stm32f1: add SPI support

Add basic SPI support and associated documentation.

v2: remove baud rate check, fix baud rate calculations
v3: finish transaction with BSY check, disable SPI when not in use

Signed-off-by: Grigori Goronzy <greg@chown.ath.cx>

1 files changed, 101 insertions, 0 deletions

diff --git a/src/stm32f1/gpio.c b/src/stm32f1/gpio.c
index caadf277..ed507496 100644
--- a/src/stm32f1/gpio.c
+++ b/src/stm32f1/gpio.c
@@ -11,8 +11,10 @@
 #include "compiler.h" // ARRAY_SIZE
 #include "gpio.h" // gpio_out_setup
 #include "stm32f1xx.h"
+#include "stm32f1xx_ll_rcc.h"
 #include "stm32f1xx_ll_gpio.h"
 #include "stm32f1xx_ll_adc.h"
+#include "stm32f1xx_ll_spi.h"
 #include "sched.h" // sched_shutdown
 #include "board/irq.h"
 #include "board/io.h"
@@ -219,3 +221,102 @@ gpio_adc_cancel_sample(struct gpio_adc g)
         LL_ADC_ClearFlag_EOS(ADC1);
     }
 }
+
+/****************************************************************
+ * Serial Peripheral Interface (SPI) pins
+ ****************************************************************/
+
+void spi_set_mode(SPI_TypeDef *spi, uint8_t mode)
+{
+    switch (mode) {
+    case 0:
+        LL_SPI_SetClockPolarity(spi, LL_SPI_POLARITY_LOW);
+        LL_SPI_SetClockPhase(spi, LL_SPI_PHASE_1EDGE);
+        break;
+    case 1:
+        LL_SPI_SetClockPolarity(spi, LL_SPI_POLARITY_LOW);
+        LL_SPI_SetClockPhase(spi, LL_SPI_PHASE_2EDGE);
+        break;
+    case 2:
+        LL_SPI_SetClockPolarity(spi, LL_SPI_POLARITY_HIGH);
+        LL_SPI_SetClockPhase(spi, LL_SPI_PHASE_1EDGE);
+        break;
+    case 3:
+        LL_SPI_SetClockPolarity(spi, LL_SPI_POLARITY_HIGH);
+        LL_SPI_SetClockPhase(spi, LL_SPI_PHASE_2EDGE);
+        break;
+    default:
+        shutdown("Invalid SPI mode");
+    }
+}
+
+void spi_set_baudrate(SPI_TypeDef *spi, uint32_t rate)
+{
+    const uint32_t pclk = __LL_RCC_CALC_PCLK1_FREQ(SystemCoreClock, LL_RCC_GetAPB1Prescaler());
+    const uint32_t prescaler = pclk / rate;
+
+    uint32_t setting = LL_SPI_BAUDRATEPRESCALER_DIV256;
+    if (prescaler <= 2)
+        setting = LL_SPI_BAUDRATEPRESCALER_DIV2;
+    else if (prescaler <= 4)
+        setting = LL_SPI_BAUDRATEPRESCALER_DIV4;
+    else if (prescaler <= 8)
+        setting = LL_SPI_BAUDRATEPRESCALER_DIV8;
+    else if (prescaler <= 16)
+        setting = LL_SPI_BAUDRATEPRESCALER_DIV16;
+    else if (prescaler <= 32)
+        setting = LL_SPI_BAUDRATEPRESCALER_DIV32;
+    else if (prescaler <= 64)
+        setting = LL_SPI_BAUDRATEPRESCALER_DIV64;
+    else if (prescaler <= 128)
+        setting = LL_SPI_BAUDRATEPRESCALER_DIV128;
+
+    LL_SPI_SetBaudRatePrescaler(spi, setting);
+}
+
+void spi_init_pins(void)
+{
+    LL_GPIO_SetPinMode(GPIOB, LL_GPIO_PIN_13, LL_GPIO_MODE_ALTERNATE);
+    LL_GPIO_SetPinMode(GPIOB, LL_GPIO_PIN_14, LL_GPIO_MODE_INPUT);
+    LL_GPIO_SetPinMode(GPIOB, LL_GPIO_PIN_15, LL_GPIO_MODE_ALTERNATE);
+    LL_GPIO_SetPinOutputType(GPIOB, LL_GPIO_PIN_13, LL_GPIO_OUTPUT_PUSHPULL);
+    LL_GPIO_SetPinPull(GPIOB, LL_GPIO_PIN_14, LL_GPIO_PULL_UP);
+    LL_GPIO_SetPinOutputType(GPIOB, LL_GPIO_PIN_15, LL_GPIO_OUTPUT_PUSHPULL);
+}
+
+struct spi_config
+spi_setup(uint32_t bus, uint8_t mode, uint32_t rate)
+{
+    struct spi_config config;
+    config.config = *SPI2;
+
+    if (bus > 0 || !rate)
+        shutdown("Invalid spi_setup parameters");
+
+    spi_init_pins();
+    spi_set_mode(&config.config, mode);
+    spi_set_baudrate(&config.config, rate);
+
+    return config;
+}
+
+void
+spi_transfer(struct spi_config config, uint8_t receive_data,
+             uint8_t len, uint8_t *data)
+{
+    *SPI2 = config.config;
+    LL_SPI_Enable(SPI2);
+
+    while (len--) {
+        LL_SPI_TransmitData8(SPI2, *data);
+        while (!LL_SPI_IsActiveFlag_TXE(SPI2));
+        if (receive_data) {
+            while (!LL_SPI_IsActiveFlag_RXNE(SPI2));
+            *data = LL_SPI_ReceiveData8(SPI2);
+        }
+        data++;
+    }
+
+    while (LL_SPI_IsActiveFlag_BSY(SPI2));
+    LL_SPI_Disable(SPI2);
+}