From 939e3a7288d6782139cac36f091ccd1d41cdfc0a Mon Sep 17 00:00:00 2001 From: Gabriel Schneider Date: Tue, 25 Aug 2026 13:01:13 -0300 Subject: A fourth platform: pardes as ESP32-P4 firmware, bytes in and bytes out `-Dplatform=p4 -Dtarget=riscv32-freestanding` emits a single freestanding OBJECT exporting a seven-function C ABI, not an executable. The board's toolchain (../05-zig-p4) owns `_start`, the linker script and the UART driver and links this in. The seam is bytes rather than types, so neither side can accidentally depend on the other's internals, and a signature that drifts fails at link time. The serial line is the whole of the I/O. `src/p4.zig` drives vaxis unchanged over it: the renderer is a byte writer and `queryTerminalSend` is a byte writer, so the terminal emulator on the host answers the capability handshake and the firmware sees a real terminal. Measured going out over the wire on attach: alt screen, in-band resize, cursor report, kitty keyboard, kitty graphics, DA1. THREE WORDS EXIST ONLY HERE. `src/board_memory.zig` implements `Peek`, `Poke` and `Hexdump`, gated on `builtin.os.tag == .freestanding and !isWasm()` - derived from the TARGET, because they are a property of running with no OS under you rather than a product option, and because wasm is freestanding too and is exactly what must be excluded: in a browser an address is an offset into the linear memory this editor's own heap lives in. Every access goes through `*allowzero volatile`: a peripheral register is not memory, and address 0 is an ordinary unmapped address on this bus. One 4 KiB cap per command, set by the console rather than the memory - an unbounded dump would wedge the only console the board has for eleven hours. Measured on ESP32-P4 rev v1.3 silicon, driven from a host terminal: Peek 0x501101a4 0x0e63ce71, then 0xaeaa6919 on a second read - the RNG register, so the volatile loads are not folded Poke 0x5011002c 0xdeadbeef LP_STORE0; a later Peek returned 0xdeadbeef Hexdump 0x5011002c 32 16 bytes a row, hex columns and an ASCII gutter Peek 0x50110001 `peek: MisalignedAddress` on the message row That last line is the one that matters. A misaligned 32-bit access traps, and a trap in firmware is a watchdog reset that takes the session with it, so the check that turns it into a message is the reason the file is hand-written rather than a generic reader. BARE METAL BOOTS AN EMPTY OUTPUT BUFFER. Every other boot layout in `init` makes a shell, and on this platform that is not a preference but an impossibility: nothing to fork, no pty to give a terminal pane. Booting one anyway produced precisely what that describes - a pane whose tag ends in `Filter`, no gutter, no buffer, and every keystroke vanishing into the Fallback's silent pty. An output buffer is also what the platform's own words want, since Peek, Poke and Hexdump each fill one. Sized for the board rather than for a desktop: * `allocators.zig` gains a p4 tier that is ALL fallback - every capacity is zero, so each arena spills immediately to the 384 KiB heap the firmware hands over, and no megabyte-shaped static reservation lands in `.bss`. * `source_manifest.zig`'s allowlist is EMPTY on p4. The table is ~0.95 MiB of rodata against a 1.5 MiB flash partition; the firmware's filesystem is the serial host's, through the Host vtable. * The grid is clamped and the clamp is measured, not guessed: every cell is paid for four times (vaxis Screen + InternalScreen, pardes Surface + previous_cells), so 40x12 fits and 80x24 exhausts the heap during `Pardes.init`. * `Vaxis.resize` deinits both screens before allocating replacements, so a failed resize leaves vaxis rendering nothing. The p4 shell keeps the previous geometry on failure instead of leaving a half-applied one. Also here: `output_pane_integration_test.zig` had an exhaustive switch over `Platform` that adding `.p4` left unhandled, which broke `zig build unit-test` outright - the native test binary is the one consumer no platform build compiles. 346 tests pass again. --- src/dump.zig | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) (limited to 'src/dump.zig') diff --git a/src/dump.zig b/src/dump.zig index 566cf03c..37ba83c0 100644 --- a/src/dump.zig +++ b/src/dump.zig @@ -42,7 +42,16 @@ pub const max_panes: usize = 16; pub const max_cols: usize = 6; /// Bounds the only user-editable, schema-owned tag fragment. Keep this beside /// the dump limits so readers can reject data before copying it into a pane. -pub const max_tag_tail: usize = 4096; +/// It IS the storage bound: `Pane.tag_tail` is `[max_tag_tail]u8`, and every +/// writer (appendTag, tagInsert, restoreDumpTail, the acmefs `tag` file) +/// refuses input that does not fit rather than truncating it, so the schema +/// limit and the buffer can never disagree. +/// +/// 512 on the P4 firmware. A tag is ONE line — a pane's path plus its command +/// words — and 4 KiB of it is 4 KiB per pane out of a 384 KiB heap. A serial +/// console is 80 columns; 512 is six of those. +pub const max_tag_tail: usize = + if (@import("pardes_config").platform == .p4) 512 else 4096; /// Output arguments are typed in the same bounded one-line tag storage. Keep /// the schema limit named independently so a dump reader can validate it /// without importing the output-pane implementation. -- cgit v1.3