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EP0 control-OUT fix (usbtest 14/21, errno 110/-74): usbd queues the status-stage OUT ZLP of every control read with buffer=NULL, so the ISR's `if (out_buffer)` check missed it and marked the arriving ZLP as out_received instead. The stale flag poisoned the next control-OUT with data: its first chunk "completed" instantly from an empty EP0 buffer and the host's real DATA NAKed forever. Track queued transfers with an explicit out_queued flag and void half-finished control state on a new SETUP. Isochronous support (UM10562 12.15.6): 5-word DMA descriptors with per-packet size memory, buflen/present_count in packets, one packet per FRAME (no DMARSet/EpIntEn involvement), completion at EOT for both directions. Details that matter: - the iso machinery (5th DD word + packet-size memory) is compiled only when an iso-capable class is enabled (CFG_TUD_AUDIO/VIDEO/VENDOR), so non-iso builds pay nothing: _dcd stays 648 B vs 1032 B with iso - ISR dispatch keys on the hardware's fixed ep-number/type map (ep_id_is_iso), never on dd fields that thread mode rebuilds - iso OUT honors Packet_valid (bit 16) and prefills the hardware writeback slots with 0, so a missed frame counts as 0 bytes instead of reading back stale buffer contents as data - packet count is validated (tu_div_ceil <= ISO_MAX_PACKETS) before the DD is touched, so an oversized transfer is refused without leaving a serviceable half-built descriptor armed for the frame engine - dcd_edpt_iso_alloc and iso_activate both enforce the fixed iso endpoint numbers (3/6/9/12); classes ignore alloc's return value, so activate must not trust it Un-skip LPC40XX in the usbtest example; tier 4 now enumerates and passes iso cases 15/16/22/23. cdc_msc_throughput and printer_to_cdc had bulk on iso-only EP3 (SET_CONFIGURATION failed with -32); add the LPC17/40 EPNUM block (bulk on EP2/EP5) like other fixed-EP examples. Verified on ea4088_quickstart: usbtest tier-4 battery 30/30 repeatedly and the full device HIL suite 14/14 (incl. audio_test iso).
CDC + MSC Throughput
A deliberately minimal CDC + MSC composite device for measuring pure USB bulk throughput — the ceiling set by the USB link and the TinyUSB driver, with no backing storage or per-byte work in the way.
How it measures the ceiling, not storage
- MSC advertises a 1 GiB logical disk (2 Mi × 512-byte blocks) but has no real
backing store. Writes are discarded; reads zero-fill only the low LBAs the host
scans during enumeration (partition table / GPT header) and otherwise return
whatever is already in the transfer buffer — so no
memset/copy cost skews the result. - CDC drains its RX in
tud_cdc_rx_cband sources TX from a static zero filler, soddcan push data in either direction over/dev/ttyACMx.
The 1 GiB capacity lets dd run long enough for the rate to stabilise; high-speed peripherals show the most headroom.
USB Descriptors
| Interface | Class driver |
|---|---|
| 0–1 | CDC (virtual serial) |
| 2 | MSC (mass storage) |
Configuration
Notable tusb_config.h settings (tuned for throughput):
#define CFG_TUD_CDC 1
#define CFG_TUD_MSC 1
#define CFG_TUD_MSC_EP_BUFSIZE (TUD_OPT_HIGH_SPEED ? 4096 : 1024) // large MSC bulk buffer
#define CFG_TUD_CDC_RX_EPSIZE (TUD_OPT_HIGH_SPEED ? 2*512 : 2*64)
#define CFG_TUD_CDC_TX_EPSIZE CFG_TUD_CDC_RX_EPSIZE
#define CFG_TUD_CDC_RX_BUFSIZE (TUD_OPT_HIGH_SPEED ? 2*512 : 2*64)
#define CFG_TUD_CDC_TX_BUFSIZE CFG_TUD_CDC_RX_BUFSIZE
Building
CMake:
mkdir build && cd build
cmake -DBOARD=raspberry_pi_pico ..
cmake --build .
Make:
make BOARD=raspberry_pi_pico all
Measuring throughput (Linux)
The MSC disk appears as a raw block device (e.g. /dev/sdX); the CDC port as /dev/ttyACMx.
# MSC read (device → host)
sudo dd if=/dev/sdX of=/dev/null bs=1M count=256 iflag=direct
# MSC write (host → device, discarded)
sudo dd if=/dev/zero of=/dev/sdX bs=1M count=256 oflag=direct
# CDC read (device → host)
dd if=/dev/ttyACM0 of=/dev/null bs=64k count=4096
Pick the right
/dev/sdXcarefully — writing to the wrong block device destroys data.