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spi: Add delay before disabling SPI to avoid truncated clock/data signals #1506

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Merged
merged 1 commit into from
Sep 24, 2021
Merged

spi: Add delay before disabling SPI to avoid truncated clock/data signals #1506

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33 changes: 33 additions & 0 deletions libraries/SPI/src/utility/spi_com.c
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,7 @@
*
******************************************************************************
*/
#include "wiring_time.h"
#include "core_debug.h"
#include "stm32_def.h"
#include "utility/spi_com.h"
Expand Down Expand Up @@ -183,6 +184,28 @@ uint32_t spi_getClkFreq(spi_t *obj)
return spi_freq;
}


#if defined(STM32H7xx) || defined(STM32MP1xx)
/**
* @brief Compute delay before disabling SPI
* See https://github.com/stm32duino/Arduino_Core_STM32/issues/1294
* Computed delay is half SPI clock
* @param obj : pointer to spi_t structure
* @retval Disable delay in microsecondes
*/
static uint32_t compute_disable_delay(spi_t *obj)
{
uint32_t spi_freq = spi_getClkFreqInst(obj->spi);
uint32_t disable_delay;
uint32_t prescaler;
SPI_HandleTypeDef *handle = &(obj->handle);

prescaler = 1 << ((handle->Init.BaudRatePrescaler >> SPI_CFG1_MBR_Pos) + 1);
disable_delay = ((prescaler * 1000000) / spi_freq) / 2;
return disable_delay;
}
#endif

/**
* @brief SPI initialization function
* @param obj : pointer to spi_t structure
Expand Down Expand Up @@ -258,6 +281,11 @@ void spi_init(spi_t *obj, uint32_t speed, spi_mode_e mode, uint8_t msb)
handle->Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_256;
}

#if defined(STM32H7xx) || defined(STM32MP1xx)
// Compute disable delay as baudrate has been modified
obj->disable_delay = compute_disable_delay(obj);
#endif

handle->Init.Direction = SPI_DIRECTION_2LINES;

if ((mode == SPI_MODE_0) || (mode == SPI_MODE_2)) {
Expand Down Expand Up @@ -490,6 +518,11 @@ spi_status_e spi_transfer(spi_t *obj, uint8_t *tx_buffer, uint8_t *rx_buffer,
}

#if defined(STM32H7xx) || defined(STM32MP1xx)
// Add a delay before disabling SPI otherwise last-bit/last-clock may be truncated
// See https://github.com/stm32duino/Arduino_Core_STM32/issues/1294
// Computed delay is half SPI clock
delayMicroseconds(obj->disable_delay);

/* Close transfer */
/* Clear flags */
LL_SPI_ClearFlag_EOT(_SPI);
Expand Down
5 changes: 5 additions & 0 deletions libraries/SPI/src/utility/spi_com.h
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,11 @@ struct spi_s {
PinName pin_mosi;
PinName pin_sclk;
PinName pin_ssel;
#if defined(STM32H7xx) || defined(STM32MP1xx)
// Delay before disabling SPI.
// See https://github.com/stm32duino/Arduino_Core_STM32/issues/1294
uint32_t disable_delay;
#endif
};

typedef struct spi_s spi_t;
Expand Down