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Merge pull request #20084 from maribu/stm32_spi
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cpu/stm32/periph_spi: Fix /CS handling
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@maribu
maribu authored Nov 24, 2023
2 parents 8d8bd82 + f4729c2 commit 6ae0b4d
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Showing 2 changed files with 67 additions and 47 deletions.
30 changes: 30 additions & 0 deletions cpu/stm32/include/periph_cpu.h
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Original file line number Diff line number Diff line change
Expand Up @@ -170,6 +170,36 @@ typedef struct {
#define USBDEV_NUM_ENDPOINTS 8
#endif

/* unify names across STM32 families */
#ifdef SPI_CR1_CPHA_Msk
# define STM32_SPI_CPHA_Msk SPI_CR1_CPHA_Msk
#endif
#ifdef SPI_CFG2_CPHA_Msk
# define STM32_SPI_CPHA_Msk SPI_CFG2_CPHA_Msk
#endif
#ifdef SPI_CR1_CPOL_Msk
# define STM32_SPI_CPOL_Msk SPI_CR1_CPOL_Msk
#endif
#ifdef SPI_CFG2_CPOL_Msk
# define STM32_SPI_CPOL_Msk SPI_CFG2_CPOL_Msk
#endif

/**
* @name Override the SPI mode values
*
* As the mode is set in bit 3 and 2 of the configuration register, we put the
* correct configuration there
* @{
*/
#define HAVE_SPI_MODE_T
typedef enum {
SPI_MODE_0 = 0, /**< CPOL=0, CPHA=0 */
SPI_MODE_1 = STM32_SPI_CPHA_Msk, /**< CPOL=0, CPHA=1 */
SPI_MODE_2 = STM32_SPI_CPOL_Msk, /**< CPOL=1, CPHA=0 */
SPI_MODE_3 = STM32_SPI_CPOL_Msk | STM32_SPI_CPHA_Msk, /**< CPOL=1, CPHA=0 */
} spi_mode_t;
/** @} */

#endif /* !DOXYGEN */

#ifdef __cplusplus
Expand Down
84 changes: 37 additions & 47 deletions cpu/stm32/periph/spi.c
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Original file line number Diff line number Diff line change
Expand Up @@ -28,8 +28,6 @@

#include <assert.h>

#include "bitarithm.h"
#include "cpu.h"
#include "mutex.h"
#include "periph/gpio.h"
#include "periph/spi.h"
Expand Down Expand Up @@ -65,9 +63,9 @@ static mutex_t locks[SPI_NUMOF];
static uint32_t clocks[SPI_NUMOF];

/**
* @brief Clock divider cache
* @brief Clock prescaler cache
*/
static uint8_t dividers[SPI_NUMOF];
static uint8_t prescalers[SPI_NUMOF];

static inline SPI_TypeDef *dev(spi_t bus)
{
Expand All @@ -81,33 +79,24 @@ static inline bool _use_dma(const spi_conf_t *conf)
}
#endif

/**
* @brief Multiplier for clock divider calculations
*
* Makes the divider calculation fixed point
*/
#define SPI_APB_CLOCK_SHIFT (4U)
#define SPI_APB_CLOCK_MULT (1U << SPI_APB_CLOCK_SHIFT)

static uint8_t _get_clkdiv(const spi_conf_t *conf, uint32_t clock)
static uint8_t _get_prescaler(const spi_conf_t *conf, uint32_t clock)
{
uint32_t bus_clock = periph_apb_clk(conf->apbbus);
/* Shift bus_clock with SPI_APB_CLOCK_SHIFT to create a fixed point int */
uint32_t div = (bus_clock << SPI_APB_CLOCK_SHIFT) / (2 * clock);
DEBUG("[spi] clock: divider: %"PRIu32"\n", div);
/* Test if the divider is 2 or smaller, keeping the fixed point in mind */
if (div <= SPI_APB_CLOCK_MULT) {
return 0;
}
/* determine MSB and compensate back for the fixed point int shift */
uint8_t rounded_div = bitarithm_msb(div) - SPI_APB_CLOCK_SHIFT;
/* Determine if rounded_div is not a power of 2 */
if ((div & (div - 1)) != 0) {
/* increment by 1 to ensure that the clock speed at most the
* requested clock speed */
rounded_div++;
}
return rounded_div > BR_MAX ? BR_MAX : rounded_div;

uint8_t prescaler = 0;
uint32_t prescaled_clock = bus_clock >> 1;
const uint8_t prescaler_max = SPI_CR1_BR_Msk >> SPI_CR1_BR_Pos;
for (; (prescaled_clock > clock) && (prescaler < prescaler_max); prescaler++) {
prescaled_clock >>= 1;
}

/* If the callers asks for an SPI frequency of at most x, bad things will
* happen if this cannot be met. So let's have a blown assertion
* rather than runtime failures that require a logic analyzer to
* debug. */
assert(prescaled_clock <= clock);

return prescaler;
}

void spi_init(spi_t bus)
Expand Down Expand Up @@ -235,30 +224,30 @@ void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
periph_clk_en(spi_config[bus].apbbus, spi_config[bus].rccmask);
/* enable device */
if (clk != clocks[bus]) {
dividers[bus] = _get_clkdiv(&spi_config[bus], clk);
prescalers[bus] = _get_prescaler(&spi_config[bus], clk);
clocks[bus] = clk;
}
uint8_t br = dividers[bus];
uint8_t br = prescalers[bus];

DEBUG("[spi] acquire: requested clock: %"PRIu32", resulting clock: %"PRIu32
" BR divider: %u\n",
DEBUG("[spi] acquire: requested clock: %" PRIu32
" Hz, resulting clock: %" PRIu32 " Hz, BR prescaler: %u\n",
clk,
periph_apb_clk(spi_config[bus].apbbus)/(1 << (br + 1)),
br);
periph_apb_clk(spi_config[bus].apbbus) >> (br + 1),
(unsigned)br);

uint16_t cr1_settings = ((br << BR_SHIFT) | mode | SPI_CR1_MSTR);
uint16_t cr1 = ((br << BR_SHIFT) | mode | SPI_CR1_MSTR | SPI_CR1_SPE);
/* Settings to add to CR2 in addition to SPI_CR2_SETTINGS */
uint16_t cr2_extra_settings = 0;
uint16_t cr2 = SPI_CR2_SETTINGS;
if (cs != SPI_HWCS_MASK) {
cr1_settings |= (SPI_CR1_SSM | SPI_CR1_SSI);
cr1 |= (SPI_CR1_SSM | SPI_CR1_SSI);
}
else {
cr2_extra_settings = (SPI_CR2_SSOE);
cr2 = (SPI_CR2_SSOE);
}

#ifdef MODULE_PERIPH_DMA
if (_use_dma(&spi_config[bus])) {
cr2_extra_settings |= SPI_CR2_TXDMAEN | SPI_CR2_RXDMAEN;
cr2 |= SPI_CR2_TXDMAEN | SPI_CR2_RXDMAEN;

dma_acquire(spi_config[bus].tx_dma);
dma_setup(spi_config[bus].tx_dma,
Expand All @@ -277,11 +266,8 @@ void spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
0);
}
#endif
dev(bus)->CR1 = cr1_settings;
/* Only modify CR2 if needed */
if (cr2_extra_settings) {
dev(bus)->CR2 = (SPI_CR2_SETTINGS | cr2_extra_settings);
}
dev(bus)->CR1 = cr1;
dev(bus)->CR2 = cr2;
}

void spi_release(spi_t bus)
Expand Down Expand Up @@ -396,10 +382,12 @@ void spi_transfer_bytes(spi_t bus, spi_cs_t cs, bool cont,
assert(out || in);

/* active the given chip select line */
dev(bus)->CR1 |= (SPI_CR1_SPE); /* this pulls the HW CS line low */
if ((cs != SPI_HWCS_MASK) && gpio_is_valid(cs)) {
gpio_clear((gpio_t)cs);
}
else {
dev(bus)->CR2 |= SPI_CR2_SSOE;
}

#ifdef MODULE_PERIPH_DMA
if (_use_dma(&spi_config[bus])) {
Expand All @@ -414,9 +402,11 @@ void spi_transfer_bytes(spi_t bus, spi_cs_t cs, bool cont,

/* release the chip select if not specified differently */
if ((!cont) && gpio_is_valid(cs)) {
dev(bus)->CR1 &= ~(SPI_CR1_SPE); /* pull HW CS line high */
if (cs != SPI_HWCS_MASK) {
gpio_set((gpio_t)cs);
}
else {
dev(bus)->CR2 &= ~(SPI_CR2_SSOE);
}
}
}

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