The inline assembly implementation was badly in need of improvement.
- irq_disable() took 2 CPU cycles more than needed
- The current interrupt state was stored in a temporary register and
afterwards copied to the target register, rather than storing it in the
target register right away
- The lower bits of the state were cleared (as they have no meaning for the
interrupt status), but the API purposely never required such things from
implementations.
- irq_restore() took 5 CPU cycles. This was reduced to 3 CPU cycles (or 2 CPU
cycles in the best case)
When the SPI peripheral is disabled, the output lines will become HIGH-Z.
If the clk pin is not pulled HIGH or LOW, connected SPI slaves will start drawing current expectedly.
Since the "EXTI->PR" is an "rc_w1" type of register, we need to be
careful when clearing our interrupt flag in the register. When there
are multiple interrupt flags set in the register, the "|=" operation
will mistakenly clear all pending interrupts instead of just ours.
- On pwm_poweron, the PWM resolution was not restored. (A custom resolution was
only usable if, PWM channel 0 is not used. That configuration is not common,
so this bug was likely never triggered)
- Disabled a work around to prevent flickering:
- Previously, PWM was disconnected on level 0% and 100%
- This increases the run time of `pwm_set()`
- It prevents using the PWM for wave form generation via DDS, as the wave
noticeably jumps when reaching 0% or 100%
- Slightly reduces memory requirements: 2 Bytes of RAM, 112 Bytes of ROM
- Tested with avr-gcc 9.2.0 and LTO enabled
Drop `#include "irq.h"` in `cpu.h`, which was there for a legacy work around.
A bunch of missing includes of `irq.h` materialized due to this and were
fixed.
- Drop duplicated `cpu.c` and `cpu_conf.h`: Those are already provided by
`cpu/atmega_common`.
- The higher values for default stack size of `cpu_conf.h` in
`cpu/atmega_common` results in three tests no longer fitting the available RAM
==> Updated the Makefile.ci to skip linking of those tests for the Arduino
Leonardo
