Flow control is not working between nrf9160 and nrf5340

[AKO]

I am using 9160 as slave which communicates with nrf5340(master) over UART. with flow control disabled everything works but as soon as I enable the hardware flow control then the nf9160 is not able to send the data to nRF5340.

My configuration:

• at 5340 side:

&uart0 {
status = "okay";
current-speed = <460800>;
pinctrl-0 = <&uart0_default>;
pinctrl-1 = <&uart0_sleep>;
pinctrl-names = "default", "sleep";
hw-flow-control;
};

uart0_default: uart0_default {
group1 {
psels = <NRF_PSEL(UART_RTS, 1, 12)>,
<NRF_PSEL(UART_CTS, 1, 13)>;
};
group2 {
psels = <NRF_PSEL(UART_TX, 0, 3)>,
<NRF_PSEL(UART_RX, 0, 5)>;
bias-pull-up;
};
};

uart0_sleep: uart0_sleep {
group1 {
psels = <NRF_PSEL(UART_TX, 0, 3)>,
<NRF_PSEL(UART_RX, 0, 5)>,
<NRF_PSEL(UART_RTS, 1, 12)>,
<NRF_PSEL(UART_CTS, 1, 13)>;
low-power-enable;
};
};

• AT 9160 side:

&uart1 {
status = "okay";
hw-flow-control;
current-speed = <460800>;
pinctrl-0 = <&uart1_default>;
pinctrl-1 = <&uart1_sleep>;
pinctrl-names = "default", "sleep";
};

uart1_default: uart1_default {
group1 {
psels = <NRF_PSEL(UART_TX, 0, 29)>,
<NRF_PSEL(UART_RTS, 0, 27)>,
<NRF_PSEL(UART_CTS, 0, 26)>,
<NRF_PSEL(UART_RX, 0, 28)>;
};
};

uart1_sleep: uart1_sleep {
group1 {
psels = <NRF_PSEL(UART_TX, 0, 29)>,
<NRF_PSEL(UART_RX, 0, 28)>,
<NRF_PSEL(UART_RTS, 0, 27)>,
<NRF_PSEL(UART_CTS, 0, 26)>;
low-power-enable;
};
};

I have also verified in the peripheral that it says flow control is enabled at both the sides

[Einar Thorsrud]

Hi,

The flow control pins are active low, and I see from the logic analyzer trace that the pins are low most of the time (though it is difficult to see the details as it is zommed out). I also see that there si a bit of data exchanged, but it is difficult to see. Can you elaborate on how this works or not (what are you attempting to send/receive, compared to what you do)? Also, how is the hardware connected? Did you for instance mix up so that RTS and CTS are not crossed?

[AKO]

Yes you are right, from 9160 the first transaction does work but when a large data needs to sent then it does not work(it doesnot reaches to 5340) Also I am getting UART TX ABORTED error

[Einar Thorsrud]

This is odd, so I have quite a few additional questions:

1. Is the only difference flow control or not?
2. Can you show the configuration you use without flow control as well, and plots showing both flow control and no flow control while attempting to send the same data?
3. Perhaps also the code that does UART communication on both ends?
4. Did you do any other changes when things stopped working than enable flow control?
5. Can you verify that the flow control pins are properly connected physically? Physically, which pins did you connect to each other (particuarily the CTS and RTS pins)?

[AKO]

1.) Yes, the only difference is Flow Control.

2.) The only change is:
&uart1 {
status = "okay";
//hw-flow-control;
current-speed = <460800>;
pinctrl-0 = <&uart1_default>;
pinctrl-1 = <&uart1_sleep>;
pinctrl-names = "default", "sleep";
};

4.) No other changes. 

[Einar Thorsrud]

Hi,

I see. This shows you disabling flow control. Can you show how you have connected the pins between the nRF9160 and the nRF5340? And how the pins are configured? I ask becasue I wonder if there is an issue in the connection (RTS and CTS pins crossed, perhaps?)

[AKO]

nrf5340:

Signetik with nrf9160:

Tx code:

bool Tx(uint8_t *txBuff, size_t numBytes)
{
bool ret = false;
if (_LockTx())
{
if (CHECK_IF_OFF(GetCurrentPowerState()))
{
LOG_DBG("tried to tx when UART is off!\n");
_UnlockTx();
return false;
}

if (numBytes <= _txBufferSize)
{
int status = 0;

status = uart_tx(_uartDevice, txBuff, numBytes, (int32_t)(_byteTime_us * numBytes));
if (status == 0)
{
status = k_sem_take(&_txSemaphore, K_USEC(_byteTime_us * numBytes));
if (status == 0)
{
LOG_DBG("successfully transmitted %u bytes\n", numBytes);
ret = true;
}
else
{
LOG_ERR("tx timed out!\n");
}
}
else
{
LOG_ERR("tx failed! code: %d\n", status);
LOG_ERR("device name: %s\n", _uartDevice->name);
}
}
else
{
LOG_ERR("tx failed! num bytes to tx (%u bytes) is larger than the UART buffer size (%u bytes)\n", numBytes, _txBufferSize);
}

_UnlockTx();
}

return ret;
}

The logic analyzer is connected at 5340 side where RTS pin is not toggling

[AKO]

We are using the following:

• Zephyr: 3.6.99
• nRF SDK version: 2.7

[Einar Thorsrud]

Hi,

The flow control signals are active low, so here the CTS is low for most of the time (meaning the other device can send data). Could it be that you have swapped the RTS and CTS lines? Does swapping them help?

That aid, I notice that the CTS pin in this plot is high for every byte, meaning flow control is used for some reason. Could it be that you have set up single byte UART buffers, and that explains it? Can you double check and if so, increase UART buffer sizes?

If that is not it, I would suggest testing on two DKs if you have them and if you can reproduce there as well, I can have a look at the code and tets on my end. If you can only reproduce on your HW, we need to look more closely at that.