TenderLoins:
I'm trying to send POST data via a SIM900 module. The process is to create the large POST string by strcat'ing variables together, then set the SIM900 module up to send, then using hardware serial to output the char array @ 19200.
Whatever goes through serial shouldn't matter if it's all at once or in pieces, does it? The SIM900 gets serial data 1 char at a time... would a small delay between chars screw it up?
So instead of assembling a 7000 byte string and then sending it, why not just send the pieces that you would have been appending to the buffer? And for debug, use a terminal program on your PC to capture serial and maybe send up debug lines too.
Think of serial write as a kind of buffer you can feed bytes to.