I2S wrong bclk for internal DAC (IDFGH-6697)

[s-hadinger]

Environment

• Development Kit: [M5StickC]
• Module or chip used: [ESP32-PICO-D4]
• IDF version [4.4]
• Build System: [Pio]
• Compiler version toolchain-xtensa-esp32 8.4.0+2021r2-patch2
• Operating System: [macOS]
• Using an IDE?: [PlatformIO]
• Power Supply: [USB]

Problem Description

When using I2S with internal DAC, 2 channels, 16000 frames/sec, the sound emitted is a short swaks and DMA buffers are emptied far too fast compared to regular I2S audio with external chip.

Problem is largely described in espressif/arduino-esp32#5938

Expected Behavior

The original PCM sound is the following and lasts over 660ms:

Actual Behavior

Recording the output with a scope shows a correct waveform but played 11x faster than normal speed.

I did a detour on i2s_hal_tx_clock_config() to check what clock values were calculated, and force-injected some different clock values until the sound was good again.

With the previous setting: 16KHz, 2 channels, internal DAC. IDF calculates the following clock:
sclk=160000000 mclk=128000 bclk=64000 mclk_div=1250 bclk_div=2

Although the number seem correct, mclk_div hardware is only 8 bits, so 1250 is overflowing.

Injecting my own calculated value, I made it work at correct speed with:
sclk=160000000 mclk=1024000 bclk=32000 mclk_div=156 bclk_div=32

Having a combined mclk_div=156 bclk_div=32 achieves a divider of ~5000 over sclk.

I suppose that an easy patch would be to set bclk_div=32 instead of bclk_div=2 and it should allow for all audio frequencies.

Steps to reproduce

Code to reproduce this issue

Debug Logs

Other items if possible

• sdkconfig file (attach the sdkconfig file from your project folder)
• elf file in the build folder (note this may contain all the code details and symbols of your project.)
• coredump (This provides stacks of tasks.)

[Alvin1Zhang]

Thanks for reporting and sharing the updates, fix is available at 19f4eca, feel free to reopen.