MOD54417 \TA pin usefulness as GPIO

[addonray]

Hi,

Can GPIO pin PA4 in the MOD54417 actually be used? I had it set as a GPIO input with a low state at power up. It somehow interferes (acting as \TA?) with the program loading from flash (a debug build). MTTY output shows a message indicating a bad load. If I remove the PA4 pin from the peripheral holding it low, my application starts normally. We are using the FlexBus in 8 bit mode, using CS5, if that makes any difference.

Thanks,

Ray

[mbrown]

Based on how the MOD5441x boots, you can't be holding it low when the application starts. The bus is initially configured to read a parallel flash which runs on the same FlexBus exposed externally. When you hold the \TA pin low at boot, you're forcing the FlexBus to terminate reads from the parallel flash before the data is appropriately ready and the processor decides the application is corrupted. At this point, the alternate monitor is loaded from a serial flash. This is what's giving you the memory corruption message.

You should be able to use it as GPIO after the application has booted, however I haven't had time to test whether you can still perform flash reads and writes while the TA pin is used as GPIO. The chip should be set to automatically acknowledge read/write commands and largely ignore the TA pin, but this doesn't appear to be the case (at least) for boot.

[addonray]

Thank you - that's about what I suspected was going on. It seemed to raise Cain with the debugger, too. I'll just avoid using that GPIO pin.