Wake on ANT activity?

[AndrewM]

I'm trying to have an nrf51422 using S210 go to sleep and wait until it gets a signal from another ANT device to wake up. The other ANT device (master) will not always be on.

When the master turns off, the slave ANT device drops into search for a few seconds (I turned this down to minimum time) and then goes to sleep.

Is there a good way to wake up the slave device? I'd rather not keep it in search mode constantly. Is there a way to wake it on radio activity and then put it in search mode?

Using a timer to periodically wake the slave and put it in search mode for a few seconds is also not practical. I need it to wake up as soon as possible when it receives the master signal, and use as little power as possible when the master is not transmitting.

Thanks

[Harrison Chin]

In order to detect radio activity your slave will need to search.

It may be lower power to instead keep the channel between your master and slave open at the largest possible channel period instead, and then use a message to speed the up the channel or open a faster channel when necessary.

[David Smoot]

You have to receive radio signals to respond to them. Receiving signals means the radio must be on, which burns power.

Unless you have some mechanism to know exactly when to listen, you have no choice in the matter.

If you control both sides, Master and Slave, you can implement some adaptive clocking of transmissions to minimize power. But if you need to respond quickly to a master that is arriving at an unknown time, there is no choice to listen often.