Crt drive

crt-drive

Programmable CRT drive: sync and video from a microcontroller for analog CRTs and TVs.

The first target is the Link MC5 terminal (Wyse WY-120 architecture). A Raspberry Pi Pico (RP2040) replaces the CRT drive ASIC (Wyse 211009-02, U4): it synthesizes active-low /HSYNC and /VSYNC plus active-high dual video (V0 dim, V1 normal) and drives the existing deflection and neck boards. The original CPU, EPROM, and VRAM bus do not need to run.

Status: Injection pads and the Pico + 74AHCT125 carrier (KiCad protoboard) are decided. The Dev-Host Docker toolchain is validated (make smoke / make test APP=hello). Default firmware is the 60 Hz 80-col measure pattern (make build / make flash / make test / make monitor): GPIO 0–3, box+grid+plus; USB m 80/132-col, r 60/78 Hz; a/d/w/s nudge H/V phase. Four-mode analog drawings: make build APP=pattern. Phosphor reel: make build APP=demos (same m/r). Glass TTY: make build APP=term. CRT HIL is in progress after isolation and the 74AHCT125.

Docs

Dev-Host toolchain (Docker)

Edit on the Dev-Host. Firmware is compiled by calling into the pico-dev image from that host (make at the repository root); the repo is bind-mounted at /workspace for the call. Plug the Pico into this machine (no Raspberry Pi gateway). Modeled on fractalclockwork/cede lab/docker/pico-dev.

Full guide: docs/toolchains.md (setup, USB modes, hello_pico, troubleshooting). Short path: docker/README.md.

make image          # build crt-drive/pico-dev:local
make smoke          # ARM GCC, CMake, Ninja, Pico SDK, picotool USB
make pico-discover  # identify the Pico on this host's USB
make test APP=hello # build, flash, USB CDC ping (hello_pico)
make build          # 60 Hz 80-col plus (default CRT UF2)
make flash          # load crt_cross60
make monitor        # USB CDC; follows whichever app is running
make build APP=pattern
make build APP=term # glass TTY
make build APP=vtty # host session; usage in docs/vtty.md
uv sync             # Dev-Host .venv; Pillow for tools/vtty.py images
make vtty-start     # news page; make vtty-stop frees the serial node
make build APP=demos
make help           # all targets

make shell and make shell-usb are a call into the image. Leave with exit. The editor stays on the Dev-Host.

Phased development

Hardware is ready to drive: lift harness at pads V0, V1, V, H, GND; level-shift on the Pico carrier (74AHCT125); power from logic-board +5 V / GND. First video mode is 60 Hz 80-col (32.1 MHz dots, 1024-dot /HSYNC, 523 lines); USB m is 60 Hz 132-col (1188×416). 78 Hz patterns come after that raster is on-glass.

Firmware order (detail in firmware-plan.md):

1. Clock + PIO load — Pico PLL; 60 Hz in apps/cross60, 78 Hz in video/
2. Stable /HSYNC and /VSYNC — 60 Hz wraps 1024 dots / 523 lines (HIL); 78 Hz 1530 / 402 on a scope
3. Pixel SM + packing — 800×416 @ 2 bpp (60 Hz), 800×338 (78 Hz); FIFO stall, trailing off word
4. DMA loop into PIO TX — per-line kick from hsync RX
5. 60 Hz plus — default UF2; center and size on the live CRT (make test)
6. 78 Hz test patterns — make test APP=pattern after 60 Hz fills
7. Other apps — glass TTY in apps/term/; phosphor reel in apps/demos/

Safety

CRT anode and flyback voltages are lethal. Isolate U4 by lifting the harness wires at the labeled V0, V1, V, H, and GND pads before splicing in RP2040 signals. Do not work on a powered chassis until you know the discharge path for the CRT anode cap.