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Patch TinyUSB CDC TX persistence bug - #19606

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dpgeorge wants to merge 3 commits into
micropython:masterfrom
dpgeorge:shared-tinyusb-patch-cdc-device
Open

Patch TinyUSB CDC TX persistence bug#19606
dpgeorge wants to merge 3 commits into
micropython:masterfrom
dpgeorge:shared-tinyusb-patch-cdc-device

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@dpgeorge

@dpgeorge dpgeorge commented Aug 12, 2026

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Summary

We recently updated to TinyUSB 0.21.0. At the time of updating we didn't realise that they changed how CDC TX persistence is configured -- from runtime configuration to a static macro configuration.

But in the process of changing that, and their updating to a new streams FIFO, the CDC TX persistence got broken.

This PR aims to patch that bug in tinyusb by applying a small .patch file as part of the build process:

  • exclude original cdc_device.c from the build
  • copy original cdc_device.c to build-BOARD/cdc_device.c
  • patch that file
  • add the patched file back to the build
  • build as usual

Both CMake (rp2 port) and make (everything else) are covered.

Testing

Tested on RPI_PICO and TEENSY40: the REPL banner now appears correctly after a hard reset (prior to this patch it was corrupted).

Trade-offs and Alternatives

This slightly complicates the build by patching during the build process.

Alternatives:

  • fork TinyUSB to fix it
  • wait for TinyUSB to fix it and release a new (patch) version
  • not fix it and accept that after a hard reset the REPL output is corrupt (and some chars are copied to the input stream)

Generative AI

I used Gemini to give me hints on how to wrangle CMake into getting this to work, but wrote everything myself.

@dpgeorge
shared/tinyusb: Use new static config for TX persistence.
f4e02f7 
The runtime config was replaced with simpler static macro config in TinyUSB
commit 222af862aa2b3898980e3ed8f28e70fe6c9a7ee9.

Signed-off-by: Damien George <damien@micropython.org>
@dpgeorge
shared/tinyusb: Add a patch for CDC TX persistence issue.
fd894b2 
See hathach/tinyusb#3807

Signed-off-by: Damien George <damien@micropython.org>
@dpgeorge dpgeorge added this to the release-1.29.0 milestone Aug 12, 2026
@dpgeorge dpgeorge added ports Relates to multiple ports, or a new/proposed port shared Relates to shared/ directory in source labels Aug 12, 2026
@codecov

codecov Bot commented Aug 12, 2026 •
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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.55%. Comparing base (b006887) to head (94c17a9).

Additional details and impacted files 
@@            Coverage Diff             @@
##           master   #19606      +/-   ##
==========================================
- Coverage   98.59%   98.55%   -0.04%     
==========================================
  Files         182      182              
  Lines       23320    23320              
  Branches        5        5              
==========================================
- Hits        22992    22984       -8     
- Misses        327      335       +8     
  Partials        1        1
Flag Coverage Δ
unix-coverage-32bit 98.55% <ø> (-0.05%) ⬇️
unix-coverage-64bit 98.52% <ø> (ø)

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@github-actions

github-actions Bot commented Aug 12, 2026 •
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Code size report:

Reference:  unix/mpconfigport: Use setjmp GC helper on macOS for Intel. [b006887]
Comparison: ports: Apply TinyUSB patch for CDC TX persistence. [merge of 94c17a9]
  mpy-cross:    +0 +0.000% 
   bare-arm:    +0 +0.000% 
minimal x86:    +0 +0.000% 
   unix x64:    +0 +0.000% standard
      stm32:    +0 +0.000% PYBV10
      esp32:    +0 +0.000% ESP32_GENERIC
     mimxrt:   -32 -0.008% TEENSY40
        rp2:   -16 -0.002% RPI_PICO_W
       samd:   -32 -0.012% ADAFRUIT_ITSYBITSY_M4_EXPRESS[incl -12(bss)]
  qemu rv32:    +0 +0.000% VIRT_RV32

@dpgeorge
ports: Apply TinyUSB patch for CDC TX persistence.
94c17a9 
Signed-off-by: Damien George <damien@micropython.org>
@dpgeorge
dpgeorge force-pushed the shared-tinyusb-patch-cdc-device branch from 27cd3af to 94c17a9 Compare August 12, 2026 03:20
@octoprobe-bot

octoprobe-bot commented Aug 12, 2026

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Octoprobe PR report

Test Tests
passed		 Tests
skipped		 Tests
xfailed		 Tests
failed
format flash 9 3
run-tests.py 16447 2571 15
run-tests.py --via-mpy --emit native 16212 2794 18 9
run-tests.py --via-mpy 13531 2217 12
run-perfbench.py 280 8
run-natmodtests.py 595 100 11
run-mpremote-tests.sh 21 6
run-tests.py --test-dirs=extmod_hardware 114 192 54
run-tests.py --test-dirs=extmod_hardware --emit-native 107 182 51
Total 47316 8067 161 15
Failures

Group: run-mpremote-tests.sh

Test stm32
7b21-
PYBV11-
DP
test_unicode.sh FAIL FAIL FAIL
test_mount.sh FAIL FAIL FAIL

Group: run-tests.py --via-mpy --emit native

Test mimxrt
1133-
TEENSY40		 nrf
3c2a-
ARDUINO_NANO_33		 rp2
5334-
RPI_PICO2		 rp2
5334-
RPI_PICO2-
RISCV		 rp2
552b-
RPI_PICO2_W		 rp2
5f2c-
RPI_PICO_W		 samd
5f2a-
ADA_ITSYBITSY_M0		 stm32
2b35-
NUCLEO_WB55		 stm32
7b21-
PYBV11		 stm32
7b21-
PYBV11-
DP		 stm32
3a21-
PYBV11-
DP_THREAD		 stm32
7b21-
PYBV11-
THREAD
extmod/machine_timer.py pass skip skip skip pass pass pass pass FAIL FAIL FAIL pass pass pass pass pass pass pass
micropython/viper_ptr8_load_boundary.py pass pass pass pass pass pass pass pass FAIL FAIL FAIL pass pass pass pass pass pass pass
stress/qstr_limit.py pass pass pass pass pass pass pass pass FAIL FAIL FAIL pass pass pass pass pass pass pass

@dpgeorge dpgeorge mentioned this pull request Aug 12, 2026
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@dpgeorge

dpgeorge commented Aug 12, 2026

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I made an alternative fix in #19607 which forks TinyUSB.

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