power optimal twi tx/rx

[rookie]

Hi - I am wondering what is the power optimal way to read/write with the TWI module. I do a tx and rx with the TWI interface. I have something like this, from the examples to read data from a i2c supported device:

// read from i2c device

uint16_t timeout = 10000;
nrf_drv_twi_tx();

while((!twi_tx_done) && --timeout); // twi_tx_done is in the twi_handler for NRF_DRV_TWI_XFER_TX event
twi_tx_done = false;

timeout = 10000;
nrf_drv_twi_rx();
while((!twi_rx_done) && --timeout); // twi_rx_done is in the twi_handler for NRF_DRV_TWI_XFER_RX event
twi_rx_done = false;

I am not sure if this is the most optimal way of waiting, since it's in a busy loop. Is there a better way to write this?

[awneil]

By "optimal" do you really mean "minimum" - or do you also have other factors to consider ?

Just spinning in a busy loop is never going to be low-power - as it requires the CPU to be running at full speed, without letting it do anything useful.

Could you not let it sleep, and wake on the "finished" event?

[rookie]

Yes, I mean minimal. Not sure what other factors may be involved? In this case it is really about minimizing current draw. 

I agree busy loop is not optimal. How do I let it sleep until I get an event, say a NRF_DRV_TWI_XFER_TX or NRF_DRV_TWI_XFER_RX? Do I use _WFE() ?

[awneil]

rookie said:

Not sure what other factors may be involved?

Common things include:

• You might need some things to stay active/responsive while you sleep;
• The more you shut down, the more you have to wake up again to get back into "normal operation";
• The deeper you sleep, the longer it takes to wake again;
• Deeper sleep options often have more limited wakeup options;
• etc, etc, ...

As Simonr says, many (most?) of the SDK examples illustrate sleeping while waiting for events ...

[rookie]

Thanks awneil.

I have expanded on my question in my reply to simonr. My example is simple where I want to read a register. So What would be my options instead of waiting(using delay) for the twi handler to return an event to indicate a successful read.