Bus fault from spi_write_dt

Question

I'm getting a bus fault from the following code when it hits spi_write_dt:

    printk("Getting spi0\n");
	spi_dev = DEVICE_DT_GET(DT_NODELABEL(spi0));

    if( spi_dev == NULL ) {
        printk("SPI not initialized.\n");
        return SPI_NOT_INITIALIZED;
    } else if( ! device_is_ready(spi_dev) ) {
        printk("SPI not ready.\n");
        return SPI_NOT_READY;
    }
    uint8_t spi_bytes[2] = {0};
    struct spi_buf my_spi_buf[1]; // Buffer to hold one set of SPI data
    my_spi_buf[0].buf = spi_bytes; // The byte array to send
    my_spi_buf[0].len = 2; // Number of bytes in buffer
    struct spi_buf_set tx_buff;
    tx_buff.buffers = my_spi_buf;
    tx_buff.count = 1;

    return spi_write_dt(spi_dev,&tx_buff);

Here's the fault as reported to the UART:

Getting spi0
[00:00:23.264,434] <err> os: bus_fault: ***** BUS FAULT *****
[00:00:23.264,434] <err> os: bus_fault:   Precise data bus error
[00:00:23.264,465] <err> os: bus_fault:   BFAR Address: 0x30303033
[00:00:23.264,465] <err> os: esf_dump: r0/a1:  0x000328ea  r1/a2:  0x0002e00c  r2/a3:  0x30303033
[00:00:23.264,495] <err> os: esf_dump: r3/a4:  0x00000000 r12/ip:  0x0000000c r14/lr:  0x00011a9f
[00:00:23.264,495] <err> os: esf_dump:  xpsr:  0x01000000
[00:00:23.264,526] <err> os: esf_dump: Faulting instruction address (r15/pc): 0x00011ac8
[00:00:23.264,556] <err> os: z_fatal_error: >>> ZEPHYR FATAL ERROR 0: CPU exception on CPU 0
[00:00:23.264,587] <err> os: z_fatal_error: Current thread: 0x20002088 (unknown)
[00:00:23.368,530] <err> fatal_error: k_sys_fatal_error_handler: Resetting system
*** Booting Zephyr OS build v3.2.99-ncs2 ***
etc...

My overlay file sets the status to okay and sets a GPIO as a chip select:

&spi0 {
    cs-gpios = <&gpio0 18 GPIO_ACTIVE_LOW>;
    status = "okay";
};

My module is the Laird BL652 which gives me a dts file with this in it:

&spi0 {
	compatible = "nordic,nrf-spi";
	/* Cannot be used together with i2c0. */
	/* status = "okay"; */
	cs-gpios = <&gpio0 22 GPIO_ACTIVE_LOW>;
	pinctrl-0 = <&spi0_default>;
	pinctrl-1 = <&spi0_sleep>;
	pinctrl-names = "default", "sleep";
};

My dev environment version is 2.30.

Any idea why I might be getting the bus fault?

Bret Foreman · Accepted Answer

I think I found my problem. Here's the prototype for spi_write_dt: 
 static inline int spi_write_dt(const struct spi_dt_spec *spec,
 const struct spi_buf_set *tx_bufs) 
 Note that it takes a pointer to a spi_dt_spec structure, not a device. Inside that struct are a pointer to a device and also a spi_config struct which apparently is only used when the device is a SPI slave. 
 Another wrinkle is that the argument to spi_write_dt has to be of type const, which makes it hard to initialize the .bus field in the spi_dt_spec struct. Here's a trick to do it at declaration time: 
 const struct spi_buf my_spi_buf[1] = {// Buffer to hold one set of SPI data
 [0].buf = spi_bytes,// The byte array to send
 [0].len = 2// Number of bytes in buffer
 };
 const struct spi_buf_set tx_buff = {
 .buffers = my_spi_buf,
 .count = 1
 };

Bus fault from spi_write_dt

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