TWI Current Consumption

RE: TWI Current Consumption

Kenneth — Tue, 24 Mar 2020 14:25:58 GMT

So I assume you have a twi_handler() that will set m_xfer_done. And I assume you clear m_xfer_done before calling nrf_drv_twi_tx() or nrf_drv_twi_rx(). By doing this you can have a while loop after nrf_drv_twi_tx() and nrf_drv_twi_rx() that wait for m_xfer_done is set.

I assume you are calling all nrf_drv_twi* calls from main or an interrupt context that is lower priority than the twi interrupt, else the twi_handler() will not be able to execute.

If the TWI transfers are slower than you expect, then you should check out the actual TWI transfer using a logic analyzer (monitor the SCL and SDA pins). Have in mind though that even if the sensor is fast to sample, the serial interface is still limited to the clock speed of TWI, which may be <400kHz or lower. So 10ms may not be far off expected depending on the number of bytes and possible wait states.

Best regards,
Kenneth

RE: TWI Current Consumption

Nadeem — Tue, 24 Mar 2020 11:07:25 GMT

Hey Kenneth ,

Thanks for your reply.. Can you help me on how to send consecutive reads and writes.. I believe your right in the fact that its because of the CPU running and not being able to sleep.

The issue is if i remove the Delays i always get NRF_busy error. although i have while (m_xfer_done == false);

I tried to make a function called waitms() with a single shot timer, but the timer handler is not being called. It works fine when i dont send any TWI reads or writes.. but when i send some read and writes the handler is not called..

My idea was :-

void writeRegister(uint8_t RegisterAddr, uint8_t Data)
{
ret_code_t err_code;
//while (m_xfer_done == false);
uint8_t reg[2] = {RegisterAddr,Data};
err_code = nrf_drv_twi_tx(&m_twi, MP121_ADDR, reg, 2, false);
APP_ERROR_CHECK(err_code);
while (m_xfer_done == false);
watMs(10);

while (WaitFlage== false);
}

But this doesnt work as the Waitflag is not being set by the single shot timer handler. Maybe my idea is not feasible in first place.. if not can you advise how to avoid wasted cpu cycles and put the cpu in sleep mode..

Secondly is the NRF_busy related to the Sensor chip or something else? I initialy thought the sensor needed time to process the request but when i saw the data sheet of the mpr121 it is pretty fast .. only needs 1.5 us to respond , while i am needing atleast 10 ms. to avoid getting the nrf busy error.

RE: TWI Current Consumption

Kenneth — Mon, 23 Mar 2020 09:38:50 GMT

You may get some pointers here in general:
https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/optimizing-power-on-nrf52-designs

If the CPU is running (not in sleep) it will draw a few mA, in sleep the chip should draw only a few uA. If it is drawing tens of uA you should check for floating GPIO's or if it may be due to a known errata that require workaround:
https://infocenter.nordicsemi.com/topic/errata_nRF52832_Rev2/ERR/nRF52832/Rev2/latest/err_832_new.html

Best regards,
Kenneth

RE: TWI Current Consumption

Nadeem — Thu, 19 Mar 2020 16:43:05 GMT

I have a handlre whicb just stores the return data to a global variable. What concerns me is two things.. that how is it possible when running the twi can consume so much data.. also when sd power of.. my system still consumes 60 ua...

I am already using power manage run as shown in idle state handle function...

RE: TWI Current Consumption

Kenneth — Thu, 19 Mar 2020 15:17:54 GMT

I notice you are writing: nrf_drv_twi_init(&m_twi, &twi_lm75b_config, twi_handler, NULL);

But I can't see your twi_handler()?

Have you tried:

nrf_drv_twi_init(&m_twi, &twi_lm75b_config, NULL, NULL);

If you don't have any debugging, you can use nrf_pwr_mgmt_run() directly. What is the implementation of nrf_pwr_mgmt_run()?

RE: TWI Current Consumption

Nadeem — Thu, 19 Mar 2020 11:27:40 GMT

Read and write functions:

void writeRegister(uint8_t RegisterAddr, uint8_t Data)
{
ret_code_t err_code;
uint8_t reg[2] = {RegisterAddr,Data};
err_code = nrf_drv_twi_tx(&m_twi, MP121_ADDR, reg, 2, false);
APP_ERROR_CHECK(err_code);
while (m_xfer_done == false);
nrf_delay_ms(10);
}

void readRegister8(uint8_t RegisterAddr)
{
ret_code_t err_code;
uint8_t reg[2];
reg[0] =RegisterAddr;
nrf_delay_ms(20);
err_code = nrf_drv_twi_tx(&m_twi, MP121_ADDR, reg, 1, true);
nrf_delay_ms(100);
if (NRF_SUCCESS == err_code)
err_code = nrf_drv_twi_rx(&m_twi, MP121_ADDR, &m_sample, 1);
APP_ERROR_CHECK(err_code);
nrf_delay_ms(100);
}
void readRegister16(uint8_t RegisterAddr)
{
ret_code_t err_code;
uint8_t reg[2];
reg[0] =RegisterAddr;
nrf_delay_ms(100);
err_code = nrf_drv_twi_tx(&m_twi, MP121_ADDR, reg, 1, true);
nrf_delay_ms(100);
if (NRF_SUCCESS == err_code)
err_code = nrf_drv_twi_rx(&m_twi, MP121_ADDR, &m_sample, 2);
APP_ERROR_CHECK(err_code);
nrf_delay_ms(100);
}