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Merge pull request #18223 from benpicco/cpu/sam0_common-spi_clk

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cpu/sam0_common: spi: limit clock to source clock
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Kevin "Tristate Tom" Weiss 2022-08-30 19:30:49 +02:00 committed by GitHub
commit 8a340fec11
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1 changed files with 7 additions and 1 deletions
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8
cpu/sam0_common/periph/spi.c
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@ -269,13 +269,19 @@ static void _init_spi(spi_t bus, SercomSpi *dev)
static void _spi_acquire(spi_t bus, spi_mode_t mode, spi_clk_t clk)
{
/* clock can't be higher than source clock */
uint32_t gclk_src = sam0_gclk_freq(spi_config[bus].gclk_src);
if (clk > gclk_src) {
clk = gclk_src;
}
/* 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
* 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);
const uint8_t baud = (gclk_src + clk) / (2 * clk) - 1;
/* configure device to be master and set mode and pads,
*