Bootloader kicking out modded firmware
Guys, I wonder if there is more to the checksum scheme than we first thought. I made what should have been a minor mod (a JSR to an existing function) using some unused data bytes. The mod works if I execute (not upload) the firmware - giving me a sequence of beeps everytime a filename is loaded into memory. (very interesting effect, really). When I upload and replace the existing firmware, the bootloader kicks me out. I did let pv2tool update the checksum. Am I, or are we, missing something?

Not really - I'm pretty sure the onboard memory in the ASIC is only 4kB - and the lower 1kB is common to all (library, init, etc). It takes quite a bit of code just to setup the camera and the banking structures. So, they chose to "bank" the upper 3kB of the internal SRAM. I suppose it was cheaper than making the internal SRAM larger.

Just curious, really - since I haven't been able to make my cable as yet. But ... has anyone made a rough memory map of the 6550? I keep finding myself having difficulty visualizing what's where and how it works. (Mind you, I once was a hotshot assembly programmer, and worked on devices that relied heavily on overlays and bankswitching, so am not unfamiliar with the concepts ...)

Yep, either check out John Maushammers site, or mine (I compiled all the info and made it look pretty) http://www.maushammer.com/systems/dakotadigital/lcd.html http://home.comcast.net/~jshamlet/intro.html

Add it to the list of stuff I need to do. Go to the URL, convert all the letters to uppercase, and try it again... ;)