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GPIO4 bootload handshake / strange behevior

Hello everyone,

I am working on bootloading the DSP via a host processor and the mcBsp0 module.

So far I have configured the SSI on the host side (the timing diagrams look fine) but I have some strange result when I try to upload the code to the 5502 DSP.

The bootmode is Standard Serial Boot Mode, I doubled check all the connections.

In the bootloader documentation they state that after every single word the DSP will drive GPIO4 high whilst it is busy and then put it back to low state.

In my case, GPIO4 is driven high at a very strange moment as it corresponds to the 4th bit of the 3rd word being sent... Then is will handshake regularly with the same interval.

I did a screenshot of the scope:

The top signal is GPIO, followed by the data line, chip select and clock of the mcBsp.

I programmed everything via CCS and my host model is ARM-M3.