From 4656a1003226709e9b3c804ec32b4913fca4c7f4 Mon Sep 17 00:00:00 2001 From: user Date: Thu, 16 Jul 2026 13:54:23 +0200 Subject: term: 40-column text terminal on the CGB LCD (4x8 dynamic tiles) Add a background-tile text terminal that packs TWO 4px-wide characters into each 8x8 tile, giving a 40x18 grid instead of the 20x18 you'd get from an 8x8 font. The tilemap is static (one dedicated VRAM tile per screen position); we rebuild a tile's 16 bytes from two glyphs whenever a character changes. 360 tiles exceed the 256 a single tilemap can address, so positions 256-359 live in VRAM bank 1 via the CGB tilemap attribute bank-bit -- hence CGB-only. - Switch the ROM to CGB (rgbfix -C). Safe for the FS: every process has PROC_WRAMB=1, so SVBK stays on bank 1 and the WRAMX FS caches don't move. - CGB BG palette 0 = white bg / black text via BCPS/BCPD. - src/term.asm: term_init (palette + static tilemap + clear buffer), build_tile (combine two 4px glyphs -> one 8x8 tile, correct VRAM bank), term_redraw (rebuild all tiles), term_puts, term_show, term_test. - src/font.asm: 96-glyph 3x5-in-4x8 font, generated by tools/genfont.py. - 40x18 text buffer at $D600 (WRAMX, above the FS caches). - tools/ppmview.py: render a --shot PPM as ASCII so the LCD is inspectable from the shell during development. Verified via emulator screenshot: "GBOS TERMINAL", the alphabet, and a bank-1 row all render legibly at 40 columns. Serial shell + filesystem still work unchanged. Note: a full term_redraw builds 360 tiles and takes ~8 frames; fine for incremental single-char updates, but scrolling needs a smarter path (next milestone). Input (no keyboard) is also still TODO. --- src/boot.asm | 2 ++ 1 file changed, 2 insertions(+) (limited to 'src/boot.asm') diff --git a/src/boot.asm b/src/boot.asm index 9d9571e..0a5f2e3 100644 --- a/src/boot.asm +++ b/src/boot.asm @@ -56,6 +56,8 @@ KernelInit: ld a, HIGH(wKernelPCB) ld [wCurProc+1], a call fs_init ; mount the disk (format on first boot; persists) + call term_init ; set up the LCD text terminal + call term_test ; render a test pattern ; --- spawn the init task (pid 1); it fork()s the rest --- ld hl, TaskInit -- cgit v1.3.1-sl0p