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Possum Computer

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Possum is a z80-based 8-bit micro-computer emulator.

All peripherals are emulations of real-world hardware that was available in the 80s (or roughly 80s-adjacent).

The intent of the project is mostly a challenge for me to write as modern of an operating system and software for the excruciatingly minimal hardware available. (i.e. fun)

Rather than building this computer physically with a bunch of chips and a bread-board, the emulator stands as a more accessible and debuggable means of developing for the machine.

Goals

Hardware Emulation

  • z80 CPU
  • z8410 DMA (though not used yet since the timing emulation is a little sketchy)
  • 16550A UART
  • z80 CTC
  • 8-bit ATA drive(s)*
  • MOS 8563 VDC**

*2 disk images can be mounted on the ATA bus. The interface is Compact Flash actually, but it is 80s tech at its core.

**The 80-column display chip from the venerable Commodore 128! 16KB video RAM installed ;-)

Software (On Host)

Software (On Possum)

  • Monitor ROM with disk driver that can load the kernel: WIP
  • Filesystem (let's make a custom one!): WIP
  • Fuse driver for host access to the mount the filesystem
  • Banked memory-mapped IO
  • Preemptive multitasking (yes, really)
  • IPC
  • CP/M-compatability mode (a dream)
  • Text editor (vim-like)
  • z80 Port of PossumASM
  • SLIP ethernet driver
  • TCP/IP stack
  • ???

What's working

az65 z80 hello_hd.z80 > hello_hd.bin

possum-emu hello_hd.bin --hd0 blank.img

Model Name:	POSSUM-CF-CARD-EMULATOR-01
Serial #:	0-12345-67890-123456
Disk Size:	$00000080
Hello! Successfully wrote to the disk!