Hi Alex,
ive got a spca536 based player too but i cannot flash the player with the ISP-Tool thats on the CD so mine is still working ;-). Anyway, since im more intersted in reversing it then watching movies on this small 2.5" display i disassembled one of the rom files which is supposed to contain the isp-/boot-loader. i found sth. that looks like UART init code at least it uses a value of 115200 (most probably this refers to the speed of 115200 baud) and it seems like the software expects the cpu to run at a speed of 48MHz. Furthermore i found a few potential intersting memory addresses:
0xAC700000 - r3000 memory address where this code is mapped to
0xD0004010 - start of DRAM (either that or this its a pointer)
0xB0000010/21/22/23 - location of UART registers ???
you mentioned a russian page dedicated to reversing spca536, do you have a link or sth (I dont understand russian though). Ive put the disassembly and the rom file here:
http://mitglied.lycos.de/luluba/spca536/
btw, since you mentioned that you were able to flash your player, i found a dll called usb_cam.dll/lib (which is used by CutImage soft) which offers promising interface routines towards developing a flash utility for downloading the firmware like for example:
ISP_Dnload(char *,ulong,ulong,ulong,int,void (*)(char *))
- have a look at the exports of the dll.
regards