[I2S] removes code forcing two slots in PCM Short Slot (IDFGH-14064)

[gl-agnx]

Description

Changes the i2s_hal and i2s_tdm configuration to not force two slots when only one slot is required.

This issue prevents a configuration of I2S_STD_SLOT_LEFT and I2S_SLOT_MODE_MONO.

If two slots are required, then I2S_STD_SLOT_BOTH could be specified by the use

This change was made because it was not possible to generate a 16-bit PCM output that's mono with only one slot, which is the case in some configurations

Explanation:
I2S_SLOT_MODE_MONO forces data to repeat across all slots. By definition, I2S_STD_SLOT_LEFT, I2S_STD_SLOT_RIGHT, or I2S_STD_SLOT_BOTH define whether we enable the left, right or both slots with 1 bit encoding.
However, requiring always at least 2 slots removes the ability to send out a single slot and makes I2S_STD_SLOT_BOTH useless.

The current code was enforcing the requirement of 2 slots at a low level for some reason in mono.

Related

None

Testing

Tested on ESP32-S3-DevKitC with a logic analyzer and can see properly that only a single slot is sent when configuring I2S_STD_SLOT_LEFT. Tested with I2S_STD_SLOT_BOTH and can see that both slots are being sent, as was the case before this cahnge.

Configuration example:

i2s_tdm_config_t tdm_cfg = {
        .clk_cfg  = I2S_TDM_CLK_DEFAULT_CONFIG(8000),
       
        .slot_cfg = I2S_TDM_PCM_SHORT_SLOT_DEFAULT_CONFIG(config->data_width, I2S_SLOT_MODE_MONO, I2S_STD_SLOT_LEFT),
        .gpio_cfg = {
            .mclk = config->mclk_pin,    // some codecs may require mclk signal, this example doesn't need it
            .bclk = config->bclk_pin,
            .ws   = config->ws_pin,
            .dout = config->dout_pin,
            .din  = config->din_pin, // In duplex mode, bind output and input to a same gpio can loopback internally
            .invert_flags = {
                .mclk_inv = config->mclk_pin_inv,
                .bclk_inv = config->bclk_pin_inv,
                .ws_inv   = config->ws_pin_inv,
            },
        },
    };

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[L-KAYA]

Thanks for looking into this issue! And you've caught the exact buggy line.

But removing the limitation directly will affect the Philips and MSB format, and might cause some breaking changes, so I suggest to add one more conditions so that we can only allow one slot in PCM SHORT format. (See suggestions as follows)

[L-KAYA]

handle->total_slot = (handle->total_slot < 2) && (slot_cfg->ws_width != 1) ? 2 : handle->total_slot;

[atanisoft]

Similar here with adding () around the conditions.

[L-KAYA]

cnt = (cnt < 2) && (slot_cfg->tdm.ws_width != 1) ? 2 : cnt;

[atanisoft]

I'd suggest:

cnt = ((cnt < 2) && (slot_cfg->tdm.ws_width != 1)) ? 2 : cnt;

as depending on the compiler optimization it may end up assigning zero to cnt if the first piece (cnt < 2) is evaluated first and shortcircuits the remaining operation.

[L-KAYA]

Could you help to update the commit?

[suda-morris]

sha=3e0e2b1e75934d74c7b30574e57033ffc99a672e