mirror of
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4b1c8d16f7
Documentation tooling:
- Add the `build-doc` skill and `tools/build_doc.py` wrapper for local
Sphinx builds (clean / -W / open).
- Enable Markdown (MyST) in conf.py and auto-collect
examples/{device,host,dual}/*/README.md into a 3-level Examples nav
(Examples > Device/Host/Dual > example), noting each page's source
location and normalizing headings to a single H1.
- Remove the stale `.claude/commands/build-doc.md`; point the AGENTS.md
Documentation section at the skill.
Example docs:
- Add a README.md for every device/host/dual example: what it does, USB
interface table, notable tusb_config.h settings, generic CMake + Make
build steps, and how to try it.
- Fold each *_freertos variant into its base README, noting the FreeRTOS
source path and any RTOS-specific behavior.
Generated docs/examples/ output is git-ignored. Builds clean with
`sphinx-build -W`.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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.