- Use compiler-rt and picolibc instead of avr-libc.
- Use ld.lld instead of avr-ld (or avr-gcc).
This makes it much easier to get started with TinyGo on AVR because
installing these extra tools (gcc-avr, avr-libc) can be a hassle.
It also opens the door for future improvements such as ThinLTO.
There is a code size increase but I think it's worth it in the long run.
The code size increase can hopefully be reduced with improvements to the
LLVM AVR backend and to compiler-rt.
This matches the flash-command and is generally a bit easier to work
with.
This commit also prepares for allowing multiple formats to be used in
the emulator command, which is necessary for the esp32.
It was `avr-atmel-none`, which is incorrect. It must be
`avr-unknown-unknown`.
Additionally, there is no reason to specify the target triple per chip,
it can be done for all AVR chips at once as it doesn't vary like
Cortex-M chips.
It does not appear to be necessary for these devices but might result in
more appropriate libraries to be linked in.
It is best to _not_ specify the exact MCU because otherwise a few other
settings (such as startfiles and some linker script configs) also get
set, which we do manually anyway and should not be interfered with.
I discovered this while working on support for the atmega1284.
Setting the linker script as one property (instead of as part of the
generic ldflags property) allows it to be overriden.
This is important for the SoftDevice on Nordic chips, because the
SoftDevice takes up a fixed part of the flash/RAM and the application
must be flashed at a different position. With this linkerscript option,
it is possible to create (for example) a pca10040-s132v6 that overrides
the default linker script.
Instead of specifying explicit commands, most of these commands have
been replaced by more specific properties.
This is work that will be necessary for an eventual -programmer flag to
the compiler, with which it is possible to select which programmer to
use to flash or debug a chip. That's not very useful for boards that
already include a programmer or bootloader for that purpose, but is very
useful for novel boards or single-purpose boards that are not already
included in TinyGo.
* all: add support for specifying target CPU in target config
* avr: specify the chip name in the target CPU
This reduces code size by a large margin. For examples/blinky, it
reduces code size from 1360 to 1266 when compiling for the Arduino Uno
(94 bytes, or ~7%).
