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drivers: usb_dc_stm32: Add support for MSI clock

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When MSI clock is available and in PLL-Mode (high accuracy), use it as
USB source clock. This allows to enable USB on STM34l475 disco iot
board without having to add external oscillator.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
This commit is contained in:
Loic Poulain 2018-07-11 11:56:42 +02:00 • committed by Anas Nashif
commit a32a39f3d2
1 changed files with 18 additions and 1 deletions
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19
drivers/usb/device/usb_dc_stm32.c
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@ -223,7 +223,7 @@ static int usb_dc_stm32_clock_enable(void)
/*
* Some SoCs in STM32F0/L0/L4 series disable USB clock by
* default. We force USB clock source to PLL clock for this
* default. We force USB clock source to MSI or PLL clock for this
* SoCs. However, if these parts have an HSI48 clock, use
* that instead. Example reference manual RM0360 for
* STM32F030x4/x6/x8/xC and STM32F070x6/xB.
@ -253,11 +253,28 @@ static int usb_dc_stm32_clock_enable(void)
LL_RCC_SetUSBClockSource(LL_RCC_USB_CLKSOURCE_HSI48);
#elif defined(LL_RCC_USB_CLKSOURCE_NONE)
/* When MSI is configured in PLL mode with a 32.768 kHz clock source,
* the MSI frequency can be automatically trimmed by hardware to reach
* better than ±0.25% accuracy. In this mode the MSI can feed the USB
* device. For now, we only use MSI for USB if not already used as
* system clock source.
*/
#if defined(CONFIG_CLOCK_STM32_MSI_PLL_MODE) && !defined(CONFIG_CLOCK_STM32_SYSCLK_SRC_MSI)
LL_RCC_MSI_Enable();
while (!LL_RCC_MSI_IsReady()) {
/* Wait for MSI to become ready */
}
/* Force 48 MHz mode */
LL_RCC_MSI_EnableRangeSelection();
LL_RCC_MSI_SetRange(LL_RCC_MSIRANGE_11);
LL_RCC_SetUSBClockSource(LL_RCC_USB_CLKSOURCE_MSI);
#else
if (LL_RCC_PLL_IsReady()) {
LL_RCC_SetUSBClockSource(LL_RCC_USB_CLKSOURCE_PLL);
} else {
LOG_ERR("Unable to set USB clock source to PLL.");
}
#endif /* CONFIG_CLOCK_STM32_MSI_PLL_MODE && !CONFIG_CLOCK_STM32_SYSCLK_SRC_MSI */
#endif /* RCC_HSI48_SUPPORT / LL_RCC_USB_CLKSOURCE_NONE */
if (clock_control_on(clk, (clock_control_subsys_t *)&pclken) != 0) {