TDM/I2S (Time Division Multiplexing/Inter-IC Sound)

General Description

Note

IP Supported: TDM Configures audio TDM/I2S.

The functions and other declarations used in this driver are in cy_tdm.h. You can include cy_pdl.h (ModusToolbox only) to get access to all functions and declarations in the PDL.

Features:

• Supports I2S mode and TDM mode.
• Master and slave functionality.
• Full-duplex transmitter and receiver operation.
• Support for up to 32 channels.
• Programmable channel size (up to 32 bits)
• Programmable channel delay of 0 or 1 bit.
• Delayed sampling support.
• Programmable PCM sample formatting (8, 10, 12, 14, 16, 18, 20, 24, 32 bits).
• Programmable synchronization pulse type.
• Left-aligned and right-aligned sample formatting.
• 128 entry TX FIFO with interrupt and trigger support.
• 128 entry RX FIFO with interrupt and trigger support.

Configuration Considerations

To set up a TDM driver, initialize the TDM Transmitter module in accordance with a configuration structure.

• Each TDM/I2S (TX, RX) pair consists of a TDM/I2S transmitter and a TDM/I2S receiver.
• The transmitter and receiver can function simultaneously and have dedicated clock control.
• The transmitter and receiver have dedicated MMIO registers and a dedicated FIFO.
• The transmitter and receiver have a dedicated FIFO interrupt and FIFO trigger.
• The transmitter trigger is activated when a programmable number of PCM data slots is available in the TX FIFO.
• The receiver trigger is activated when a programmable number of PCM data words is received into the RX FIFO.

To set up TDM, provide the configuration parameters in the cy_stc_tdm_config_t structure.

For example, for Tx configuration, set txEnabled to true, configure txDmaTrigger (depending on whether DMA is going to be used or not), set extClk (if an external clock is used), provide clkDiv, masterMode, sckPolarity, fsyncPolarity, channelSize, wordSize, either i2sMode or TDM (based on Mode setting), fifoTriggerLevel (when the Trig interrupt will be used) and format A similar setup is for the Rx configuration.

To initialize the TDM block, call the Cy_AudioTDM_Init function, providing the filled cy_stc_tdm_config_t structure. Before starting the transmission, enable the Tx Cy_AudioTDM_EnableTx, then fill the first Tx data frame by calling Cy_AudioTDM_WriteTxData. Then call the Cy_AudioTDM_ActivateTx. For the reception the sequence is the same except for filling the first data frame.

For example:

    /* Scenario: Setup a duplex 16-bit TDM interface */
 
    cy_stc_tdm_config_tx_t tdm_lpbk_tx_config =
    {
        .enable = true,
        .masterMode = CY_TDM_DEVICE_MASTER,
        .wordSize = CY_TDM_SIZE_16,
        .format = CY_TDM_LEFT,
        .clkDiv = 16,
        .clkSel = CY_TDM_SEL_SRSS_CLK0,
        .sckPolarity = CY_TDM_CLK,
        .fsyncPolarity = CY_TDM_SIGN,
        .fsyncFormat = CY_TDM_CH_PERIOD,
        .channelNum = 2,
        .channelSize = 16,
        .fifoTriggerLevel = 36,
        .chEn = 0x3,
        .signalInput = 0,
        .i2sMode = true,
    };
    cy_stc_tdm_config_rx_t tdm_lpbk_rx_config =
    {
        .enable = true,
        .masterMode = CY_TDM_DEVICE_SLAVE,
        .wordSize = CY_TDM_SIZE_16,
        .signExtend = CY_ZERO_EXTEND,
        .format = CY_TDM_LEFT,
        .clkDiv = 16,
        .clkSel = CY_TDM_SEL_SRSS_CLK0,
        .sckPolarity = CY_TDM_CLK,
        .fsyncPolarity = CY_TDM_SIGN,
        .lateSample = false,
        .fsyncFormat = CY_TDM_CH_PERIOD,
        .channelNum = 2,
        .channelSize = 16,
        .fifoTriggerLevel = 32,
        .chEn = 0x3,
        .signalInput = 0,
        .i2sMode = true,
    };
    const cy_stc_tdm_config_t tdm_lpbk_config =
    {
        .tx_config = &tdm_lpbk_tx_config,
        .rx_config = &tdm_lpbk_rx_config,
    };
 
    if(CY_TDM_SUCCESS != Cy_AudioTDM_Init(TDM_STRUCT0, &tdm_lpbk_config))
    {
        /* Insert error handling */
    }
 
    /* Clear possible pending interrupts */
    Cy_AudioTDM_ClearTxInterrupt(TDM_STRUCT0_TX, CY_TDM_INTR_TX_MASK);
    Cy_AudioTDM_ClearRxInterrupt(TDM_STRUCT0_RX, CY_TDM_INTR_RX_MASK);
    /* Enable interrupts */
    Cy_AudioTDM_SetTxInterruptMask(TDM_STRUCT0_TX, CY_TDM_INTR_TX_MASK);
    Cy_AudioTDM_SetRxInterruptMask(TDM_STRUCT0_RX, CY_TDM_INTR_RX_MASK);
    /* Enable the TDM interface */
    Cy_AudioTDM_EnableRx(TDM_STRUCT0_RX);
    Cy_AudioTDM_EnableTx(TDM_STRUCT0_TX);

If you use a DMA, the DMA channel should be previously configured. The TDM interrupts (if applicable) can be enabled by calling Cy_AudioTDM_SetTxInterruptMask.

For example, if the trigger interrupt is used during operation, the ISR should call the Cy_AudioTDM_WriteTxData as many times as required for your FIFO payload, but not more than the FIFO size. Then call Cy_AudioTDM_ClearTxInterrupt with appropriate parameters.

If a DMA is used and the DMA channel is properly configured - no CPU activity (or any application code) is needed for I2S/TDM operation.

The I2S frame appears as:

This is an example for the channel length = 32. A similar case exists for the rest channel length configuration, with one limitation: the word length should be less than or equal to the channel length. See the datasheet of your device for more details.

MISRA-C Compliance

The TDM driver has the following specific deviations:

MISRA Rule	Rule Class (Required/Advisory)	Rule Description	Description of Deviation(s)
10.3	R	A composite expression of the "essentially unsigned" type is being cast to a different type category.	The value got from the bitfield physically cannot exceed the enumeration that describes this bitfield. So, the code is safe by design.
11.4	A	A cast should not be performed between a pointer to object type and a different pointer to object type.
20.3	R	The validity of values passed to library functions shall be checked.	This violation is not caused by code changes, i.e. is not a regression.

API Reference
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	Enumerated Types
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