init writes /mnt/usb/DANOS.LOG at shutdown and then enters S5 — but the write sat in the USB flash controller's write cache and was lost when power was cut, because nothing issued SCSI SYNCHRONIZE CACHE. Invisible in QEMU (its backing file commits immediately); real on hardware. The boot-time flush survived only because the machine kept running afterward and the cache drained on its own.
- block protocol gains a flush op; usb-storage serves it with SYNCHRONIZE CACHE (10); runtime.block gains Device.flush()
- the FAT server tracks whether blocks were written and, on a file close, commits the device cache (durable-on-close — the right default for removable media, and it makes init's existing shutdown close() persist the log before S5, no init/VFS change needed)
- verified the SYNCHRONIZE CACHE actually reaches the driver on each dirty close; usb-storage/fat-mount/mutations/rename/mtime/log-flush all green
Flesh out the xHCI host-controller driver into a full transfer engine and build
the three USB class drivers on top, all verified end to end under QEMU.
- xHCI engine (usb-xhci-library.zig): controller reset, command/event rings with
cycle-bit bookkeeping (gated on a No-Op-command proof), device slots, Address
Device, control transfers, full chapter-9 enumeration, Configure Endpoint, and
interrupt/bulk transfers. Each interface is device_registered with its
(class,subclass,protocol) identity, unique per (port,interface).
- Bus<->class transfer protocol (usb-transfer-protocol.zig + runtime.usb): open /
control / interrupt-subscribe (async report pump on a poll timer) / bulk-by-
physical-address, so sector data never crosses the 256-byte IPC limit.
- USB HID keyboard + mouse (usb-hid/): decode boot-protocol reports and publish
to the input service. A USB usage is already the input protocol's keycode.
- USB mass storage (usb-storage/): Bulk-Only Transport + transparent SCSI,
serving a block device under the new .block service id (block-protocol).
- device-manager matches USB interfaces to class drivers (usbDriverForIdentity).
- usb-abi / usb-ids made importable modules; add HID and mass-storage class
requests, packTriple, and a usb_device DeviceClass.
- Fix test/qemu_test.py on macOS: the QMP unix-socket path was built from the
deep worktree path and exceeded the 104-byte sun_path limit, so QEMU exited
before booting. It now lives under a short temp path.
Tests: usb-report, usb-hid, usb-storage pass under python3 test/qemu_test.py;
host units (usb-abi, usb-ids, hid-report, bulk-only-transport, scsi) green.
Daniel Samson