nrf9160 uart Pull-Up and power consumption

[MosheSmartAmr]

hi all,

i'm trying to disable uart for lower power consumption, i've disables it with:

NRF_UARTE1->TASKS_STOPTX = 1;
NRF_UARTE1->TASKS_STOPRX = 1;

but when i measure the voltage on the rx pin i see 1.8V  (this seems to consume current on the device on the other side of the uart interface - which is turned off )
i assume its in pulled up state, so i'm trying to change it's state to no-pull:

nrf_uarte_txrx_pins_disconnect(NRF_UARTE0);
gpio_pin_configure(uart_wifi, 18, GPIO_PUD_PULL_DOWN);
gpio_pin_configure(uart_wifi, 19, GPIO_PUD_PULL_DOWN);
gpio_pin_write(uart_wifi, 18,0);
gpio_pin_write(uart_wifi, 19,0);

 but it doesnt seem to have any effect.

how can i set this pin to 0, and back to 1 when I need it , on runtime?

Thanks

Moshe

[Vidar Berg]

Hi Moshe, 

Is the external IC power gated? It should drive the RX line to 'high' when it's inactive and powered. So that may explain why you see the current draw when you set the output to 0. 

Also, from your code snippets, it appears that you are stopping UART instance 1 while nrf_uarte_txrx_pins_disconnect() call takes instance 0 as an argument. Not sure if this is intended or not.

Best regards,

Vidar

[MosheSmartAmr]

Hi Vidar,

Thanks for your answer, 

1. I called `nrf_uarte_txrx_pins_disconnect()` on both UARTs (didnt copy it into the snippet).

2. I test this while the external IC is powered off  (it is gated ) . 

3. Just to be clear, even when I  disable UART from the SW, I still measure 1.8v on the TX pin . I guess it is still pulled up . 

Thanks and BR

[Håkon Alseth]

Hi,

 

When the UART is disabled, the RXD is left as an input, and TXD is left as an output (with high level).

This is the routine that I have tested your scenario with:

#include <zephyr.h>
#include <misc/printk.h>
#include <uart.h>

#define TXD_PIN 19

static u8_t uart_buf[1024];

void uart_cb(struct device *x)
{
	uart_irq_update(x);
	int data_length = 0;

	if (uart_irq_rx_ready(x)) {
		data_length = uart_fifo_read(x, uart_buf, sizeof(uart_buf));
		uart_buf[data_length] = 0;
	}
	printk("%s", uart_buf);
}

void main(void)
{
	struct device *uart = device_get_binding("UART_1");

	uart_irq_callback_set(uart, uart_cb);
	uart_irq_rx_enable(uart);
	printk("UART loopback start!\n");
	while (1) {
		static u32_t wakeup_cnt;		
		k_cpu_idle();
		wakeup_cnt++;
		if (wakeup_cnt > 40) {
			wakeup_cnt = 0;
			NRF_UARTE1->TASKS_STOPRX=1;
			while(NRF_UARTE1->EVENTS_RXTO == 0);
			NRF_UARTE1->EVENTS_RXTO = 0;

			NRF_UARTE1->TASKS_STOPTX = 1;
			while(NRF_UARTE1->EVENTS_TXSTOPPED == 0);
			NRF_UARTE1->EVENTS_TXSTOPPED = 0;
			
			NRF_UARTE1->ENABLE = 0;
			NRF_UARTE1->PSEL.TXD = 0xFFFFFFFF;
			NRF_P0_NS->OUTCLR = (1 << TXD_PIN);
		}
	}
}

 

This code assumes that I loopback UART0:TXD to UART1:RXD, and when it has gotten 40 chars, it disconnects the UART1 interface completely.

If I do not clear the GPIO, it is held high. When I run NRF_P0_NS->OUTCLR = 1<<19;, the pin goes low again after disconnecting it from the UARTE1 peripheral.

Could you try this and see if that works at your end?

 

Kind regards,

Håkon

[MosheSmartAmr]

Thanks !! it worked !!

[MosheSmartAmr]

Hi,

Could this be in any way interfering with low power (PSM) mode ? 

although the pin is now down,  the current draw is 2.5ma. 

[MosheSmartAmr]

Hi, 

just to be clearer:

1. the pin is actually pulled down right now.

2. working in power optimmization mode (PSM), Nordic now consumes 2.5ma  (not on Vio).

3. before applying what suggested here, nordic consumed 70ua on power optimization mode.

[Håkon Alseth]

Hi,

 

This should not affect the PSM mode, but it might affect the application in terms of sleep routines.

Is there anything specific that happens when you have disabled the UART? Are you able to see if the nRF9160 is awoken from sleep by anything unpredictable?

 

Kind regards,

Håkon

[MosheSmartAmr]

I don't see any reason that the NRF91 will be awaken once I disable uart. 

could the uart module do that internally? is there a way to disable the uart's module ability to interrupt the NRF91 from sleep ?

[Håkon Alseth]

You can clear the events that are set (EVENTS_*), disable the interrupts (Write 0xFFFFFFFF to NRF_UARTEx->INTENCLR), and see if this has any effect.

[MosheSmartAmr]

unfortunately that did not work. 

still getting the same consumption

[Håkon Alseth]

If the current consumption does not come from VDD_IO, then it should not be related to the IO settings at all, but more in the program flow.

Is there any functions running after disabling the uart which tries to use it again? So that the firmware goes into a bad state, causing the high current consumption?

 

If you're unsure if this comes from VDD_IO, could you try setting it to a input instead of output?

// Input, connected, with pull-down
NRF_P0_NS->PIN_CNF[pin_used] = 0x4;

 

Kind regards,

Håkon

[MosheSmartAmr]

Thanks  Hakon,

Your last answer seemed to direct me to the answer, 

there was an issue with the SW flow,

which leaves the question, is there a way to get an event / interrupt when leaving sleep mode (so I can re-enable uart) ? 

Kind Regards ,

Moshe