Useful 6502 Machine

The goal of this project is to build a 6502-based portable machine, running my own operating system.

Current Status

See the complete implementation plan and progress here: Implemementation Plan

PCB assembled, blinky light on PIC is working.

Hardware Goals

These are some general points; for the full hardware specification, see here: Hardware Specification

I want the following end goals to categorize the machine as "useful":

• At least 2 Megabytes of program memory and 2 Megabytes of data memory, of which at least 16k of memory can be used by a single process.
• Protected memory (kernel and user run modes defined by hardware checking if kernel or user code is being executed)
• PIC16 as peripheral coprocessor for fast i/o

Software Goals

• Traps via "BRK" instruction for sys calls
• Full preemptive multitasking with up to 255 processes, round robin scheduler (maybe mlfq eventually)
• Filesystem: Tree, leaf nodes are devices or drivers.
• Driver for FAT32-formatted SD cards for easy file storage & transfer
• Standard library compatible with cc65 for creating high-level programs
• Basic UNIX-like shell utilities
• Simple web browser?
• SSH client based on DropBear?

Faults

Faults will be detected by hardware and trigger a RESET, and the kernel will terminate the process.

Hardware Timers

A hardware timer using the 65c22 will be used to interrupt processes with an NMI. The kernel will maintain a global clock for user timing needs.

The PIC peripheral coprocessor may, perhaps, feature a watchdog timer to restart the kernel in the event of a crash.

Particularly Helpful References

There are many resources that have proven themselves indispensible to the progress of his project.
Here is a small subset of such resources:

• https://www.pagetable.com/c64ref/6502/#
• http://www.6502.org/users/andre/index.html
• https://wilsonminesco.com/
• https://www.burtonsys.com/ps2_chapweske.htm
• https://www.pagetable.com/?p=1416
• https://github.com/commanderx16/x16-rom/