4-TX Line Audio Playback via SAI1 on MIMXRT1170 and CS42448 1. Introduction This document focuses on utilizing the MIMXRT1170-EVKB development board and the CS42448 audio expansion board to achieve specific audio playback functionality through four TX data lines of the SAI1 module. With its real-time performance and high integration, the i.MX RT1170 is widely used in automotive, industrial, and IoT fields. The Arm Cortex-M7 core runs at up to 1GHz, features 2MB on-chip RAM, and offers various memory and connectivity interfaces. It supports multiple audio interfaces, including SAI-1, SAI-2, SAI-3, SAI-4, PDM, ASRC, SPDIF, and MQS. This document details the implementation of 8-channel audio output using the RT1170 EVKB development board and CS42448 Audio Card via four TX data lines of the SAI1 module. It also explains how to generate 8-channel audio data compatible with SDK example requirements. The CS42448 Audio Card can be directly connected to the RT1170 EVKB board, enabling developers to build more complex audio applications. The NXP SDK provides the example 'evkbmimxrt1170_sai_edma_multi_channel_transfer_cm7,' which by default enables two transmission channels (TX_DATA0 and TX_DATA1). When running, 1kHz sine wave audio signals can be heard from the J6 and J7 interfaces of the CS42448 Audio Card. However, when customer requirements demand four TX data lines (TX_DATA0 to TX_DATA3), each transmitting different audio, how can this be achieved? This document explores and validates this scenario in depth. 2. SAI Overview (1) RT1170 Chip SAI Module Features According to the IMXRT1170RM datasheet, SAI2, SAI3, and SAI4 modules each have only one data line for input/output, while SAI1 has four, making it the only module supporting multi-line communication. (2) Configuration Highlights To implement the four TX data line solution, it is crucial to configure the Transmit Configuration 3 (TCR3) TCE register correctly. According to IMXRT1170RM Table 54-2, Option0 should be selected for pin configuration. To enable TX_DATA0 to TX_DATA3, set bits 16–19 of the SAI1 TCR3 register to '1111'. Similarly, for multiple Rx data lines, configure bits 16–19 of the SAI1 RCR3 register (RCE).   3. Hardware Preparation (1) Required Hardware - Mini/micro USB cable - MIMXRT1170-EVKB development board - Personal computer - Headphones (OMTP standard) - CS42448 Audio Card (2) Hardware Modifications on MIMXRT1170-EVKB Solder Resistors: R2008, R2022, R2011, R2021, R2009, R2010, R2012, R2016, R1998, R2013, R2014, R2018, R2017, R2000 Remove Resistors: R2001, R2002, R2003, R2004, R2005, R2006, R2007 After completing the hardware modifications, connect the CS42448 Audio Card to the J76 interface of the MIMXRT1170-EVKB board. 4. Audio Source Preparation The free and powerful audio editing software Audacity is used to convert MP3 files to .wav format. Since each TX data line transmits two audio channels, a total of 8 channels are needed. (1) Audio Channel Allocation Strategy Using Audacity, multiple audio channels were generated. 'HelloWorld' is mono and reused. Allocation is as follows: - TX_DATA0: HelloWorld → Channel 1 & Channel 5 - TX_DATA1: Audio1 → Left: Channel 2, Right: Channel 6 - TX_DATA2: Audio2 → Left: Channel 3, Right: Channel 7 - TX_DATA3: Audio3 → Left: Channel 4, Right: Channel 8 On the CS42448 Audio Card: - J6 plays TX_DATA0 (HelloWorld) - J7 plays  TX_DATA1(Audio1) - J8 plays TX_DATA2(Audio2) - J9 plays TX_DATA3(Audio3) (2) Audio Format Requirements The converted .wav files must match the format used in the NXP SDK example: 48kHz sampling rate and 16-bit width. Ensure these parameters are correctly set in Audacity during conversion. (3) Audio Data Processing To convert the generated HelloWorld-8-channel.wav file into a C language array using WinHex, you need to remove the first 44 bytes, which constitute the standard WAV file header. This step is crucial because the SDK example utilizes raw audio data. For those interested, examining the structure of a WAV file can provide deeper insight into this process. Alternatively, this conversion from WAV format to a C array can also be accomplished using other tools or methods. 5. Software Modifications (1) Configure SAI1 Module Registers To enable four TX data lines, set the TCE bits in the SAI1 TCR3 register. In the NXP SDK code, modify the macro DEMO_SAI_CHANNEL_MASK and configure saiConfig in I2S mode. The function SAI_TransferSendEDMA will set the TCR3 TCE register accordingly. (2) Replace Audio Data and Modify Macros Replace the uint8_t music[] array in the SDK example’s music.h file with the C array generated earlier. Also, update the macro MUSIC_LEN to match the byte length of the new array, ensuring it is a multiple of 1600. After completing all steps, compile and flash the program to the MIMXRT1170-EVKB board. Connect headphones to the CS42448 Audio Card’s J6,J7,J8,J9 interfaces to hear the respective audio outputs.   6. Conclusion This project successfully implements the transmission of four TX data lines via the SAI1 module using the CS42448 Audio Card and MIMXRT1170-EVKB development board. Experimental validation confirms support for multi-channel independent audio output. Each TX data line can output distinct audio content through the CS42448’s physical interfaces (J6–J9), meeting the needs of complex audio scenarios.