OK, I'm back. After a timeout caused by my buying and subsequent (ab)using of a Yamaha MOX6 (Yes!!!) I returned to my midibox project. As noted above and implemented in the meantime, all text output (as for now) goes to the text area of the T6963C. I can see all the MIOS messages now, while also being able to do graphics, including text-as-graphics. Think of it like a PC: first booting in text mode and then switching to graphics mode. Just for the looks, I seriously consider dumping screens full of fake driver initialization messages on the display while booting, like on a unix system.
Anyway, the next item on my list before starting the project for real is driving an SD card. I bought one of these cheapo SD card holders for $2 on ebay, the sort that don't work because there's a missing ground connection on them. So I fixed that, and while being at it also breadboarded a level shifter using diodes and a transistor. That's the short version of where I'm now. Don't ask for the long one.
The basics seem to work: I can write bits to the card using the MSSP module (SPI) of the 18F4620, and get as far as the card responding to the GO_IDLE_STATE request (CMD0). Then I get illegal command responses for everything else. I understand that "older" cards are quite sensitive to the initial bit rate not being to high, so I'd like to use the TMR2/2 option using Timer2, but get an infinite boot-reset loop.
Timer2 is not used in MIOS, is it? What are the minimum steps to setup the timer2 to, say 500kHz, no interrupt. Yes, I do read the data sheet, but that also lied about the SPI setup.
Thanks for suggestions (also tricks/need-to-knows about SD card communication)