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>

docs/stm32f1.md

@@ -22,7 +22,8 @@ Fixed pins
 
 The UART used for communication with the host is fixed to pins PA9 (TX) and PA10
 (RX). SWD pins (PA13/PA14) are enabled for debugging and cannot be used for any
-I/O.
+I/O. SPI uses pins PB13/PB14/PB15, but the pins can be used as general I/O if
+SPI is not used.
 
 Digital I/O
 ===========
@@ -44,4 +45,5 @@ PC0-PC5).
 SPI
 ===
 
-SPI support is currently unimplemented.
+SPI uses pin PB13 (SCK), PB14 (MISO) and PB15 (MOSI). The clock speed range is
+0.15..18 MHz. Chip select pins do not have any restrictions.

src/stm32f1/Kconfig

@@ -7,6 +7,7 @@ config STM32F1_SELECT
     default y
     select HAVE_GPIO
     select HAVE_GPIO_ADC
+    select HAVE_GPIO_SPI
     select HAVE_USER_INTERFACE
 
 config BOARD_DIRECTORY

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);
+}

src/stm32f1/gpio.h

@@ -30,4 +30,11 @@ uint32_t gpio_adc_sample(struct gpio_adc g);
 uint16_t gpio_adc_read(struct gpio_adc g);
 void gpio_adc_cancel_sample(struct gpio_adc g);
 
+struct spi_config {
+    SPI_TypeDef config;
+};
+struct spi_config spi_setup(uint32_t bus, uint8_t mode, uint32_t rate);
+void spi_transfer(struct spi_config config, uint8_t receive_data,
+                  uint8_t len, uint8_t *data);
+
 #endif // gpio.h

src/stm32f1/main.c

@@ -14,6 +14,7 @@
 #include "stm32f1xx_ll_iwdg.h"
 #include "stm32f1xx_ll_gpio.h"
 #include "stm32f1xx_ll_adc.h"
+#include "stm32f1xx_ll_spi.h"
 #include "sched.h" // sched_main
 
 DECL_CONSTANT(MCU, "stm32f103");
@@ -108,6 +109,13 @@ void adc_config(void)
     LL_ADC_REG_SetSequencerLength(ADC1, LL_ADC_REG_SEQ_SCAN_DISABLE);
 }
 
+void spi_config(void)
+{
+    LL_APB1_GRP1_EnableClock(LL_APB1_GRP1_PERIPH_SPI2);
+    LL_SPI_SetNSSMode(SPI2, LL_SPI_NSS_SOFT);
+    LL_SPI_SetMode(SPI2, LL_SPI_MODE_MASTER);
+}
+
 void io_config(void)
 {
     LL_APB2_GRP1_EnableClock(LL_APB2_GRP1_PERIPH_AFIO);
@@ -131,6 +139,7 @@ main(void)
     clock_config();
     adc_config();
     io_config();
+    spi_config();
     sched_main();
     return 0;
 }