STM32 SPI: nbits should be unsigned. Valid range is 4-16 for F3 and L4. 8 or 16 for others.

ChangeLog

@@ -12393,7 +12393,6 @@
 	  (2016-07-23).
 	* Freedom-K64F:  Add PWM support.  From Jordan MacIntyre (2016-07-25).
 
-
 7.18 2016-xx-xx Gregory Nutt <gnutt@nuttx.org>
 
 	* drivers/serial/pty.c, serial.c, usbdev/cdcacm.c, include/nuttx/fs/ioctl.h:
@@ -12564,7 +12563,8 @@
 	  (2016-08-12).
 	* arch/sim/src: Add a simulated oneshot lowerhalf driver (2016-08-12).
 	* arch/arm/src/stm32: STM32F3 SPI:  Fix the number of bit setting for
-	  the F3.  It works differently than for other STM32 parts (2016-08-12).
+	  the F3.  That and data packing work differently on the STM32F3 than
+	  for other STM32 parts (2016-08-12).
 	* arch/arm/stm32 and stm32l4: Enabling SPI DMA loses other bits in CR2
 	  (2016-08-13).
 	* arch/arm/src/stm32: STM32F3 SPI:  Cannot write always 16-bit value to

arch/arm/src/stm32/stm32_spi.c

@@ -182,7 +182,7 @@ struct stm32_spidev_s
   sem_t            exclsem;    /* Held while chip is selected for mutual exclusion */
   uint32_t         frequency;  /* Requested clock frequency */
   uint32_t         actual;     /* Actual clock frequency */
-  int8_t           nbits;      /* Width of word in bits (8 or 16) */
+  uint8_t          nbits;      /* Width of word in bits (4 through 16) */
   uint8_t          mode;       /* Mode 0,1,2,3 */
 };
 

arch/arm/src/stm32l4/stm32l4_spi.c

@@ -163,7 +163,7 @@ struct stm32l4_spidev_s
   sem_t            exclsem;    /* Held while chip is selected for mutual exclusion */
   uint32_t         frequency;  /* Requested clock frequency */
   uint32_t         actual;     /* Actual clock frequency */
-  int8_t           nbits;      /* Width of word in bits (8 or 16) */
+  uint8_t          nbits;      /* Width of word in bits (4 through 16) */
   uint8_t          mode;       /* Mode 0,1,2,3 */
 };