cr = &regs->CRL + (pin >> 3);
+    uint32 shift = (pin & 0x7) * 4;
+    uint32 tmp = *cr;
+
+	uint32 crMode = (*cr>>shift) & 0x0F;
+	
+	// could be pull up or pull down. Nee to check the ODR
+	if (crMode==GPIO_INPUT_PD && ((regs->ODR >> pin) & 0x01) !=0 )
+	{
+		crMode = GPIO_INPUT_PU;
+	}
+	
+    return(crMode);
+}
+
 /*
  * AFIO
  */

STM32F1/libraries/SPI/src/SPI.cpp

@@ -119,17 +119,43 @@ SPIClass::SPIClass(uint32 spi_num) {
  */
 
 void SPIClass::begin(void) {
+	gpio_pin_mode nssPinMode;
+	int nssPin;
     if (dataMode >= 4) {
         ASSERT(0);
         return;
     }
+	
+#if BOARD_NR_SPI >= 1
+	if (this->spi_d == SPI1)
+	{
+		nssPin=BOARD_SPI1_NSS_PIN;
+	}
+#endif
+#if BOARD_NR_SPI >= 2
+	if (this->spi_d == SPI2)
+	{
+		nssPin=BOARD_SPI2_NSS_PIN;
+	}
+#endif
+#if BOARD_NR_SPI >= 3
+	if (this->spi_d == SPI3)
+	{
+		nssPin=BOARD_SPI3_NSS_PIN;
+	}
+#endif	
+
+
+	nssPinMode = gpio_get_mode(PIN_MAP[nssPin].gpio_device, PIN_MAP[nssPin].gpio_bit);// get and save NSS pin mode
+	
     uint32 flags = ((bitOrder == MSBFIRST ? SPI_FRAME_MSB : SPI_FRAME_LSB) | SPI_DFF_8_BIT | SPI_SW_SLAVE | SPI_SOFT_SS);
     spi_init(spi_d);
     configure_gpios(spi_d, 1);
 	#ifdef SPI_DEBUG
 	Serial.print("spi_master_enable("); Serial.print(clockDivider); Serial.print(","); Serial.print(dataMode); Serial.print(","); Serial.print(flags); Serial.println(")");
 	#endif
     spi_master_enable(spi_d, (spi_baud_rate)clockDivider, (spi_mode)dataMode, flags);
+	gpio_set_mode(PIN_MAP[nssPin].gpio_device, PIN_MAP[nssPin].gpio_bit, nssPinMode);// restore pin mode of nss pin (work around for bug in the STM32)
 }
 
 void SPIClass::beginSlave(void) {

STM32F1/system/libmaple/include/libmaple/gpio.h

@@ -71,7 +71,7 @@ void gpio_init(gpio_dev *dev);
 void gpio_init_all(void);
 /* TODO flags argument version? */
 void gpio_set_mode(gpio_dev *dev, uint8 pin, gpio_pin_mode mode);
-
+gpio_pin_mode gpio_get_mode(gpio_dev *dev, uint8 pin);
 /**
  * @brief Get a GPIO port's corresponding EXTI port configuration.
  * @param dev GPIO port whose exti_cfg to return.