This decreases the link time, especially on desktop machines with many CPU
cores. However, it does come at a slight cost in binary size, making the flash
section about 200 bytes bigger for circuitplayground_express.
Before, linking build-circuitplayground_express/firmware.elf takes
8.8s elapsed time, leaving 3128 bytes free in flash.
After, linking build-circuitplayground_express/firmware.elf takes 2.8s elapsed
time, leaving 2924 bytes free in flash. (-6 seconds, -204 bytes free)
If necessary, we can make this per-board or even per-translation to squeeze full
builds.
The issue was that a time.sleep() would set the RTC wake up
further into the future even if we wanted to tick every ms. Ticking
every ms is used to time the autoreload delay and without it,
autoreload doesn't work.
Fixes#3528
I have a function where it should be impossible to reach the end, so I put in a safe-mode reset at the bottom:
```
int find_unused_slot(void) {
// precondition: you already verified that a slot was available
for (int i=0; i<NUM_SLOTS; i++) {
if( slot_free(i)) {
return i;
}
}
safe_mode_reset(MICROPY_FATAL_ERROR);
}
```
However, the compiler still gave a diagnostic, because safe_mode_reset was not declared NORETURN.
So I started by teaching the compiler that reset_into_safe_mode never returned. This leads at least one level deeper due to reset_cpu needing to be a NORETURN function. Each port is a little different in this area. I also marked reset_to_bootloader as NORETURN.
Additional notes:
* stm32's reset_to_bootloader was not implemented, but now does a bare reset. Most stm32s are not fitted with uf2 bootloaders anyway.
* ditto cxd56
* esp32s2 did not implement reset_cpu at all. I used esp_restart(). (not tested)
* litex did not implement reset_cpu at all. I used reboot_ctrl_write. But notably this is what reset_to_bootloader already did, so one or the other must be incorrect (not tested). reboot_ctrl_write cannot be declared NORETURN, as it returns unless the special value 0xac is written), so a new unreachable forever-loop is added.
* cxd56's reset is via a boardctl() call which can't generically be declared NORETURN, so a new unreacahble "for(;;)" forever-loop is added.
* In several places, NVIC_SystemReset is redeclared with NORETURN applied. This is accepted just fine by gcc. I chose this as preferable to editing the multiple copies of CMSIS headers where it is normally declared.
* the stub safe_mode reset simply aborts. This is used in mpy-cross.
