A version of the PZ1-system based on 65C02, Raspberry Pi Pico and 512KiB SRAM.
This is the second public release of SW and HW for the PZ1-project, now with some more bells and whistles.
The system uses my simple preemptive multitasking scheduler to manage the 512KiB RAM, using 16KiB for itself and system data.
The task switching does not waste many cycles. Every task gets its own stack and a full zero page, minus the 18 bytes used for OS-calls.
EhBASIC is running in a separate task with 64KiB RAM. There are added basic-commands to deal with tasks and the filesystem.
HW realised in the Pico:
- Serial communication via a virtual USB serial port.
- Serial port, 3.3V RX/TX on pin-header. Working but not used.
- SID-sound is based on TinySID, emulated on the second core of the Pico and mixed at 96000Hz, no SID-filters. 10-bit PWM-output on a single pin.
- IRQ-timer used by the scheduler, 16-bits.
- Frame counter registers, incremented @50Hz, 16-bits.
- HW/SW interfaces to filesystem operations.
- 4 bank registers, 16KiB memory blocks, the scheduler handles ownership of blocks.
The HW design is not the most efficient, mainly because the Pico lacks enough gpios to connect to the 65C02 and SRAM without buffers. The buffering is done with 74LVC-chips which adds complexity and lowers efficiency. The Pico and buffers are cheaper and more readily available than the faster and less complex Teensy 4.1.
Running the Pico at the standard 133MHz can run the 65C02 @1MHz. Overclocking the Pico to 250MHz can run the 65C02 @2MHz, just the way I intended. Using the PIOs would probably improve the performance.
I started the PZ1 project because I wanted to code 6502, build proper electronics hardware and investigate multitasking and bank-switched memory on a 6502-system. I also got back to designing proper PCBs, now in KiCad. I've done some iterations experimenting with:
- 6502 emulation or a real 65C02.
- Different MCUs: Teensy 4.0/4.1 / BluePill / Pico.
- External SRAM, RAM/ROM inside MCU, RAM on Teensy quad-SPI.
- Different sound emulation and output (PWM/I2S).
- 74-series glue logic / SPLD.
The ongoing work of PZ1 in general can be followed on my blog at hackaday.io
Use KiCad 6 to view/edit the schematics and PCB. There is also a PDF of the schematics.
Gerbers to build the 4-layer PCB are generated and available in a separate folder.
The Pico-socket in 3D-view of the PCB is not correct, too narrow.
A proper BOM is missing but here are the main components:
- 1x Raspberry Pi Pico
- 1x WDC65C02
- 1x AS6C4008, 512KiB SRAM
- 2x 74LVC244
- 1x 74LVC245
- 2x 74LVC373
- 2x 1x6 pin-header
- 2x 1x4 pin-header
- 1x 1x2 pin-header
- a bunch of decoupling capacitors
Use Arduino IDE with Earl Philhowers Pico board package, -O2 optimization.
The 6502-sources include pre-assembled h-files in the repository. Assembling on your own requires installation of the very fine assembler Jasm.
Run the asm.sh file to create the necessary h-files, along with a bunch of debug- and info-files.
Mail: adam.klotblixt@gmail.com