AN4503: Do I really need to enable a falling edge interrupt?

[markosiponen]

In the AN4503 they activate a falling edge interrupt on the E1 pin. Do I really need to do that to be able to wake up on a falling edge on that pin?

It is not enough to do the following:

LLWU_PE1 = LLWU_PE1_WUPE0(2); //falling edge detection

[Monica]

Hello Markosiponen,

have there been any breakthroughs? Please keep us posted :smileywink:

Best regards,

Monica

[markosiponen · Accepted solution]

Yes it works without the interrupt enabled :-)

But first it didn't wake up as expected, it got stuck. But then I found information on this forum that the ACKISO bit must be cleared before configuring the oscillators. This information should be better explained in some manual I think.

https://community.freescale.com/message/335723#335723

[philip_drake]

Hello again,

I'm glad it is working.  Sorry about the ACKISO issue.

So there really two different hold types 1) I/O hold that happens in STOP, VLPS, and LLS that release automatically and 2) I/O and OSC hold that only  is released with the write to ACKISO.

Say you have the Oscillator and GPIO set up before going inteo VLLS1.  Some of the GPIO are outputs driving low and the OSC is enabled to be running in the low power mode.  After the wakeup event the MCU exits the low power mode through the reset flow if waking from VLLSx low power modes. The set up for the OSC and GPIO are lost with the reset, but until you write the ACKISO bit, the pins are held in state and the oscillator will continue to oscillate. The output will continue to be same output state at the pin while you are in the low power mode. Upon wakeup, in order not to glitch you I/O and stop your OSC for the short time between the ACKISO and re-initializing the I/O and OSC it is recommended to complete the I/O and module initialization and re-write the OSC registers in either  the OSC block or MCG prior to writing the ACKISO bit.  For the output driving low, you would re-run the setup code that initialized the GPIO, initialize the UART or timer output, or other peripherals that can control or be sensitive to pins prior to the write to ACKISO.

By the way, ACKISO, or the hold of pin state, is a feature that has been available for many years on Freescale MCU's including the S08 and CFV1 devices.

Best Regards,

[philip_drake]

Hello Mark, 

If you are going into a low power mode like LLS or VLLS0,1,2,3 then you absolutely do not need the Port interrupt enabled to have the pin be an LLWU wakeup.  If you did, however, the act of clearing the LLWU flag in the LLWU interrupt routine clears the port ICF flag.  Plus if you enabled the interrupt and you were going into VLPS, STOP, VLPR or WAIT the port interrupt would be available to do something differently than the wakeup from LLS. 

The only requiremnt for the LLWU wakeup event to occur is for the pin to be muxed as a digital pin as indicated in Wake-up sources in section 3 of the RM

"LLWU_P0-15 are external pin inputs. Any digital function multiplexed on the pin

can be selected as the wakeup source. See the chip's signal multiplexing table for the

digital signal options."

I hope this helps

Philip