Strange errors if "Hard limits" are enabled

[lakeroe]

I've always had strange errors in bCNC when zeroing X, Y or Z axis or pressing the stop button several times in a row. The errors only happen if "Hard limits" are enabled ($21=1). After some debugging I found that EXTI15_10_IRQHandler() in limits.c gets triggered although it should not. I think the problem is somehow related to USB connected to pins PA11/PA12 and the Y/Z limit switches connected to PB11/PB12. After changing the Y/Z limit switches to PA1/9 the problem is gone.

So maybe that's worth some more debugging ...

[lakeroe]

After some more testing I found that PA9 also interferes with something and can not be used as input. PA10 works fine though ...
So in summary: If using USB and "Hard limits" PA9, PA11 and PA12 can not be used

[lakeroe]

I think I've now found the root cause of the problem.
In limits.c the function GPIO_EXTILineConfig (in stm32f10x_gpio.c) is called which does a read/modify/write of the "External interrupt configuration registers (AFIO_EXTICRx)" to select the appropriate interrupt input pin.
This function is implemented in a wrong way what causes the wrong input be selected (for a very short time) everytime it's called and triggers an false interrupt.
After changing

tmp = ((uint32_t)0x0F) << (0x04 * (GPIO_PinSource & (uint8_t)0x03));
AFIO->EXTICR[GPIO_PinSource >> 0x02] &= ~tmp;
AFIO->EXTICR[GPIO_PinSource >> 0x02] |= (((uint32_t)GPIO_PortSource) << (0x04 * (GPIO_PinSource & (uint8_t)0x03)));

to

tmp = AFIO->EXTICR[GPIO_PinSource >> 0x02];
tmp &= ~(((uint32_t)0x0F) << (0x04 * (GPIO_PinSource & (uint8_t)0x03)));
tmp |= (((uint32_t)GPIO_PortSource) << (0x04 * (GPIO_PinSource & (uint8_t)0x03)));
AFIO->EXTICR[GPIO_PinSource >> 0x02] = tmp;

the hard limit interrupts (on pins PB10/11/12) work as expected and no more false interrupts are triggered (when pressing the stop-button in bCNC).

Best regards,
lakeroe