stm32/mphalport.c: Set AFR first before changing GPIO mode. #8539
Conversation
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I can see how this is necessary when switching a GPIO to AF, that you need to select the function first. But what about switching from AF (to eg output)? In that case wouldn't you want to leave the function as-is until after the mode is changed? Otherwise it may glitch, eg become an MCO1 pin (which is AF=0) for a brief moment before becoming an output pin. |
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How about this: if (mode == MP_HAL_PIN_MODE_ALT) {
gpio->AFR[pin >> 3] = ...;
}
gpio->MODER = ...;If switching from IN/OUT -> AF, a valid AF will be set in AFR before changing the mode, and if switching from AF -> IN/OUT, then a valid AF will be in AFR when mode is changed. |
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Yes that looks good! Would be good to also add a comment to that block to explain the subtleties. |
Done. Side note, why does this code right shifts by 2 when all the HAL libs right shift by 4? gpio->OTYPER = (gpio->OTYPER & ~(1 << pin)) | ((mode >> 2) << pin);
//H7
temp |= (((GPIO_Init->Mode & GPIO_OUTPUT_TYPE) >> 4U) << position); |
Because OTYPER is just one bit, whether it's push-pull or open-drain. In the HAL constants that bit is encoded in the second nibble, whereas in MicroPython's constants (eg MP_HAL_PIN_MODE_OPEN_DRAIN) it's encoded in the 3rd bit. |
* To avoid any I/O glitches in mp_hal_pin_config, make sure a valid alternate function is set in AFR first before switching the pin mode. When switching from AF to INPUT or OUTPUT, the AF in AFR will remain valid up until the pin mode is switched.
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Merged in 71afed1 |
AFRbefore switching GPIOMODERto GPIO_MODE_AF. This matches the GPIO configuration order in all HAL_GPIO_Init functions.Note the actual issue that I'm trying to fix: I call
mp_hal_pin_configon reset from early_init, to switch USB pins to GPIOs temporarily and then switch them back to alternate functions, and without this fix I get the following errors in dmesg: