ESP32 I2S parallel channels - Compiler error because IsWriteDone() is not `const` ( NeoPixelBrightnessBus)

[softhack007]

Hi, I'm playing with the new I2S parallel mode, to see how it could be integrated into WLED.

I'm still on NeoPixelBrightnessBus and haven't changed to NeoPixelBusLg in my in-work version yet. So not sure if this problem happens with the depricated BrightnessBus only.

I'm running into a compile error, that seems to come because the IsWriteDone() method of NeoEsp32I2sXMethod is not const. Actually I can fix my build by adding const, however I'm not sure if this the right solution. Please advise.

https://github.com/Makuna/NeoPixelBus/blob/327b2d86d7902d7a73af24d1c6264028b495bcdb/src/internal/methods/NeoEsp32I2sXMethod.h#L472-L475

my humble workaround:

    bool IsWriteDone() const
    {

The code in WLED is a bit complicated, as we use void* to store arbitrary bus objects. Basically we do this:

#include "NeoPixelBrightnessBus.h"
#define B_32_I1X_NEO_3 NeoPixelBrightnessBus<NeoGrbFeature, NeoEsp32I2s1X8Ws2812xMethod>

void* busPtr = nullptr;
busPtr = new B_32_I1X_NEO_3(len, pins[0]);

static void begin(void* busPtr) { (static_cast<B_32_I1X_NEO_3 *>(busPtr))->Begin(); }              // works
static bool canShow(void* busPtr) { return (static_cast<B_32_I1X_NEO_3 *>(busPtr))->CanShow(); }   // compile error 

compile error:

In file included from .pio/libdeps/esp32_16MB_V4_M_debug/NeoPixelBus/src/internal/NeoMethods.h:54,
                 from .pio/libdeps/esp32_16MB_V4_M_debug/NeoPixelBus/src/NeoPixelBus.h:43,
                 from .pio/libdeps/esp32_16MB_V4_M_debug/NeoPixelBus/src/NeoPixelBrightnessBus.h:29,
                 from wled00/bus_wrapper.h:4,
                 from wled00/bus_manager.cpp:9:
.pio/libdeps/esp32_16MB_V4_M_debug/NeoPixelBus/src/internal/methods/NeoEsp32I2sXMethod.h: In instantiation of 'bool NeoEsp32I2sXMethodBase<T_SPEED, T_BUS, T_INVERT>::IsReadyToUpdate() const [with T_SPEED = NeoEsp32I2sSpeedWs2812x; T_BUS = NeoEsp32I2sMuxBus<NeoEspI2sDblBuffContext<NeoEspI2sMuxMap<unsigned char, NeoEspI2sMuxBusSize8Bit> >, NeoEsp32I2sBusOne>; T_INVERT = NeoEsp32I2sNotInverted]':
.pio/libdeps/esp32_16MB_V4_M_debug/NeoPixelBus/src/NeoPixelBus.h:138:40:   required from 'bool NeoPixelBus<T_COLOR_FEATURE, T_METHOD>::CanShow() const [with T_COLOR_FEATURE = NeoGrbFeature; T_METHOD = NeoEsp32I2sXMethodBase<NeoEsp32I2sSpeedWs2812x, NeoEsp32I2sMuxBus<NeoEspI2sDblBuffContext<NeoEspI2sMuxMap<unsigned char, NeoEspI2sMuxBusSize8Bit> >, NeoEsp32I2sBusOne>, NeoEsp32I2sNotInverted>]'
wled00/bus_wrapper.h:519:86:   required from here
.pio/libdeps/esp32_16MB_V4_M_debug/NeoPixelBus/src/internal/methods/NeoEsp32I2sXMethod.h:539:33: error: passing 'const NeoEsp32I2sMuxBus<NeoEspI2sDblBuffContext<NeoEspI2sMuxMap<unsigned char, NeoEspI2sMuxBusSize8Bit> >, NeoEsp32I2sBusOne>' as 'this' argument discards qualifiers [-fpermissive]
         return _bus.IsWriteDone();
                                 ^
.pio/libdeps/esp32_16MB_V4_M_debug/NeoPixelBus/src/internal/methods/NeoEsp32I2sXMethod.h:472:10: note:   in call to 'bool NeoEsp32I2sMuxBus<T_BUSCONTEXT, T_BUS>::IsWriteDone() [with T_BUSCONTEXT = NeoEspI2sDblBuffContext<NeoEspI2sMuxMap<unsigned char, NeoEspI2sMuxBusSize8Bit> >; T_BUS = NeoEsp32I2sBusOne]'
     bool IsWriteDone()
          ^~~~~~~~~~~
*** [.pio\build\esp32_16MB_V4_M_debug\src\bus_manager.cpp.o] Error 1

Evironment:

• NeoPixelBus 2.7.5, using NeoPixelBrightnessBus.h (not sure if it will happen with NeoPixelBusLg.h, too)
• platformio (platform = espressif32@ ~5.2.0)

  PLATFORM: Espressif 32 (5.2.0) > ESP32 16MB PACKAGES:

  • framework-arduinoespressif32 @ 3.20005.220925 (2.0.5)
  • tool-esptoolpy @ 1.40201.0 (4.2.1)
  • toolchain-riscv32-esp @ 8.4.0+2021r2-patch5
  • toolchain-xtensa-esp32 @ 8.4.0+2021r2-patch3

[Makuna]

Interesting, you are correct; that method should be marked const and it should not be compiling as is.

Will you create a pull with the change?

[softhack007]

yep, can do.

[Makuna]

https://github.com/Makuna/NeoPixelBus/releases/tag/2.7.6