Sleep interrupted by Portb, can I find out sleep time left?

[picnic]

I'm doing the age old thing of going to sleep and using the WDT to wake up PIC. I count n goes and then trundle off and do something useful.

I've now had to add a change on port B event to wake from sleep. I need to service that event and then continue sleeping until the sleep count expires to do the useful stuff as before.

I can detect the difference between being woken up from the Port B Interrupt and from the WDT timeout. However if I count the Port B events I do my useful stuff too early and if I ignore the Port B events for my loop counter then I'm late.

Is there a timer or other register that I can read and see how much of my WDT period was left when I get woken up by the port b int? I could then take into account these partial periods and still do my useful stuff at about the same time.

TIA

[FvM]

You'll surely have noticed, that there's no elapsed time information available from the WDT. The only practical method without starting a real timer is to split the WDT period into smaller slices and count these events, start the original wakeup code every 8, 16 or so events.

[picnic]

That was my conclusion but I had hoped I had missed something. Thanks.

[Ttelmah]

Worth realising that the watchdog does not give anything approaching an accurate time anyway. On 90% of chips it varies by as much as 300% depending on temperature, and supply voltage... On these chips the WDT, is just a capacitor discharge circuit.
On some later chips the WDT instead uses a counter running from the LF internal clock. On these there is a counter, but not available to you.
If pins are available, the only way to get this type of functionality, is to add a watch crystal to timer1, don't use the watchdog, and instead wake on the timer. This can then be read to see how long remains.

Best Wishes