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[upstream backport] RMT High-priority Interrupt driver - solves flickering problems on esp32, esp32-S2 and esp32-S3 #308

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Merged
softhack007 merged 16 commits into from
Jan 9, 2026
Merged

[upstream backport] RMT High-priority Interrupt driver - solves flickering problems on esp32, esp32-S2 and esp32-S3 #308

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abdbe0b
Merge pull request #4980 from willmmiles/0_15_x_rmthi
willmmiles Oct 5, 2025
4c6b352
upgraade all esp32 buildenv to NeoPixelBus 2.7.9
softhack007 Jan 5, 2026
86473a8
RMTHI backport to NPB 2.7.9
softhack007 Jan 5, 2026
8d41bc4
don't compile RMTHI on unsupprted (old) platforms
softhack007 Jan 5, 2026
d70a3a8
additional protection
softhack007 Jan 5, 2026
fafcbf9
no file access waiting if we have the flicker-free LEDs driver
softhack007 Jan 6, 2026
ad04097
WLEDMM_NO_FILEWAIT => WLEDMM_FILEWAIT
softhack007 Jan 6, 2026
cec6e22
small simplification
softhack007 Jan 6, 2026
3af8987
disable RMTHI on -S2
softhack007 Jan 6, 2026
d1d020b
disable RMTHI on -S3
softhack007 Jan 6, 2026
68eee6b
re-enable RMTHI for debugging, simplified buildenv for deugging
softhack007 Jan 7, 2026
dc10a76
(minor) fix for WLED_RELEASE_NAM
softhack007 Jan 7, 2026
01331b2
Merge branch 'mdev' into flickerFixer_backport
softhack007 Jan 7, 2026
db847f5
make sure that the interrupt driver is compiled
softhack007 Jan 8, 2026
74a8a95
-S3 and -S2 work with RMTHI now
softhack007 Jan 8, 2026
5ce9ba6
finishing touches and cleanup
softhack007 Jan 9, 2026
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2 changes: 2 additions & 0 deletions lib/NeoESP32RmtHI/include/NeoEsp32RmtHIMethod.h
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,7 @@ License along with NeoPixel. If not, see
#pragma once

#if defined(ARDUINO_ARCH_ESP32)
#if !defined(WLED_USE_SHARED_RMT) && !defined(__riscv) && (ESP_IDF_VERSION_MAJOR >= 4) // WLEDMM don't compile this file on unsupported platforms

// Use the NeoEspRmtSpeed types from the driver-based implementation
#include <NeoPixelBus.h>
Expand Down Expand Up @@ -485,3 +486,4 @@ typedef NeoEsp32RmtHI7Ws2805InvertedMethod NeoEsp32RmtHI7Ws2814InvertedMethod;
#endif // !defined(CONFIG_IDF_TARGET_ESP32C3)

#endif
#endif
2 changes: 2 additions & 0 deletions lib/NeoESP32RmtHI/src/NeoEsp32RmtHI.S
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Expand Up @@ -6,6 +6,7 @@
*/

#if defined(__XTENSA__) && defined(ESP32) && !defined(CONFIG_BTDM_CTRL_HLI)
#if !defined(WLED_USE_SHARED_RMT) && !defined(__riscv) && defined(ARDUINO_ARCH_ESP32) && (ESP_IDF_VERSION_MAJOR >= 4) // WLEDMM don't compile this file on unsupported platforms
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@willmmiles willmmiles Jan 8, 2026

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This line is the cause of your problems: the high priority interrupt assembly layer is being disabled here. Neither ARDUINO_ARCH_ESP32 or ESP_IDF_VERSION_MAJOR are available as they haven't been included, only command-line defines are available at this point in the file. (Also !defined(__riscv) is implied by defined(__XTENSA__)).

(FWIW the !defined(CONFIG_BTDM_CTRL_HLI) check there above is also wrong -- it can never be defined at that point in the file since sdkconfig.h hasn't been included yet.)

This change is also unnecessary: the linker will discard the object file if it's never referenced by the application code. (This is the same approach used by all the other unused drivers in NPB.)

The error isn't caught at build time because the NeoESPRmtHIMethod.cpp code that asks for it to be linked is playing some games with __attribute__((used)) in a way that cues the linker to include the file, but at no actual code space or runtime cost. However, if the assembly file is missing, the link will still succeed as the symbol it calls for is never in fact truly used. I'd prioritized runtime performance over developer convenience - sorry about that!

Anyways my recommendation is revert all the changes to lib/NeoESP32RmtHI from this patch. If bus_wrapper.h never calls for any RMTHI instances, the linker will discard the .cpp and .S object files, so it ultimately won't affect any build products.

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@willmmiles willmmiles Jan 8, 2026

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If you're curious as to the derivation of the symptoms:

  • Tasmota ESP32 (no suffix) cores include CONFIG_BTDM_CTRL_HLI, so the HI driver piggybacks on the Bluetooth driver's handler (as there's only one high priority interrupt level available). This is why it worked on basic ESP32s, but not -S2s and -S3s.
  • Without the contents of the .S file from the library, the linker falls back to the default highint handler (a no-op). So as soon as an RMT interrupt was generated, the core in question looped forever, as the interrupt would never be cleared.

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@softhack007 softhack007 Jan 8, 2026

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This line is the cause of your problems: the high priority interrupt assembly layer is being disabled here. Neither ARDUINO_ARCH_ESP32 or ESP_IDF_VERSION_MAJOR are available as they haven't been included, only command-line defines are available at this point in the file. (Also !defined(__riscv) is implied by defined(__XTENSA__)).

wow, that's unexpected, but it explains the problems. I still have a problem with my "emergency fallback" esp32dev_compat V3 buildenv, because its still on NPB 2.7.5.

Compiling .pio\build\esp32dev_compat\src\wled00.ino.cpp.o
Linking .pio\build\esp32dev_compat\firmware.elf
.pio\build\esp32dev_compat\libafb\NeoESP32RmtHI\NeoEsp32RmtHI.S.o:(.iram1.literal+0x14): undefined reference to `NeoEsp32RmtMethodIsr'
.pio\build\esp32dev_compat\libafb\NeoESP32RmtHI\NeoEsp32RmtHI.S.o: In function `_highint_stack_switch':
(.iram1+0x92): undefined reference to `NeoEsp32RmtMethodIsr'
collect2.exe: error: ld returned 1 exit status

--> i'll do some more experimenting, most likely I can still protect compiling the .s file with #if !defined(WLED_USE_SHARED_RMT) because this is a command line define.

😅 means another round of testing, but at least we now have an explanation that makes sense 👍

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@willmmiles willmmiles Jan 8, 2026

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Maybe try lib_ignore = NeoESP32RmtHI in the environment def for those using older NPB? It might be cleaner.


#include <freertos/xtensa_context.h>
#include "sdkconfig.h"
Expand Down Expand Up @@ -260,4 +261,5 @@ ld_include_hli_vectors_rmt:


#endif // CONFIG_BTDM_CTRL_HLI
#endif // WLEDMM
#endif // XTensa
2 changes: 2 additions & 0 deletions lib/NeoESP32RmtHI/src/NeoEsp32RmtHIMethod.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@ License along with NeoPixel. If not, see
#include <Arduino.h>

#if defined(ARDUINO_ARCH_ESP32)
#if !defined(WLED_USE_SHARED_RMT) && !defined(__riscv) && (ESP_IDF_VERSION_MAJOR >= 4) // WLEDMM don't compile this file on unsupported platforms

#include <algorithm>
#include "esp_idf_version.h"
Expand Down Expand Up @@ -504,4 +505,5 @@ esp_err_t NeoEsp32RmtHiMethodDriver::WaitForTxDone(rmt_channel_t channel, TickTy
return rv;
}

#endif
#endif
2 changes: 1 addition & 1 deletion wled00/bus_wrapper.h
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Expand Up @@ -184,7 +184,7 @@ bool canUseSerial(void); // WLEDMM (wled_serial.cpp) returns true if Serial ca
#endif


// RMT driver selection
// RMT driver selection - only for Xtensa and ESP-IDF 4.x
#if !defined(WLED_USE_SHARED_RMT) && !defined(__riscv) && defined(ARDUINO_ARCH_ESP32) && (ESP_IDF_VERSION_MAJOR >= 4)

#include <NeoEsp32RmtHIMethod.h>
Expand Down