wrong array size in iis3dwb fifo example

[chenjy96]

Device part numbers

IIS3DWB nRF52840

Type of bug

I wrote my program with reference to iis3dwb fifo example, but the spi transfer will be stuck at the second loop.

Describe the bug

I check the value of num which is assigned on here. In the first loop, the value of num is equal to FIFO_WATERMARK, but after the second loop, the value is always 511 which is the same value of FIFO size. So the size of array fifo_data which is defined here, should be 511, rather than FIFO_WATERMARK.

[mu578]

511 is the max value that could be assigned, so in the example the window data is set to 256 then the cursor should move on thru the FIFO queue buffer. so that's not a size problem in itself but a mismatch logic between raw memory and processed frames.

[chenjy96]

511 is the max value that could be assigned, so in the example the window data is set to 256 then the cursor should move on thru the FIFO queue buffer. so that's not a size problem in itself but a mismatch logic between raw memory and processed frames.

I modified iis3dwb fifo example by using nRF SDK, but the value of num which represent number of unread data is not as I expected. In this example, value of num should be the same as FIFO_WATERMARK when FIFO_ WTM_IA at FIFO_STATUS2 register is 1. But my situation is that the value of num is always 512 after the second loop. Can you tell me the probable reason? I'm concerned that FIFO_WTM_IA is not being triggered properly, maybe resulting in getting data that will be missing.

By the way, my read_reg and write_reg implementation is showed below.

uint8_t SpiInOut (stmdev_ctx_t* spi_ctx, uint8_t outData)
{
    uint32_t err_code;
    uint8_t inData ;

    if ((spi_ctx == NULL) || (&(spi_ctx->spi_handle) == NULL))
    {
        APP_ERROR_CHECK_BOOL (false);
    }

    err_code = nrf_drv_spi_transfer (&(spi_ctx->spi_handle), &outData, 1, &inData, 1);
    APP_ERROR_CHECK(err_code);

    return inData;
}

int32_t SpiWriteRegisters(void* handle, uint8_t reg, const uint8_t* buffer, uint16_t len)
{
    UNUSED_PARAMETER(handle);

    GpioWrite(&iis3dwb_.spi.Nss, 0);
    SpiInOut(&iis3dwb_.spi, reg);
    for(uint16_t i = 0; i < len; i++)
    {
        SpiInOut(&iis3dwb_.spi, buffer[i]);
    }
    GpioWrite(&iis3dwb_.spi.Nss, 1);

    return 0;
}

int32_t SpiReadRegisters(void* handle, uint8_t reg, uint8_t* buffer, uint16_t len)
{
    UNUSED_PARAMETER(handle);

    // Set first bit to 1;
    reg |= 0x80;
    GpioWrite(&iis3dwb_.spi.Nss, 0);
    SpiInOut(&iis3dwb_.spi, reg);

    for(uint16_t i = 0; i < len; i++)
    {
        buffer[i] = SpiInOut(&iis3dwb_.spi, 0);
    }

    GpioWrite(&iis3dwb_.spi.Nss, 1);

    return 0;
}

[mu578]

Hello I didn't have a chance to look into was just casting an educated guess (top of my head) on managing a circular stream ; Do you have any compilation warnings or so ? something not initialized ? is FIFO_WATERMARK re-defined somewhere?