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Merge pull request #13537 from jue89/feature/sam0-spi-frequency

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cpu/sam0_common: mitigate rounding errors of SPI baud rate calculation
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benpicco 2020-03-04 16:50:46 +01:00 committed by GitHub
commit 681678e3f3
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2 changed files with 6 additions and 3 deletions
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2
boards/samr30-xpro/include/board.h
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@ -36,7 +36,7 @@ extern "C" {
#define AT86RF2XX_PARAM_INT GPIO_PIN(PB, 0)
#define AT86RF2XX_PARAM_SLEEP GPIO_PIN(PA, 20)
#define AT86RF2XX_PARAM_RESET GPIO_PIN(PB, 15)
#define AT86RF2XX_PARAM_SPI_CLK SPI_CLK_1MHZ
#define AT86RF2XX_PARAM_SPI_CLK SPI_CLK_5MHZ
/** @}*/
/**

7
cpu/sam0_common/periph/spi.c
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@ -103,8 +103,11 @@ int spi_acquire(spi_t bus, spi_cs_t cs, spi_mode_t mode, spi_clk_t clk)
/* configure bus clock, in synchronous mode its calculated from
* BAUD.reg = (f_ref / (2 * f_bus) - 1)
* with f_ref := CLOCK_CORECLOCK as defined by the board */
const uint8_t baud = (sam0_gclk_freq(spi_config[bus].gclk_src) / (2 * clk) - 1);
* with f_ref := CLOCK_CORECLOCK as defined by the board
* to mitigate the rounding error due to integer arithmetic, the
* equation is modified to
* BAUD.reg = ((f_ref + f_bus) / (2 * f_bus) - 1) */
const uint8_t baud = ((sam0_gclk_freq(spi_config[bus].gclk_src) + clk) / (2 * clk) - 1);
/* configure device to be master and set mode and pads,
*