The MCLK pin for I2S is being incorrectly mapped to the BCLK pin for some reason.

[cory123]

I'm implementing the SGTL5000 driver found on the github Nordic playground with the NRF52832. My custom board connects the NRF chip to SGTL5000. I've changed the drv_sgtl5000.h to match my boards layout:

/* I2S pin mapping */
#define DRV_SGTL5000_I2S_PIN_MCLK       21  /* 23 for nRF52832 DK, 1,13 for 52840 */
#define DRV_SGTL5000_I2S_PIN_BCLK       19   /* 20 for nRF52832 DK, 1,11 for 52840 */
#define DRV_SGTL5000_I2S_PIN_LRCLK      20  /* 22 for nRF52832 DK, 1,12 for 52840 */
#define DRV_SGTL5000_I2S_PIN_RX         18  /* 25 for nRF52832 DK, 1,15 for 52840 */
#define DRV_SGTL5000_I2S_PIN_TX         17  /* 24 for nRF52832 DK, 1,14 for 52840 */

I used the nReset pin for MCLK pin for no specific reason. When the driver tries to communicate via I2C with the SGTL it gets no ACK of address. After closer inspection, I've found that the MCLK pin is not getting clocked which is necessary for I2C to work. I measured the MCLK pin 21 with my multi-meter, and got 0 Hz. When measuring the frequency of the BCLK pin 19 I see 4 Mhz. It looks like MCLK is outputing on the BCLK pin for some reason. I've traced the pin configurating in the the sgtl driver code. The MCLK pin is definitely set to 21 all the way through to the I2S registers.

This issue may be related to https://devzone.nordicsemi.com/f/nordic-q-a/24609/i2s-with-reset-pin

Any advice on this issue would be greatly appreciated!

[cory123]

On second look, the LRCLK and BCLK pins are being correctly output. The only problem is the MCLK pin 21 is not output.

In the post I mentioned above, there is a mention of UICR which must be configured. How can I configure the UICR so that pin 21 is not used for reset? I've read something about changing the bootloader to set UICR to a different value. Should I try this?

[cory123]

One more note. I've identified the flag CONFIG_GPIO_AS_PINRESET which enables pin reset. In my SES project options I have confirmed that this flag is not defined under the preprocessor section for both Debug and Release. The CONFIG_GPIO_AS_PINRESET  section in system_nrf52.c (below) in SES  is grayed out confirming that CONFIG_GPIO_AS_PINRESET is not defined. So I still don't know my pin 21 is not acting like a GPIO.

/* Configure GPIO pads as pPin Reset pin if Pin Reset capabilities desired. If CONFIG_GPIO_AS_PINRESET is not
      defined, pin reset will not be available. One GPIO (see Product Specification to see which one) will then be
      reserved for PinReset and not available as normal GPIO. */
    #if defined (CONFIG_GPIO_AS_PINRESET)
        if (((NRF_UICR->PSELRESET[0] & UICR_PSELRESET_CONNECT_Msk) != (UICR_PSELRESET_CONNECT_Connected << UICR_PSELRESET_CONNECT_Pos)) ||
            ((NRF_UICR->PSELRESET[1] & UICR_PSELRESET_CONNECT_Msk) != (UICR_PSELRESET_CONNECT_Connected << UICR_PSELRESET_CONNECT_Pos))){
            NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Wen << NVMC_CONFIG_WEN_Pos;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NRF_UICR->PSELRESET[0] = 21;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NRF_UICR->PSELRESET[1] = 21;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NRF_NVMC->CONFIG = NVMC_CONFIG_WEN_Ren << NVMC_CONFIG_WEN_Pos;
            while (NRF_NVMC->READY == NVMC_READY_READY_Busy){}
            NVIC_SystemReset();
        }
    #endif

[Stian Røed Hafskjold]

Hi, removing the CONFIG_GPIO_AS_PINRESET definition in your project does not clear the PSELRESET register in UICR. You will have to manually erase UICR. Please try to do a full chip erase, and the P21 pin should be available as a regular GPIO.

[cory123]

I have tried doing a full erase with nrfjprog -e and P21 is still not working as a GPIO. I read the UICR into a hex file before and after the erase. The UICR contents in both cases were the same, all FF. I've also read the UICR after doing nrfjprog --program my_program.hex. The contents are still all FF.

In the datasheet I've noticed that the reset value for all UICR registers is all FF. Is it possible that something is preventing UICR from being changed from its reset value? If P21 is currently acting as nReset, do I need to pull it high to program UICR or something?

data.hex

[Stian Røed Hafskjold]

After the UICR is changed, the chip has to be power cycled in order for the changes to take effect (i.e. you need a POR (Power on reset)). Did you try that? The reset pin is configured in hardware during boot, before the CPU has started running any code.

If you read 0xFFFFFFFF from both PSELRESET registers after a power cycle and after the code has started running, the pin reset is definitely not enabled, and it should be possible to use the pin as a regular GPIO.

Did you try using another pin for MCLK? Also, have you tried not using P21 for the I2S, but just set it as a regular GPIO output, and see if you are able to set it high and/or low?

[cory123]

I just tried your advice. When I assign MCLK to another pin, MCLK is output as expected.

When I configure P21 as output (see below) and set it high I get 3.3 V as expected, but when I set it low I still get 3.3 V. Is there some internal pull-up that is preventing the output going low?

 nrf_gpio_cfg_output(21);
 nrf_gpio_pin_clear(21);