Instead of actually defining each unused handler as an individual
"function" with an infinite loop, make them all reference the default
handler.  This shaves 192 bytes of unnecessary bloat off the .text
section.

Currently, misbehaving l0dables which trigger some kind of CPU exception
will busy-spin in the exception handler with no way to return to another
app without a full reboot.

Fix this by calling epic_exit() in case of an exception to hopefully
allow a return to menu in most situations.

After main() returns, don't enter a busy loop but call epic_exit() to
signal to epicardium that the l0dable has finished.  The exit code will
be the return value from main().

Signed-off-by: Rahix <rahix@rahix.de>

The new LEDs implementation already does gamma correction so it is
unnecessarily duplicated here now.  This commit also adds a short hello
message on the serial and sets the dim factor for the LEDs to a value
where the LED effect is more visible.

Signed-off-by: Rahix <rahix@rahix.de>

The vector table's alignment requirements depend on the number of
interrupts [1].  In our case, we have 0x6E(=110) interrupts and thus an
alignment requirement of 0x80(=128).

To satisfy this requirement, this commit moves the IVT to the beginning
of .text and enforces a 128 byte alignment.  Please note that the
headers which come before .text will push the IVT to 0x100 instead of
having it directly in the beginning at 0x00.

[1]: https://developer.arm.com/docs/dui0553/a/cortex-m4-peripherals/system-control-block/vector-table-offset-register



Signed-off-by: Rahix <rahix@rahix.de>

Signed-off-by: Rahix <rahix@rahix.de>

This lets us decide where the stack live, and place it at the best
possible spot for it to grow towards the image.

This is the first step towards having a heap in l0dables.