Rumbledethumps' Picocomputer 6502
The RP6502 is an 8-bit computer with VGA, Audio, and USB. It can be built entirely with through-hole components, compactly using surface mount devices, or even on a breadboard. No programming devices need to be purchased and the only component used that wasn't available in the 1980s is a $4/€4 Raspberry Pi Pico.
Join me on YouTube as I develop this project. https://www.youtube.com/channel/UC7kMjECYMyiSgFfiAm6c55w
Dev Setup
Standard Raspberry Pi Pico C SDK setup per the official docs; set PICO_SDK_PATH and PICO_EXTRAS_PATH, use cmake. The VSCode launch settings connect to a remote debug session. For example, I use a PicoProbe under WSL by passing the device to Linux with usbipd-win then bringing up a couple of terminals for the debugger and monitor.
PS> usbipd list
BUSID DEVICE
7-4 USB Serial Device (COM6), Picoprobe
PS> usbipd wsl attach --busid 7-4
$ sudo openocd -f interface/picoprobe.cfg -f target/rp2040.cfg -s tcl
$ sudo minicom -c on -b 115200 -o -D /dev/ttyACM0
Pi Pico - Power, CDC, and PicoProbe.
| #Pins | Description |
|---|---|
| 17 | VGA - 640x480 32768 colors |
| 2 | STDIO UART |
| 2 | SWD |
| 1 | PHI2 |
| 1 | RESB |
| 3 | PBUS |
Pi Pico - USB Host for Hub.
| GP# | Description |
|---|---|
| 0 | Chip Select |
| 1 | Write Enable |
| 2-9 | Data D0-D7 |
| 10-14 | Address A0-A4 |
| 15 | Bank A16 |
| 16-17 | STDIO UART |
| 18-19 | PWM Audio L-R |
| 20 | IRQB |
| 21 | PHI2 |
| 22 | RESB |
| 26-28 | PBUS |
Memory Map
| Addr | Description |
|---|---|
| FFFE-FFFF | BRK/IRQB |
| FFFC-FFFD | RESB |
| FFFA-FFFB | NMIB |
| FFF0-FFF9 | 10 bytes for fast load |
| FFE0-FFEF | 16 bytes for I/O TBD |
Fast Load
Self modifying RAM avoids some indirection. It's not much, so this may not happen if the resources are needed elsewhere, but it's worth trying for.
.org FFF0
loop:
LDA #00
STA $0000
BRA loop
JMP $0000