cc2538: spi: Add enable and disable functions

This makes it possible to reduce the power consumption when the SPI is unused.

Signed-off-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>

cpu/cc2538/dev/spi.c

@@ -74,8 +74,7 @@
 void
 spi_init(void)
 {
-  /* Enable the SSI peripheral */
-  REG(SYS_CTRL_RCGCSSI) |= 1;
+  spi_enable();
 
   /* Start by disabling the peripheral before configuring it */
   REG(SSI0_BASE + SSI_CR1) = 0;
@@ -110,4 +109,18 @@ spi_init(void)
   /* Enable the SSI */
   REG(SSI0_BASE + SSI_CR1) |= SSI_CR1_SSE;
 }
+/*---------------------------------------------------------------------------*/
+void
+spi_enable(void)
+{
+  /* Enable the clock for the SSI peripheral */
+  REG(SYS_CTRL_RCGCSSI) |= 1;
+}
+/*---------------------------------------------------------------------------*/
+void
+spi_disable(void)
+{
+  /* Gate the clock for the SSI peripheral */
+  REG(SYS_CTRL_RCGCSSI) &= ~1;
+}
 /** @} */

cpu/cc2538/spi-arch.h

@@ -57,6 +57,21 @@
 #define SPI_WAITFOREORx() do { \
   while(!(REG(SSI0_BASE + SSI_SR) & SSI_SR_RNE)); \
 } while (0)
+/*---------------------------------------------------------------------------*/
+/** \name Arch-specific SPI functions
+ * @{
+ */
+
+/** \brief Enables the SPI peripheral
+ */
+void spi_enable(void);
+
+/** \brief Disables the SPI peripheral
+ * \note Call this function to save power when the SPI is unused.
+ */
+void spi_disable(void);
+
+/** @} */
 
 #endif /* SPI_ARCH_H_ */