Turning SPI peripheral on/off from PPI

[cirlam]

I have an application working using PPI to start a SPI master transaction from a GPIOTE event. Unfortunately, I currently have very high current consumption which I am led to believe is because the SPI peripheral is always enabled. Can the SPI peripheral turned on/off using PPI?

I'd like to do the following: On GPIOTE event:

1. turn SPI peripheral on 2.Take Chip select low
2. start SPI transaction

On SPI stop event:

1. Take Chip Select High 2.Turn off SPI peripheral

I realise I can do this completely in software, but PPI seems like a very elegant and fast solution, so would like to use this if possible.

[Roger Clark]

From what I understand, nRF52 power management of peripherals is supposed to automatically turn off devices when they are not being used.

Are you sure the problem is SPI inside the nRF52 and not your peripheral.

Also GPIOTE events in fast mode are known to take a lot of power.

I know on the nRF51 that for GPIOTE to operate in fast mode, that it requires the HF oscillator to run. Hence for low power operation on the nRF51, GPIOTE needs to be set to Port Mode.

From what I have read, GPIOTE event current is still high on the nRF52 (see devzone.nordicsemi.com/.../)

Also see this errata infocenter.nordicsemi.com/index.jsp

[Stian Røed Hafskjold]

Roger Clark's answer is correct. It could be that the GPIOTE is in high accuracy mode. You should check out low accuracy mode and using the PORT event instead. And yes, you can use PPI to both start the TWI transaction and toggle a GPIO when it is done.

[cirlam]

Thanks for both of your responses. You are correct - I was using GPIOTE events in High accuracy mode. I was under the impression that these events are not horrendous in terms of current draw: devzone.nordicsemi.com/.../ However, it sounds like this isn't correct?

I actually have multiple sensors presenting a data ready interrupt. Can PORT events be used in this case - I presume there is no way for PPI to be able to distinguish between which pin (and therefore which sensor has data ready) triggered the PORT event?

[Stian Røed Hafskjold]

Yes, high accuracy mode consumes about 8uA when activated. When using low accuracy mode (= PORT event), the PPI will not be able to distinguish between between which pin triggered the event. You have to use a software interrupt handler for this.