SPI: add parameter to spiclass::on transmit/on receive

[mean00]

This PR adds a parameter/cookie to the spi class onTransmit/onReceive callbacks This is useful to go back to the client class when the callback is invoked By default the parameter is null, so it should be compatible with the current API

It is especially useful when using a small RTOS like FreeRTOS

To give an example, a transfer to the screen is armed and the task waits on a semaphore The callback cookie is actually the client instance, and upon dereferencing, the semaphore is unlocked

i.e. static void Screen::screencallback(void a) { myScreen s=(Screen *)a; s->transferDone();}

[stevstrong]

I'm afraid the compatibility is not kept because you changed the first parameter (the callback function type) from void(*callback)(void) to void(*callback)(void *).

[mean00]

Indeed

[stevstrong]

I will not merge this if it does not keep backward compatibility.

[mean00]

yes, that goes without saying Even if , as it is, the api is a bit awkward and probably not used much

[stevstrong]

Closed due to missing backward compatibility. You may reopen this PR if you re-write it to be compatible.