A chap who has one of my EEPROM boards reported that the machine (model B) would not boot if DFS 2.26 was programmed into the EEPROM. In fact it would only boot with the 16kB EPROM he has.
I got a Model B (not B+) recently from ebay with the 1770 fitted (fixed it) and had a go myself.
- It will boot and work with a 16kB EPROM.
- It will boot then crash on enter with a 64kB EPROM (not EE) programmed BASIC,DFS,EXMON2,ADT. (I tried without ADT too)
- It will short beep then hang with flashing cursor and no banner if DFS is in EEPROM.
My conclusion is that DFS 2.26 detects B/B+ at some point and uses shadow RAM and/or different OS entry points. Does anyone know how DFS detects the B+? I would like to know why the EPROM & EE have different (crashing) behaviour.
Does anyone have a commented dissasembly of 2.26 - Google couldn't find me one?
Putting a 16kB DFS ROM in a higher slot than the EEPROM (when loaded with DFS 2.26) allows it to boot so it is something to do with executing from EE. Has anyone had success with DFS 2.26 in EEPROM?
Indeed has anyone had success/problem with putting DFS 2.26 in an 64kB EPROM with other images?