Cross-referenced with Linux 7.1 drivers/usb/host/xhci-ring.c
xhci_queue_isoc_tx() (lines 4055-4317).
trb.rs:
- Trb::isoch() — constructs Isoch Transfer TRBs (type=6).
Parameters: buffer, len, cycle, td_size, interrupter, isp,
chain, ioc, tlbpc (Transfer Last Burst Packet Count, bits 16-19),
sia_frame_id (Schedule In Advance / Frame ID, bits 20-31).
TLBPC=1 default (one packet per burst), SIA=0 default
(controller decides scheduling). ISP set for IN endpoints.
scheme.rs:
- Removed ENOSYS gate on isoch endpoints (~line 1704).
- transfer() branches on is_isoch: uses trb.isoch() for isoch
endpoints, trb.normal() for bulk/interrupt.
- bytes_transferred: for isoch, uses buffer length directly
(event.transfer_length() carries Frame ID, not remaining bytes
per xHCI spec §4.15.2 Transfer Event TRB).
- Error recovery: isoch codes (IsochBuffer, RingUnderrun,
RingOverrun, MissedService) fall through to no-retry in
maybe_recover_transfer_error — correct, isoch never retries.
This unblocks USB Audio Class (P6-C) and the redbear-usbaudiod
real driver (last remaining P1-D stub).
Red Bear OS
c89af69d08