The old code was broken and led to a HardFault in a rather convoluted
way:
1. The CFA offset was incorrect, in fact it was not aligned (the stack
is supposed to always be aligned to 4 bytes at least).
2. This unaligned size was then used for stack size calculations.
3. A stack that wasn't a multiple of 4 was allocated.
4. The calleeSavedRegs struct (in `(internal/task.state).archInit`) was
not correctly aligned.
5. Writing to this struct resulted in a HardFault.
The previous commit started printing the instruction address for runtime
panics. This commit starts using this address to print the source
location.
Here is an example where this feature is very useful. There is a heap
allocation in the Bluetooth package, but we don't know where exactly.
Printing the instruction address of the panic is already useful, but
what is even more useful is looking up this address in the DWARF debug
information that's part of the binary:
$ tinygo flash -target=circuitplay-bluefruit -monitor ./examples/heartrate
Connected to /dev/ttyACM0. Press Ctrl-C to exit.
tick 00:00.810
tick 00:01.587
tick 00:02.387
tick 00:03.244
panic: runtime error at 0x00027c4d: alloc in interrupt
[tinygo: panic at /home/ayke/src/tinygo/bluetooth/adapter_sd.go:74:4]
To be clear, this path isn't stored on the microcontroller. It's stored
as part of the build, and `-monitor` just looks up the path from the
panic message.
Possible enhancements:
- Print such an address for regular panics as well. I'm not sure
that's so useful, as it's usually a lot easier to look up panics
just by their message.
- Use runtimePanicAt (instead of runtimePanic) in other locations, if
that proves to be beneficial.
- Print the TinyGo-generated output in some other color, to
distinguish it from the regular console output.
- Print more details when panicking (registers, stack values), and
print an actual backtrace.
This is not very useful in itself, but makes it possible to detect this
address in the output. See the next commit.
This adds around 50 bytes to each binary (except for AVR and wasm). This
is unfortunate, but I think this feature is quite useful still.
A future enhancement might be to create a build tag for extended panic
information that's not set by default.
Multisampling/averaging (using the Samples configuration property) was
returning incorrect values. When I investigated this, I found that the
samd51 gives erratic values when using multisampling together with fewer
than 16 bits resolution.
I fixed this by forcing 16 bit resolution when multisampling, and
adjusting the output to account for multisampling.
Found while reading the battery value on a pybadge, which gave
non-sensible values with Samples set to a value larger than 1.
This improves slightly. It also is some groundwork for better DMA
support in TinyGo in the future.
I'm not entirely sure why it improves performance (in theory the old
code should already saturate the SPI bus) but it does, so 🤷
The SPI frequency was rounded up, not rounded down. This meant that if
you wanted to configure 15MHz for example, it would pick the next
available frequency (24MHz). That's unsafe, the safe option is to round
down and the SPI support for most other chips also rounds down for this
reason.
In addition, I've improved SPI clock selection so that it will pick the
best clock of the two, widening the available frequencies. See the
comments in the patch for details.
I find myself consistently running tests, seeing them panic, and then
immediately running them again with this environment variable set. It's
easier to just have tinygo do this for me.
