Connect buttons to interrupt pins

[charlespax]

We should connect each button and RTC_INT to an interrupt pin. This will give us the highest flexibility in user interface design.

In Electronics version 0.10 the interrupt pins available for swapping are PCINT4 on LCD_CS, PCINT5 on VBAT_SENSE, PCINT6 on VBAT_EN, PCINT7 on FLASH_CS, and PCINT0 on SD_CS.

Item	Function	Interrupt	Note
RTC_INT	Wake for readings	INT6	Requires interrupt
SW_A	Logging start/stop	INT3	Requires interrupt
SW_B	Logging interval	INT2	Probably does not need interrupt
SW_C	Temperature units	none	Should probably have interrupt
SW_D	Toggle channels	none	Should probably have interrupt
SW_E	Backlight	none	Should probably have interrupt
SW_PWR	Power	none	Should probably have interrupt

For a full pin map of Electronics version 0.10 see https://github.com/PaxInstruments/t400-electronics/issues/114.

[cibomahto]

The only place where it really matters if the pin can generate an input is when the processor is in sleep mode. When the device is running, it makes more sense to use a single timer interrupt to poll all of the buttons, to make the debounce routine more effective.

From the manual, here is the list of interrupt sources that can be used to wake the processor:

As noted above, RTC_INT, SW_A, and SW_B are all connected to dedicated hardware interrupts (INTx), so they are fine, and the other pins cannot be used to wake the processor. The two interrupt methods are separate peripherals- the pin change one will make an interrupt whenever the pin changes state (high-to-low and low-to-high), while the hardware interrupt can trigger on a low-to-high, high-to-low, or whenever the value is low. Either peripheral will work for waking up the t400.

The other buttons, also as noted above, aren't connected to an interrupt source and could not be used to wake the device from sleep.

[cibomahto]

Here are the pins with external interrupt capability:

PB0: PCINT0 PB1: PCINT1 PB2: PCINT2 PB3: PCINT3 PB4: PCINT4 PB5: PCINT5 PB6: PCINT6 PB7: PCINT7 PD0: INT0 PD1: INT1 PD2: INT2 PD3: INT3 PE6: INT6

From a software perspective, it's cumbersome to have to deal with both types at the same time, but it's not a showstopper.

[cibomahto]

Also note that the only interrupt that's capable of waking the system from sleep in the lowest power mode (all clocks off) is INT6, so placing the RTC interrupt on that line was a good call.

[charlespax]

The table indicates "INT6,INT3:0 and pin change" can wake the processor during any sleep mode while the ADC, for example, can only wake the processor from Idle and ADCNRM. Am I reading the table wrong?

[cibomahto]

You are reading it correctly. Some of the peripherals are disabled in some of the sleep modes, so they can't be used to turn on the processor.

Also, detecting pin change interrupts while in the power down mode will slightly increase power usage, as a clock has to be enabled for the pin change peripheral to work. The INT6 pin's 'low' interrupt can work without a clock. Those details shouldn't matter with this design, because the difference should be small compared to the small amount that the rest of the peripherals use.

[charlespax]

It looks like we'll never use the lowest level interrupt for RTC_INT. We would need at least one button on the same level, so a user can stop logging.

[charlespax]

It looks like we can get all the buttons and the RTC_INT pin on interrupts. Let's do this for the next version.

[charlespax]

This did not make it into the most recent board order. Moving to next milestone.

[samchoy88]

Here are the pins with external interrupt capability:

PB0: PCINT0 PB1: PCINT1 PB2: PCINT2 PB3: PCINT3 PB4: PCINT4 PB5: PCINT5 PB6: PCINT6 PB7: PCINT7 PD0: INT0 PD1: INT1 PD2: INT2 PD3: INT3 PE6: INT6

Below is the pin assignment of the layout in Rev 0.12

Item	Function	Interrupt	Note
RTC_INT	Wake for readings	INT6	PE6
SW_A	Logging start/stop	INT3	PD3
SW_B	Logging interval	INT2	PD2
SW_C	Temperature units	PCINT4	PB4
SW_D	Toggle channels	PCINT5	PB5
SW_E	Backlight	PCINT6	PB6
SW_PWR	Power	PCINT0	PB0

[charlespax]

Amazing!