First interrupt after attachInterrupt

[fulda1]

Hi,

I'm using interrupt on change in my project. Unfortunately, pin is in use before interrupt is attached. That mean, first ISR call is instantly after attachInterrupt command. As per datasheet, interrupt flag is in EXTI->INTFR. That can be cleared by write 1. I do not know, how can I clear it proper way. I'm running on CH32V203K8. Did try code like this:

EXTI->INTFR = 0xFFFF;
attachInterrupt(LN_Rx_PIN, GPIO_Mode_IN_FLOATING, LN_Rx_Start, EXTI_Mode_Interrupt, EXTI_Trigger_Falling);

but no effect.

[maxint-rd]

Hello @fulda1 -

Hmmm... I'm not sure if I can really help. What do you mean by "already used"?

I've tried to find some general clues, so for what it's worth:
To clear an interrupt flag one usually only writes the specific bit in the specific register. Most core functions use some wrapper function. For EXTI, the attachInterrupt() function in WInterrupts.cpp adds a callback function to a list somewhere within ch32_interrupt_enable(). The actual interrupt handler does the callback and clears the pending bit. For V00x and VM00X the handler is only EXTI7_0_IRQHandler(). For V203 there are many more (see interrupt.cpp).

You can use EXTI_GetITStatus(pin) to check the pin flag using binary representation of the pin. To clear the pending bit the EXTI_ClearITPendingBit() wrapper is called, with as parameter either a binary representation of the pin, or a 32-bit line value (eg. EXTI_Line0). In both cases that function simply does this:
EXTI->INTFR = EXTI_Line;
So it just set bits in the EXTernal Interrupt Flag Register. Since this seems similar to what you already do, you may need to look further at what's going on. Maybe the debugger can be helpful here?

Would it help to first call detachInterrupt()? That function calls ch32_interrupt_disable() which calls NVIC_DisableIRQ() to disable the interrupt. NVIC_DisableIRQ() and NVIC_DisableIRQ() are bothe implemented in core_riscv.h and respectively touch IRER and IENR. The V203 core_riscv.h also has the inline function NVIC_ClearPendingIRQ(IRQn_Type IRQn), which sets some IPRR register, but I don't see that function being called anywhere. Maybe it can be called for EXTI too?
(Note: The term NVIC here is is the ARM Cortex name for the interrupt controller, WCH used PFIC for RiscV).

BTW. Thank you for sending me that Flash example code. It may come in handy some time.
To share code example I sometimes create a Github Gist. These can be made public or "secret". The difference is probably if they are listed or not. After making the gist you can share the link by mentioning it, for instance in an issue, like this unrelated example.

[fulda1]

Hi,

to explain my setup. I have special needs for "software serial". It mean - wait for change interrupt on change (begin of start bit), then enable timer with baudrate for read bits (and disable interrupt on change). When byte is received, I stop timer interrupt and enable interrupt on change.
My input pin is PA3. I did few experiments with INTFR like this:

  EXTI_ClearITPendingBit((1 << 3));             // remove flag for RA3 interrupt - not works as expected
  attachInterrupt(PA3, GPIO_Mode_IN_FLOATING, LN_Rx_Start, EXTI_Mode_Interrupt, EXTI_Trigger_Falling);

but did not find working version yet.

For sure I have workaround - in ISR function LN_Rx_Start I start with condition: if (digitalRead(LN_Rx_PIN) == LOW) {...} to filter out incorrect calls.