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Off-by-one Error In RMT Example #2921

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tedhenry100 opened this issue Jun 23, 2019 · 1 comment · Fixed by #2986
Closed

Off-by-one Error In RMT Example #2921

tedhenry100 opened this issue Jun 23, 2019 · 1 comment · Fixed by #2986

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@tedhenry100
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In https://github.com/espressif/arduino-esp32/blob/master/libraries/ESP32/examples/RMT/RMTWriteNeoPixel/RMTWriteNeoPixel.ino lines 64 and 65 there is an off by one error.

The shift is too much. for the first iteration of the loop 1<<(8-0) is 100000000 which is not the desired bit mask. The desired bit mask is 1000000. It should be 1<<(7-0)

        for (bit=0; bit<8; bit++){
            if ( (color[col] & (1<<(8-bit))) && (led == led_index) ) {

There is a comment from @VerusLogic in the related commit about this problem.

4e96bff#diff-e59a7abf6f432b9f3d716a15f5f9b715

@david-cermak
david-cermak added a commit to david-cermak/arduino-esp32 that referenced this issue Jul 14, 2019
@david-cermak
RMT: Fix in bitshift of NeoPixel example project
8694257 
Fixed bit shift in demo application of using RMT peripheral. Init data array to be transmitted was off by one, as for the first iteration (i==0) the mask was 1<<8, which results in shifted RGB value in color variable
Closes espressif#2921
@david-cermak david-cermak mentioned this issue Jul 14, 2019
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@david-cermak
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Hi @tedhenry100

sorry for such a late response.
Yes, there's an off by one error, thanks for noting! Posted a PR

me-no-dev pushed a commit that referenced this issue Jul 16, 2019
@david-cermak @me-no-dev
RMT: Fix in bitshift of NeoPixel example project (#2986)
1c7e329 
Fixed bit shift in demo application of using RMT peripheral. Init data array to be transmitted was off by one, as for the first iteration (i==0) the mask was 1<<8, which results in shifted RGB value in color variable
Closes #2921
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RMT: Fix in bitshift of NeoPixel example project david-cermak/arduino-esp32
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@tedhenry100 @david-cermak