PWM_FullConfiguration.ino with open drain output?

[ericwoud]

I want to start on a new project. I would like to use the hardware timer to send a signal, so I think PWM_FullConfiguration.ino will be a good starting point.

However I would like it to be an open drain output.

The example states: No need to configure pin, it will be done by HardwareTimer configuration

So will it work if I would add this to the code?

 gpio_set_mode(digitalPinToPort(pin), PIN_MAP[pin].gpio_bit, GPIO_OUTPUT_OD); // set open drain output

If so, where to add it?

[fpistm]

Hi @ericwoud
it seems you used this core: https://github.com/rogerclarkmelbourne/Arduino_STM32
https://github.com/rogerclarkmelbourne/Arduino_STM32/blob/341cd894516f747f14108de5da593dad99900ae0/STM32F1/cores/maple/libmaple/gpio_f1.c#L124

Not the one linked to STM32Examples:
https://github.com/stm32duino/Arduino_Core_STM32
which do not have gpio_set_mode

So you should ask on the forum in the dedicated libmaple core section:
https://www.stm32duino.com/viewforum.php?f=63

[ABOSTM]

Yes, overwriting the weak PinMap_TIM sounds good to me for both Open drain and PullUp.
By the way, I am curious to know why you need Open Drain configuration ?

[ericwoud]

I was thinking of transforming one existing HDMI-CEC library to use a hardware timer and interrupts.

Because I want to minimize the hardware, I am going to use a stm32(f4), because it has open drain outputs, where many other boards do not. I can connect the CEC pin directly to a pin, switching it between input without pullup and open collector output.

I have ordered 2 stm32f401's so I hope I can start soon.

[ericwoud]

I have ordered the STM32F401CCU6, meaning I would need:
https://github.com/stm32duino/Arduino_Core_STM32/blob/main/variants/STM32F4xx/F401CC(F-U-Y)_F401C(B-D-E)(U-Y)/PeripheralPins.c

Let's say I want pin PA_2 on timer 5, I see:

 {PA_2_ALT1, TIM5,  STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM5, 3, 0)}, // TIM5_CH3

I would need to change it to:

 {PA_2_ALT1, TIM5,  STM_PIN_DATA_EXT(STM_MODE_AF_OD, GPIO_NOPULL, GPIO_AF2_TIM5, 3, 0)}, // TIM5_CH3

Should this be good enough to make sure I never activate the input pullup, or even worse, force the output to high voltage?

[ABOSTM]

Yes that sound good.

Did you know that some STM32 MCU support Hardware HDMI-CEC ?
Even within F4 series, like STM32F446RET
https://www.st.com/en/microcontrollers-microprocessors/stm32f446.html
(but not supported on stm32f401)

[ericwoud]

I know, also some STM32F0xx, but it is not as cheap and available as the STM32F401.