Replace Nordic's appTimer with a driver for RTC1

[rgrover]

This requires careful review and testing. I've done a fair bit, but much more is needed.
This has been very tricky code owing mostly to:

• trickiness involved in manipulating lists from re-entrant functions in interrupt context.
• RTC counter being 24bit instead of 32bit.
• us_ticker API receiving time in microseconds, whereas RTC counting in units of 1/32Khz.

Please review and test. I have a suspicion extensive testing may reveal more hardware related quirks which haven't been taken care of.

[0xc0170]

Please remove the project header file, see Travis log : error for #include "projectconfig.h"

[0xc0170]

We should inform users who reported problems with previous implementation about this update, they can test this.
I would keep this open until we got some testing results here

[rgrover]

@0xc0170 could you please review the code? Either you or Bogdan?
thanks.

I'll also connect with the previous reporters.

[0xc0170]

Why is the function in capital letters? This can clash with macros

[0xc0170]

Can you describe this check ?

[0xc0170]

IS there a reason to call 2x us ticker , using 2 different invokes (RTC_UNITS_TO_MICROSECONDS(rtc1_getCounter() and us_ticker_read() ) ?

[rgrover]

you're correct. I'm duplicating work here. I could reuse the value from RTC_UNITS_TO_MICROSECONDS(rtc1_getCounter()) instead of calling us_ticker_read(). thanks.

[rgrover]

if ((us_ticker_read() > 0xF0000000) && (timestamp < 0x10000000)) {

the above check detects an attempt to set a timeout for a value which has wrapped around, but the attempt is being made at a time when the current RTC value when translated into microseconds hasn't wrapped around.

[0xc0170]

Is this duplication? The overflow is handled in rtc1_getCounter(), which is invoked meeting some conditions below. Can this be reorganized?

counter = rtc1_getCounter();
if (NRF_RTC1->EVENTS_COMPARE[0] && us_ticker_callbackPending && ((int)(us_ticker_callbackTimestamp - counter) <= 0))

[Sissors]

I think it does give a (small) chance on errors with really unlucky timing. When no interrupts can be handled (for example because it is in the Ticker interrupt routine), and between the check on the overflow flag and the reading of the timer it overflows it will use the new RTC value with the old overflow value.

As random example what I did once: https://github.com/mbedmicro/mbed/blob/master/libraries/mbed/targets/hal/TARGET_Freescale/TARGET_K20XX/us_ticker.c#L74. There are probably other options too.

[rgrover]

I'm using the following main.cpp to test my ticker for long periods of time.

#include "mbed.h"
#include "iBeaconService.h"

BLEDevice ble;

Ticker ticker1;
Ticker ticker2;

DigitalOut led1(LED1);
DigitalOut led2(LED2);

void periodicCallback1(void)
{
    led1 = !led1; /* Do blinky on LED1 while we're waiting for BLE events */
}

void periodicCallback2(void)
{
    led2 = !led2; /* Do blinky on LED2 while we're waiting for BLE events */
}

const uint8_t uuid[] = {0xE2, 0x0A, 0x39, 0xF4, 0x73, 0xF5, 0x4B, 0xC4,
                        0xA1, 0x2F, 0x17, 0xD1, 0xAD, 0x07, 0xA9, 0x61
                       };
uint16_t majorNumber = 1122;
uint16_t minorNumber = 3344;
uint16_t txPower = 0xC8;

int main(void)
{
    ble.init();

    ticker1.attach(periodicCallback1, 0.5);
    ticker2.attach(periodicCallback2, 0.25);

    iBeaconService ibeacon(ble, uuid, majorNumber, minorNumber, txPower);

    ble.setAdvertisingInterval(Gap::MSEC_TO_ADVERTISEMENT_DURATION_UNITS(1000)); /* 1000ms. */
    ble.startAdvertising();

    while(1) {
        ble.waitForEvent(); // allows or low power operation
    }
}