Thingy 91: Bus Fault when trying to set up I2S on Zephyr

Question

Hello,

I am trying to build a Zephyr application for the Thingy91 which uses the I2S module to receive audio data from an external microphone and sends this data via BLE to a connected device.
For the initialization of the I2S module I used the code listed below:

ISR_DIRECT_DECLARE(i2s_isr_handler) {
    nrfx_i2s_irq_handler();
    ISR_DIRECT_PM();
    return 1;
}

static bool init_nrfx_i2s(void) {
    IRQ_DIRECT_CONNECT(I2S_IRQn, 0, i2s_isr_handler, 0);

    nrfx_i2s_config_t i2s_config = {
        .sck_pin        = I2S_BCLK_PIN,
        .lrck_pin       = I2S_LRCLK_PIN,
        .mck_pin        = NRFX_I2S_PIN_NOT_USED,
        .sdout_pin      = NRFX_I2S_PIN_NOT_USED,
        .sdin_pin       = I2S_SDIN_PIN,
        .irq_priority   = NRFX_I2S_CONFIG_IRQ_PRIORITY,
        .mode           = NRF_I2S_MODE_MASTER,
        .format         = NRF_I2S_FORMAT_I2S,
        .alignment      = NRF_I2S_ALIGN_RIGHT,
        .sample_width   = NRF_I2S_SWIDTH_16BIT,
        .channels       = NRF_I2S_CHANNELS_RIGHT,
        .mck_setup      = NRF_I2S_MCK_32MDIV16,
        .ratio          = NRF_I2S_RATIO_128X
    };

    return nrfx_i2s_init(&i2s_config, i2s_event_handler) == NRFX_SUCCESS;
}

However, when the function nrfx_i2s_init is called, Zephyr crashes with the following bus fault:

***** Booting Zephyr OS build v2.0.99-ncs1 *****                                
[00:00:00.085,144] <inf> main: I2S/BLE sample started.                          
[00:00:00.212,677] <inf> flac: FLAC module initialized.                         
[00:00:00.339,416] <err> os: ***** BUS FAULT *****                              
[00:00:00.445,831] <err> os:   Precise data bus error                           
[00:00:00.572,662] <err> os:   BFAR Address: 0x40028504                         
[00:00:00.699,676] <err> os: r0/a1:  0x10000000  r1/a2:  0x00000000  r2/a3:  0x4
[00:00:00.869,812] <err> os: r3/a4:  0x40028000 r12/ip:  0x00000001 r14/lr:  0x0
[00:00:01.039,947] <err> os:  xpsr:  0x21000000                                 
[00:00:01.146,057] <err> os: Faulting instruction address (r15/pc): 0x000166ec  
[00:00:01.295,227] <err> os: >>> ZEPHYR FATAL ERROR 0: CPU exception            
[00:00:01.443,511] <err> os: Current thread: 0x200208e4 (unknown)               
[00:00:01.591,552] <err> os: Halting system

Debugging the function reveals that the application crashes as soon as it is trying to set the I2S mode.

I am using the SDK version 1.1.0 and Zephyr 2.0.99.

Could there be an issue with the device tree configuration? I have not seen an I2S module declaration anywhere.

Kind regards

Nils