# FreeDOS on TTGO VGA32 (ESP32, FabGL 8086 emulator)

Sketch `dosvga32/`: FabGL 1.0.9 `Machine` (i8086, PIC, PIT, i8042, MC146818, CGA/Hercules adapter, embedded BIOS
`biosrom.h`) from the PCEmulator example, copied locally and modified. No SD, WiFi or BT.

## Build
    export PATH=/tmp/opencode/w:$PATH ARDUINO_DIRECTORIES_DATA=/tmp/opencode/ard ARDUINO_DIRECTORIES_USER=/tmp/opencode/ardu
    arduino-cli compile -b esp32:esp32:esp32:FlashMode=dio,FlashFreq=40 --build-path /tmp/b --jobs 4 dosvga32
    # merge: see esptool merge_bin command in the task (0x1000 boot, 0x8000 parts, 0xe000 boot_app0, 0x10000 app, 0x200000 dosdisk.img)
`dosvga32/partitions.csv` is picked up automatically (PSRAM option must stay Disabled; the code calls esp_spiram_init itself).
Extra QEMU test build: add `--build-property build.extra_flags=-DDOSVGA_NO_VIDEO` (skips VGA mode switching, which hangs in QEMU).

## Flash layout (4 MB)
| offset | size | content |
|---|---|---|
| 0x1000 | | bootloader |
| 0x8000 | 0x1000 | partition table |
| 0x9000 | 0x5000 | nvs |
| 0xe000 | 0x2000 | otadata (boot_app0.bin) |
| 0x10000 | 0x1F0000 | app0 (ota_0, ~490 KB used) |
| 0x200000 | 0x168000 | `dosdisk` (data, subtype 0x40) = raw 1.44 MB FreeDOS 1.4 floppy `144m/x86BOOT.img` |

## Pins (FabGL defaults = VGA32)
VGA R=22,21 G=19,18 B=5,4 HS=23 VS=15; PS/2 keyboard CLK=33 DATA=32; mouse CLK=26 DATA=27; audio 25.
SD pins unused (MCP23S17 SPI probing removed).

## Disk access
`diskpart.cpp` finds partition `dosdisk` (esp_partition_find_first) and exposes it as a `FILE*` via `fopencookie`
for drive A: (fd0, geometry autodetected 80/2/18). Reads use `esp_partition_read`; writes go to a RAM overlay
(copy-on-write 512 B sectors, 1 MB pool in the unused upper half of the emulated-RAM PSRAM block), lost at reset.

## Notes
* Needs PSRAM (1 MB emulated PC RAM at 0x3F800000, as in FabGL PCEmulator). VGA32 v1.4 (WROVER) has it.
* Video: FabGL GraphicsAdapter -> VGADirectController (64 colours); text = 640x480@60 with 640x400 viewport (80x25, 8x16), Hercules = 720x350@70.
* Serial 115200 logs: stages + heartbeat with emulated instruction count and CS:IP.
* dist/: `dosvga32.flash.bin` (real HW), `dosvga32.novideo-qemu.flash.bin` (QEMU test), `hello.flash.bin`.
* QEMU: `qemu-system-xtensa -nographic -machine esp32 -m 4M -global driver=ssi_psram,property=is_octal,value=false -drive file=F,if=mtd,format=raw` (PSRAM needs these flags).

## Extra notes (emulator project)

- `dist/dosdisk.img` is the FreeDOS 1.4 boot floppy with `FDCONFIG.SYS` (menu timeout 1 s) and `FDAUTO.BAT` (installer step replaced by a banner) patched so the demo reaches `A:\>` quickly; the untouched floppy is `dist/dosdisk.orig.img`.
- `vgademo/` (FabGL VGA16 + PS/2 keyboard echo) and `echo/` (Serial echo + LED on GPIO2) are the two extra example sketches.
- Build all sketches with `arduino-cli compile -b esp32:esp32:esp32:FlashMode=dio,FlashFreq=40` (core esp32@2.0.17, FabGL@1.0.9), then merge with `esptool.py merge_bin --fill-flash-size 4MB ...` (see `../tools`).