Comments (3)
Important note: For some reason, it didn't occur to me that we still need to access the slot and switches when we're running the BIOS out of RAM. Figured out a hack wherein the high/low SRAM mapping is backwards from what it currently is between modes 0 and 2 and SRAM is selected in the ROM position in mode 2, but is otherwise the same. That way, when we start up in mode 0 we can copy the BIOS right into high physical SRAM and then switch into mode 2 running out of SRAM without really caring what physical portion of SRAM is mapped into the low cart area.
This is going to require some changes to both the PLD equations and the NES game loader code to work properly, which hasn't been implemented yet.
from nesii.
Fixed up and tested the PLD to match the aforementioned scheme
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Note to myself about RAM availability: ostensibly, once we're in NOS, we can switch to one of the all-RAM modes and switch in and out of mode 2 when we need to do disk access. That should give us gobs of room for things like BASIC if we're going to end up wanting it.
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Related Issues (20)
- [NES II] Read a sector HOT 4
- [NES II] Boot from a floppy HOT 2
- [NES II] Read and display the catalog from an Apple DOS 3.3-compatible disk HOT 2
- [NES II] Load and execute an Apple DOS 3.3 bin format executable HOT 8
- [NES II] Run NES game image from DOS filesystem HOT 4
- [NES II] Fix bottom line clearing during screen scroll HOT 1
- [NES II] Use check-for-data-changing floppy motor wait hack HOT 1
- [NES II] Add disk read timeout to bios HOT 2
- [NES II] Write a sector to a floppy
- [NES II] Implement a 'not an Apple II disk' warning in NOS boot code
- [NES II] Implement a 'not an Apple II program' warning in NES game loaders
- [NES II] Update SHELL to load any BIOS update modules found on the disk at startup HOT 1
- [NES II] Implement file create call
- [NES II] Implement file delete call
- [NES II] Implement file write call
- [NES II] Get BASIC running
- [NES II] Support execution of HELLO WORLD in BASIC
- [NES II] Support loading and running file from disk in BASIC
- [NES II] Support saving current file to disk in BASIC
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