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drivers: i2s: Improve precision in PLLI2S VCO calculation

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Minor rework to perform the PLLI2S VCO computations in floating point as
per the original seemingly intent.

Signed-off-by: Raul Pando <raul.pando@bytegrity.co.uk>
This commit is contained in:
Raul Pando 2023-01-15 20:04:11 +00:00 • committed by Carles Cufí
commit 0acc7fdd58
1 changed files with 5 additions and 8 deletions
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13
drivers/i2s/i2s_ll_stm32.c
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@ -130,7 +130,7 @@ static int i2s_stm32_set_clock(const struct device *dev,
{
const struct i2s_stm32_cfg *cfg = dev->config;
uint32_t pll_src = LL_RCC_PLL_GetMainSource();
int freq_in;
float freq_in;
uint8_t i2s_div, i2s_odd;
freq_in = (pll_src == LL_RCC_PLLSOURCE_HSI) ?
@ -157,12 +157,9 @@ static int i2s_stm32_set_clock(const struct device *dev,
LOG_DBG("PLLI2S is locked");
/* Adjust freq_in according to PLLM, PLLN, PLLR */
float freq_tmp;
freq_tmp = freq_in / CONFIG_I2S_STM32_PLLI2S_PLLM;
freq_tmp *= CONFIG_I2S_STM32_PLLI2S_PLLN;
freq_tmp /= CONFIG_I2S_STM32_PLLI2S_PLLR;
freq_in = (int) freq_tmp;
freq_in /= CONFIG_I2S_STM32_PLLI2S_PLLM;
freq_in *= CONFIG_I2S_STM32_PLLI2S_PLLN;
freq_in /= CONFIG_I2S_STM32_PLLI2S_PLLR;
#endif /* CONFIG_I2S_STM32_USE_PLLI2S_ENABLE */
/* Select clock source */
@ -174,7 +171,7 @@ static int i2s_stm32_set_clock(const struct device *dev,
* following formula:
* (i2s_div * 2) + i2s_odd
*/
i2s_div = div_round_closest(freq_in, bit_clk_freq);
i2s_div = div_round_closest((uint32_t) freq_in, bit_clk_freq);
i2s_odd = (i2s_div & 0x1) ? 1 : 0;
i2s_div >>= 1;