SPI data registers

Makefile

@@ -35,9 +35,9 @@ boot.bin: boot.elf
 	@echo "OBJCOPY $@"
 	@$(OBJCOPY) -O binary boot.elf boot.bin
 
-boot.elf: $(objs) src/spi.o
+boot.elf: $(objs) src/lcd_spi.o
 	@echo "LD      $@"
-	@$(LD) -T boot/stm32f429.ld $(objs) src/spi.o -o $@
+	@$(LD) -T boot/stm32f429.ld $(objs) src/lcd_spi.o -o $@
 
 %.o: %.c
 	@echo "CC      $@"

arch/stm32f429/registers/spi.c

@@ -9,6 +9,7 @@
 
 #define SPI_CR1_OFFSET 0x00
 #define SPI_SR_OFFSET  0x08
+#define SPI_DR_OFFSET  0x0C
 
 char * SPI_REGISTER_ADDRESS(SPI_t spi, int registerOffset) {
   char * spiBaseAddress[6] = {
@@ -25,3 +26,7 @@ SPI_CR1_t * SPI_CR1(SPI_t spi) {
 SPI_SR_t * SPI_SR(SPI_t spi) {
   return (SPI_SR_t *)SPI_REGISTER_ADDRESS(spi, SPI_SR_OFFSET);
 }
+
+SPI_DR_t * SPI_DR(SPI_t spi) {
+  return (SPI_DR_t *)SPI_REGISTER_ADDRESS(spi, SPI_DR_OFFSET);
+}

arch/stm32f429/registers/spi.h

@@ -1,3 +1,5 @@
+#include <stdint.h>
+
 typedef enum {
   SPI1 = 0,
   SPI2 = 1,
@@ -25,7 +27,6 @@ typedef enum {
   SPI_DFF_16_BITS = 1
 } SPI_DFF_t;
 
-
 typedef struct {
   unsigned int CPHA:1;
   unsigned int CPOL:1;
@@ -61,3 +62,8 @@ typedef struct {
 } SPI_SR_t;
 
 SPI_SR_t * SPI_SR(SPI_t spi);
+
+#pragma mark - SPI data registers
+
+typedef uint16_t SPI_DR_t;
+SPI_DR_t * SPI_DR(SPI_t spi);

src/lcd_spi.c

@@ -0,0 +1,101 @@
+#include <registers.h>
+#include <FreeRTOS.h>
+#include <task.h>
+#include <timers.h>
+#include <semphr.h>
+
+/* This code sends data to the onboard LCD over SPI
+ *
+ * The LCD has two interfaces, SPI and direct RGB.
+ * We'll only use SPI in this one.
+ *
+ * The documentation gives the following mapping
+ * Pin name  -  LCD-SPI
+ * NRST  -  Reset
+ * PC2   - CSX // Chip select for LCD
+ * PD13 - DCX // Data/Command register
+ * PF7 - SCL // SPI Clock
+ * PF9 - SDI/SDO // MOSI
+ *
+ * See UM1670 p. 19 to 24. */
+
+/* We'll need to figure out which GPIO pins this maps to, and in which
+ * Alternate Function mode. STM32F429 datasheet p78-79 says:
+ * PF6 in AF5 = SPI5_NSS
+ * PF7 in AF5 = SPI5_SCK
+ * PF8 in AF5 = SPI5_MISO
+ * PF9 in AF5 = SPI5_MOSI
+ */
+
+/* In case we want to monitor this, here's a color-mapping
+ *
+ * PF6 - SPI5_NSS - Yellow
+ * PF7 - SPI5_SCK - Green
+ * PF8 - SPI5_MISO - Red
+ * PF9 - SPI5_MOSI - Blue
+ */
+
+void SpiSend(void * pvParameters) {
+  uint16_t value = 0;
+  while(1) {
+    SPI_SR_t * spi_status = SPI_SR(SPI5);
+    SPI_DR_t * spi_data_register = SPI_DR(SPI5);
+    if (spi_status->BSY == 0) {
+      *spi_data_register = value++;
+    }
+    vTaskDelay(100/portTICK_PERIOD_MS);
+  }
+}
+
+int main(int argc, char * argv[]) {
+  // We'll use GPIO pins F6-F9 to emit SPI data
+  // GPIO are grouped by letter. All GPIO groups live on the "AHB1" bus.
+  // (this is documented in the STM32F4 reference mnual, page 65)
+
+  // Step 1 : Enable clock in RCC_AHBxENR
+  RCC_AHB1ENR->GPIOFEN = 1;
+
+  // Step 2 : Configure the GPIO pin to "Alternate function number 5"
+  // This means "SPI5 on pins F6-F9", cf STM32F249 p78
+  GPIO_MODER(GPIOF)->MODER6 = GPIO_MODE_ALTERNATE_FUNCTION;
+  GPIO_MODER(GPIOF)->MODER7 = GPIO_MODE_ALTERNATE_FUNCTION;
+  GPIO_MODER(GPIOF)->MODER8 = GPIO_MODE_ALTERNATE_FUNCTION;
+  GPIO_MODER(GPIOF)->MODER9 = GPIO_MODE_ALTERNATE_FUNCTION;
+
+  // We're interested in pins 11-14, which are in the 8-16 range, so we
+  // have to deal with the "high" version of the AF register
+  GPIO_AFRL(GPIOF)->AFRL6 = GPIO_AF_AF5;
+  GPIO_AFRL(GPIOF)->AFRL7 = GPIO_AF_AF5;
+  GPIO_AFRH(GPIOF)->AFRH8 = GPIO_AF_AF5;
+  GPIO_AFRH(GPIOF)->AFRH9 = GPIO_AF_AF5;
+
+  // Enable the SPI5 clock
+  RCC_APB2ENR->SPI5EN = 1;
+
+  // Configure the SPI port
+  // Using a C99 compound litteral. C99 guarantees all non-set values are zero
+  *SPI_CR1(SPI5) = (SPI_CR1_t){
+    .BIDIMODE = 1,
+    .BIDIOE = 1,
+    .MSTR = 1,
+    .DFF = SPI_DFF_16_BITS,
+    .CPOL = 0,
+    .BR = SPI_BR_DIV_256,
+    .SSM = 1,
+    .SSI = 1,
+    .SPE = 1
+  };
+
+  BaseType_t success = xTaskCreate(SpiSend,
+      "SpiSnd",
+      100, // Stack size
+      NULL, // Parameters
+      2,
+      NULL);
+
+  vTaskStartScheduler();
+
+  while (1) {
+    // We should never get here
+  }
+}

src/spi.c

@@ -51,43 +51,18 @@ int main(int argc, char * argv[]) {
   RCC_APB2ENR->SPI4EN = 1;
 
   // Configure the SPI port
-  /*
-    SPI_InitStruct.SPI_Direction = SPI_Direction_2Lines_FullDuplex;
-    SPI_InitStruct.SPI_Mode = SPI_Mode_Master;
-    SPI_InitStruct.SPI_DataSize = SPI_DataSize_8b;
-    SPI_InitStruct.SPI_CPOL = SPI_CPOL_Low;
-    SPI_InitStruct.SPI_CPHA = SPI_CPHA_1Edge;
-    SPI_InitStruct.SPI_NSS = SPI_NSS_Soft | SPI_NSSInternalSoft_Set;
-    SPI_InitStruct.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_256;
-    SPI_InitStruct.SPI_FirstBit = SPI_FirstBit_MSB;
-    */
-  SPI_CR1_t * SPI4_CR1 = SPI_CR1(SPI4);
-  /*
-  SPI4_CR1->BIDIMODE = 0;
-  SPI4_CR1->BIDIOE = 1;
-  SPI4_CR1->MSTR = 1;
-  SPI4_CR1->DFF = SPI_DFF_8_BITS;
-  SPI4_CR1->CPOL = 0;
-  SPI4_CR1->BR = SPI_BR_DIV_256;
-  SPI4_CR1->SSM = 1;
-  SPI4_CR1->SSI = 1;
-  SPI4_CR1->SPE = 1;
-  */
-
-  /*
-   11 0 0 1
-   0 1 1 0 1 111
-   100 */
-
-  /*
-   * 1100
-   * 1011
-   * 0111
-   * 1100
-   */
-  *(uint16_t *)SPI4_CR1 = 0xCB7C;
-
-  SPI_CR1_t output = *SPI4_CR1;
+  // Using a C99 compound litteral
+  *SPI_CR1(SPI4) = (SPI_CR1_t){
+    .BIDIMODE = 1,
+    .BIDIOE = 1,
+    .MSTR = 1,
+    .DFF = SPI_DFF_16_BITS,
+    .CPOL = 0,
+    .BR = SPI_BR_DIV_256,
+    .SSM = 1,
+    .SSI = 1,
+    .SPE = 1
+  };
 
   BaseType_t success = xTaskCreate(SpiSend,
       "SpiSnd",