ESP32-P4 https://git.0x4200.cafe/esp32p4.git/atom?h=main 2026-08-26T12:24:17Z 2026-08-26T12:24:17Z Gabriel Schneider gbrls@0x4200.cafe 2026-08-26T12:24:17Z urn:sha1:ed8c5632e0228b1b821c87b511beb474c6a41f0c `zig build interact` did not compile. The mouse coalescer dated its held report with `std.time.milliTimestamp`, and this Zig's `std.time` has constants and `epoch` and no clock at all: the repo's own idiom is `std.Io.Timestamp`, already wrapped as `serial.Port.nowMs`, which is what the three call sites now use. The reason it survived every check I ran is worth writing down, because the same hole will swallow the next one. `zig build test` compiles `tools/console.zig` as a test module, and Zig only analyses what is REACHABLE: no test calls `attach`, so the loop containing the bad call was never looked at. Seven passing MouseFilter tests and a green `zig build test` said nothing whatsoever about whether the file compiles as part of an executable. Nor does plain `zig build` - p4-console is not in the default install step - so the only thing that would have caught it is building or running the named step, which is also the documented way to use this repo: `zig build interact -Dpardes`. Verified the way it should have been the first time: `zig build interact -Dpardes -Dcpu-mhz=360` with piped stdin flashes, attaches, takes the keystrokes and detaches at EOF. Also compiled every step's artifacts - elf, console, bench - and re-ran the matrix that matters for the editor side: default, Debug, ReleaseFast, ReleaseSafe, ReleaseSmall, and -Dplatform=p4 at Debug and ReleaseSmall, plus -Dp4-cols/-Dp4-rows at 40x12 and 80x24. Note for anyone reading a failing `zig build console` or `bench`: those RUN their tool, so they fail with DeviceBusy when something else is attached to the port. That is not a build error, and it is how this one hid in plain sight in the middle of the output. 2026-08-26T04:42:35Z Gabriel Schneider gbrls@0x4200.cafe 2026-08-26T04:42:35Z urn:sha1:cea01b8c08c30fa68fcbf18266937274a080507e ## The console thins mouse reports The board asks for DEC 1002, so the terminal reports presses, releases and motion while a button is held. A press is one report; a DRAG is one report per cell crossed, each about a dozen bytes. A hand crosses forty cells in a tenth of a second, which is ~500 bytes, which is 43 ms of a 115200 line - and every one of those bytes is input the board must parse while it is trying to paint the result of the previous one. Unthinned, a drag makes the editor unusable for as long as the drag lasts and for a while after. `MouseFilter` holds the newest motion report and drops the ones it supersedes, on a 40 ms window: ~25 reports a second, about 2.6% of the line. Newest-wins is right for motion and only for motion - where the pointer PASSED THROUGH is not information the editor can use, since a selection is defined by where the drag began and where it is now, so an intermediate report already stale by the time it reaches the wire is pure cost. Presses, releases and wheel notches are never held: each one means something different and dropping one loses a click. Ordering is the part worth testing. A held report is released before any non-motion byte that follows it, so a release cannot overtake the motion it ends, and a drag that stops moving still delivers its final position when the window expires. The seven tests cover those, a report split across a read boundary, a non-mouse escape sequence passing through untouched, and - the one that would hurt most - a lone ESC not being swallowed, because that is how you leave insert mode. ## Two hardware checks: p4-bench --check Both are regressions that no host test can see and no latency number can show. A lone Escape still leaves insert mode. The shell now holds a solitary ESC for 10 ms because on this wire the first byte of every sequence arrives alone; if that hold ever stops expiring, Escape stops working and the editor is unusable. A click split byte-by-byte lands at the column clicked. This is the bug that made the mouse look unimplemented, and it only appears when the bytes arrive separately - which the wire does anyway, 87 us apart. The check sends them as ten separate writes with no gap, because a gap longer than the hold would expire it and the check would be exercising nothing. Two things this file deliberately does NOT check, both because a check that cannot fail honestly is worse than no check. Input loss during transmit belongs to the deterministic host test in `src/pardes/input_rescue.zig`, which loses 67 bytes with the fix removed and needs no board. And every hardware oracle for it that was tried here was worse: the cursor stops being reported past 160 characters because the wrapped line outgrows the viewport, and a screen reconstruction cannot be rebuilt mid-session because the board only sends what changed. Both false starts are recorded in the file so the next person does not repeat them. The check also found its own bugs before it found any of the firmware's: 12 ms gaps between the click's bytes expired the very hold it meant to test, `$` produces no frame when the cursor is already at the end of the line, and reading the cursor after a press alone measures the revert rather than the click. 2026-08-25T17:38:25Z Gabriel Schneider gbrls@0x4200.cafe 2026-08-25T16:06:05Z urn:sha1:174991b8f3f8e9c792eede7a52ad7beb10a08b05 The editor arrives as one freestanding OBJECT exporting a seven-function C ABI (src/pardes/app.zig declares it, ../02-pardes-code/src/p4.zig implements it), not as a package dependency. A build.zig.zon path dependency was built first and reverted: merely DECLARING it nested pardes's ~30-package graph under this one and broke every build here - std/Build.zig:2091 exceeded its 1000-branch comptime quota via ghostty's lazyImport, seven cached tree_sitter versions use APIs removed in 0.16, and the fetch wrote 2.6 GB across 42,736 files into this working copy. The seam is bytes in and bytes out, which is what a serial line is anyway: the editor owns vaxis and the ANSI encoding, this side owns the UART, the heap and the clock, and neither names the other's types. It is versioned, because linkers do not type-check C symbols and a drifted signature would link cleanly and then corrupt the stack. THE BUG WORTH THE COMMIT. .flash.text was ALIGN(64), and the image builder's anchor makes two mapped segments share an MMU page safely - as long as rodata does not END inside the page where text BEGINS. With a 578 KB image it does. A volatile read of a string literal at 0x4004a1d1 returned 37 09 fa 4f, which disassembles to "lui s2, 0x4ffa0": this image's own .flash.text. Every literal in that last shared page read as code, so the first thing the firmware tried to print was machine code and it died on an instruction access fault. .flash.text is now ALIGN(0x10000), making the segments page-disjoint. The packing trick this project opened with only ever mattered when the alternative was 64 KiB of zeros in a 1 KB image. Two more findings, both recorded in README.md: * A linker symbol declared as an anyopaque OBJECT gives the optimiser a zero-sized object, so ordinary stores through a pointer derived from its address are dead code it may drop - and did, silently. The allocator's first block header read back as size=2988759312 next=0x14284684 and the free-list walk never terminated. @extern with a many-pointer has no size to lose. examples/memprobe.zig could not have caught it: it writes through a volatile pointer, which the optimiser must leave alone. * The RTC watchdog is armed at handover. Every example here had been resetting on a ten-second cycle, invisibly, because no run had ever lasted eight seconds. State, honestly: the firmware boots, clears .bss, brings up the console, disables the watchdog, starts the systimer, checks the ABI version, initialises the 384 KiB heap and calls into the editor, which sets up its sink and its environment. It then faults inside pardes_p4_init on the first allocation. The cause is measured but not fixed: a load from .flash.rodata page 3 returns the contents of the page 0x50000 higher - exactly the vaddr distance between the rodata and text segments - while pages 0, 2 and 4 read correctly. The bisect markers that localised it are still in place, deliberately, because the next step needs them. --- correction, measured after the above was written --- Two mapped segments is NOT a choice, and the earlier comment in tools/image.zig was right for a reason I initially got wrong and then measured. I first read bootloader_utility.c's `#else` branch, which classifies segments by address window with two independent ifs - and since the P4's DROM and IROM windows are the identical range (soc.h:146-149), I concluded the last mapped segment wins both roles and the first is never mapped. That branch does not run on this chip. The P4 takes the SOC_MMU_DI_VADDR_SHARED branch (bootloader_utility.c:805-851), whose own comment says it: "On chips with shared D/I external vaddr, we don't divide them into either D or I, as essentially they are the same." It collects mapped segments POSITIONALLY into rom_addr[2] and ends with assert(rom_index == 2); Shipping a one-segment image proved it, on the board: Assert failed in unpack_load_app, bootloader_utility.c:842 (rom_index == 2) So the split stays, image.zig keeps enforcing exactly two - turning that boot-time abort into a build-time error - and both are now documented with the branch that actually runs and the assert that actually fires. What DOES change is alignment. .flash.text was ALIGN(64). Two mapped segments may share a 64 KiB MMU page only if they also share a flash page, which the image builder's anchor guarantees - and that holds right up until an application is large enough for rodata to END inside the page where text BEGINS. With a 578 KB image it does. Measured on the die: a volatile read of a string literal at 0x4004a1d1 returned 37 09 fa 4f, which disassembles to "lui s2, 0x4ffa0" - this image's own .flash.text. Every literal in that shared page read as code, so the first thing the firmware tried to print was machine code, and it died on an instruction access fault. .flash.text is now ALIGN(0x10000), which makes the segments page-disjoint. It costs up to 64 KiB of image padding against a 1.5 MiB partition; the packing trick this project opened with only mattered when the alternative was 64 KiB of zeros in a 1 KB image. With that fixed the firmware gets much further: entry, .bss cleared, console up, watchdog disabled, systimer running, ABI version checked, the 384 KiB heap initialised, into the editor, its sink and environment ready - and the literal at 0x4004a1d1 now reads back correctly. Still open, and characterised rather than guessed: pardes_p4_init faults on its first allocation. The allocator struct crosses the seam intact (its function pointers land in .flash.text), but the std.mem.Allocator vtable at 0x40035a1c reads back as instruction bytes, and the dispatch at .flash.text+0xade2 jumps through it. Ruled out with measurements: the ELF and the image agree at that address, the flash is MD5-verified against the image, the wrong bytes are identical across three resets and two reflashes (so not a stale cache), the corruption is a contiguous run rather than 64-byte lines, and mmu_hal_map_region's arithmetic (page_num = ceil(len/page), entry from vaddr) is correct for the segments as now laid out. The next measurement is the one that settles it: read the MMU entry registers from the running application and print vaddr -> flash for every page. The register model in src/soc.zig can do that; the bisect markers are left in place for it.