feat(spi): allow to skip receive during transfer

Linked to stm32duino#912.

Signed-off-by: Frederic Pillon <frederic.pillon@st.com>

libraries/SPI/README.md

@@ -35,6 +35,10 @@ void setup() {
 }
 ```
 
+### Extended API
+
+* All `transfer()` API's have a new bool argument `skipReceive`. It allows to skip receive data after transmitting. Value can be `SPI_TRANSMITRECEIVE` or `SPI_TRANSMITONLY`. Default `SPI_TRANSMITRECEIVE`.
+
 #### Change default `SPI` instance pins
 It is also possible to change the default pins used by the `SPI` instance using above API:
 

libraries/SPI/src/SPI.cpp

@@ -156,21 +156,27 @@ void SPIClass::setClockDivider(uint8_t divider)
   * @brief  Transfer one byte on the SPI bus.
   *         begin() or beginTransaction() must be called at least once before.
   * @param  data: byte to send.
+  * @param  skipReceive: skip receiving data after transmit or not.
+  *         SPI_TRANSMITRECEIVE or SPI_TRANSMITONLY.
+  *         Optional, default: SPI_TRANSMITRECEIVE.
   * @return byte received from the slave.
   */
-uint8_t SPIClass::transfer(uint8_t data)
+uint8_t SPIClass::transfer(uint8_t data, bool skipReceive)
 {
-  spi_transfer(&_spi, &data, sizeof(uint8_t), SPI_TRANSFER_TIMEOUT, false);
+  spi_transfer(&_spi, &data, sizeof(uint8_t), SPI_TRANSFER_TIMEOUT, skipReceive);
   return data;
 }
 
 /**
   * @brief  Transfer two bytes on the SPI bus in 16 bits format.
   *         begin() or beginTransaction() must be called at least once before.
   * @param  data: bytes to send.
+  * @param  skipReceive: skip receiving data after transmit or not.
+  *         SPI_TRANSMITRECEIVE or SPI_TRANSMITONLY.
+  *         Optional, default: SPI_TRANSMITRECEIVE.
   * @return bytes received from the slave in 16 bits format.
   */
-uint16_t SPIClass::transfer16(uint16_t data)
+uint16_t SPIClass::transfer16(uint16_t data, bool skipReceive)
 {
   uint16_t tmp;
 
@@ -179,7 +185,7 @@ uint16_t SPIClass::transfer16(uint16_t data)
     data = tmp;
   }
   spi_transfer(&_spi, (uint8_t *)&data, sizeof(uint16_t),
-               SPI_TRANSFER_TIMEOUT, false);
+               SPI_TRANSFER_TIMEOUT, skipReceive);
 
   if (_spiSettings.bitOrder) {
     tmp = ((data & 0xff00) >> 8) | ((data & 0xff) << 8);
@@ -195,12 +201,15 @@ uint16_t SPIClass::transfer16(uint16_t data)
   * @param  buf: pointer to the bytes to send. The bytes received are copy in
   *         this buffer.
   * @param  count: number of bytes to send/receive.
+  * @param  skipReceive: skip receiving data after transmit or not.
+  *         SPI_TRANSMITRECEIVE or SPI_TRANSMITONLY.
+  *         Optional, default: SPI_TRANSMITRECEIVE.
   */
-void SPIClass::transfer(void *buf, size_t count)
+void SPIClass::transfer(void *buf, size_t count, bool skipReceive)
 {
   if ((count != 0) && (buf != NULL)) {
     spi_transfer(&_spi, ((uint8_t *)buf), count,
-                 SPI_TRANSFER_TIMEOUT, false);
+                 SPI_TRANSFER_TIMEOUT, skipReceive);
   }
 }
 

libraries/SPI/src/SPI.h

@@ -38,6 +38,9 @@ extern "C" {
 #define SPI_CLOCK_DIV64  64
 #define SPI_CLOCK_DIV128 128
 
+#define SPI_TRANSMITRECEIVE false
+#define SPI_TRANSMITONLY true
+
 // Defines a default timeout delay in milliseconds for the SPI transfer
 #ifndef SPI_TRANSFER_TIMEOUT
   #define SPI_TRANSFER_TIMEOUT 1000
@@ -131,9 +134,9 @@ class SPIClass {
     /* Transfer functions: must be called after initialization of the SPI
      * instance with begin() or beginTransaction().
      */
-    virtual uint8_t transfer(uint8_t data);
-    virtual uint16_t transfer16(uint16_t data);
-    virtual void transfer(void *buf, size_t count);
+    virtual uint8_t transfer(uint8_t data, bool skipReceive = SPI_TRANSMITRECEIVE);
+    virtual uint16_t transfer16(uint16_t data, bool skipReceive = SPI_TRANSMITRECEIVE);
+    virtual void transfer(void *buf, size_t count, bool skipReceive = SPI_TRANSMITRECEIVE);
 
     /* These methods are deprecated and kept for compatibility.
      * Use SPISettings with SPI.beginTransaction() to configure SPI parameters.