This is a simple emulator designed to help bring up Fuzix on the BBC Matchbox co-processor with banked RAM. At this point we don't try and emulate the wait states on the external RAM but just run at about 4MHz.
The 6502 emulator is from MoarNES by Mike Chambers.
GNU GPL v2.
8K banked memory with bank registers selecting 8K pages from a 1MB RAM range (128 banks) using bank identifiers 0-7. Memory between FE00-and FFEF is mapped to I/O space always while FFF0-FFFF map to the RAM.
On boot the bank registers are 0,1,2,3,4,5,6,7.
I/O space is 0xFE00 plus
| Address | R/W | Description |
|---|---|---|
| FE00-7 | r/w | Bank number |
| FE10 | ro | Timer int clear (reports interrupts since last) |
| FE20 | r | Next input byte |
| FE20 | w | Output byte |
| FE21 | ro | Input status (bit 0 - input pending bit 1 - write ready) |
| FE30 | r/w | Disk number |
| FE31 | r/w | Block high |
| FE32 | r/w | Block low (512 byte blocks) |
| FE33 | w | Trigger disk action (sets diskstat, uses disk/block) |
| FE34 | r/w | Read or write next byte |
| FE35 | ro | Disk status (clear on read) |
| FE40 | w | Write 0xA5 to halt system |
The imaginary boot ROM loads block 0 from disk to $FC00 and jumps to it.
Currently one large disc is implemented. It's meant to provide a simple API akin to that we'll have calling through the tube firmware.