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STM32F417: DCMI HSYNC signal / dead pin (?)

Question asked by winkler.tom on Nov 20, 2012

I've spent several days working on getting the DCMI interface on my custom STM32F147 board working. I'm able to configure my camera sensor (OV7725) via I2C and I'm also getting the VSYNC signals from the sensor (the ISR corresponding to the DCMI_IT_VSYNC interrupt is properly triggered). However, I'm unable to get any HSYNC signals from the sensor. With a scope attached to the sensor I verified that proper HSYNC signals are generated by the sensor. But the STM32F4 doesn't seem to receive them. The ISR that corresponds to the DCMI_IT_LINE (which represents the HSYNC if I understood the reference correctly) interrupt gets never called. I check my code multiple times and I'm pretty sure that the interrupt handling code is correct.

I'm using the PA4 pin on my STM32F4 (I'm using a package with 144 pins - so PA4 is the only choice for HSYNC in my case). I did some additional tests with this pin and made some interesting findings. First, I can toggle PA4 without problems. However, if I want to use it as an external interrupt source (EXTI) it this does not work. I cross-checked my EXTI code using various other pins and with those it was working flawlessly.

My conclusion so far is that PA4 might got damaged (not sure how...). I now wanted to ask the experts how likely it is that a pin can be toggled but using it as an input does not work. What could be the reasons for such a damage? Is there some way to validate (self check...) the correct functionality of a pin?

I'm open for all your suggestions and ideas!

Thank you