This is a slight trade-off with code size, in places where a "_varg"
mp_raise variant is now used. The net savings on trinket_m0 is
just 32 bytes.
It also means that the translation will include the original English
text, and cannot be translated. These are usually names of Python
types such as int, set, or dict or special values such as "inf" or
"Nan".
The motivation for doing this is so that we can allow
common_hal_mcu_disable_interrupts in IRQ context, something that works
on other ports, but not on nRF with SD enabled. This is because
when SD is enabled, calling sd_softdevice_is_enabled in the context
of an interrupt with priority 2 or 3 causes a HardFault. We have chosen
to give the USB interrupt priority 2 on nRF, the highest priority that
is compatible with SD.
Since at least SoftDevice s130 v2.0.1, sd_nvic_critical_region_enter/exit
have been implemented as inline functions and are safe to call even if
softdevice is not enabled. Reference kindly provided by danh:
https://devzone.nordicsemi.com/f/nordic-q-a/29553/sd_nvic_critical_region_enter-exit-missing-in-s130-v2
Switching to these as the default/only way to enable/disable interrupts
simplifies things, and fixes several problems and potential problems:
* Interrupts at priority 2 or 3 could not call common_hal_mcu_disable_interrupts
because the call to sd_softdevice_is_enabled would HardFault
* Hypothetically, the state of sd_softdevice_is_enabled
could change from the disable to the enable call, meaning the calls
would not match (__disable_irq() could be balanced with
sd_nvic_critical_region_exit).
This also fixes a problem I believe would exist if disable() were called
twice when SD is enabled. There is a single "is_nested_critical_region"
flag, and the second call would set it to 1. Both of the enable()
calls that followed would call critical_region_exit(1), and interrupts
would not properly be reenabled. In the new version of the code,
we use our own nesting_count value to track the intended state, so
now nested disable()s only call critical_region_enter() once, only
updating is_nested_critical_region once; and only the second enable()
call will call critical_region_exit, with the right value of i_n_c_r.
Finally, in port_sleep_until_interrupt, if !sd_enabled, we really do
need to __disable_irq, rather than using the common_hal_mcu routines;
the reason why is documented in a comment.
