julian
011fe5a4c4
The chunked-write fix (81bc2e3) still truncated on hardware: the lab
test slip stopped mid-sentence with no feed and no cut (text hidden
until the feed button). Verified against drivers/usb/class/usblp.c:
- write() returns at URB SUBMISSION, not completion;
- only ONE write URB is in flight (the next write EAGAINs until it
completes);
- usblp_release() — our close() — KILLS in-flight URBs.
The printer drains bulk data at PRINT speed (tiny internal buffer on
these clones), so closing right after the last accepted write cancels
the still-transferring tail — exactly where the feed + GS V cut bytes
live. Kernel-accepted ≠ printer-received.
Fix: the one-URB rule makes acceptance of write N a completion
certificate for write N−1. writeAllUsb now writes the payload's FINAL
BYTE alone — its acceptance proves everything before it is physically
in the printer — then drains 300 ms for that single packet before the
caller closes. New test pins the final-byte-alone chunking; wiki
printer-usb-transport.md carries the kernel-level account.
Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V