shared/runtime/pyexec: Make a raised SystemExit always do a forced exit.

The current situation with SystemExit and soft reset is the following:
- `sys.exit()` follows CPython and just raises `SystemExit`.
- On the unix port, raising `SystemExit` quits the application/MicroPython,
  whether at the REPL or in code (this follows CPython behaviour).
- On bare-metal ports, raising `SystemExit` at the REPL does nothing,
  raising it in code will stop the code and drop into the REPL.
- `machine.soft_reset()` raises `SystemExit` but with a special flag set,
  and bare-metal targets check this flag when it propagates to the
  top-level and do a soft reset when they receive it.

The original idea here was that a bare-metal target can't "quit" like the
unix port can, and so dropping to the REPL was considered the same as
"quit".  But this bare-metal behaviour is arguably inconsistent with unix,
and "quit" should mean terminate everything, including REPL access.

This commit changes the behaviour to the following, which is more
consistent:
- Raising `SystemExit` on a bare-metal port will do a soft reset (unless
  the exception is caught by the application).
- `machine.soft_reset()` is now equivalent to `sys.exit()`.
- unix port behaviour remains unchanged.

Tested running the test suite on an stm32 board and everything still
passes, in particular tests that skip by raising `SystemExit` still
correctly skip.

Signed-off-by: Damien George <damien@micropython.org>

1 files changed, 0 insertions, 3 deletions

diff --git a/ports/unix/modmachine.c b/ports/unix/modmachine.c
index 6f3ab8094..d1cdbe861 100644
--- a/ports/unix/modmachine.c
+++ b/ports/unix/modmachine.c
@@ -36,9 +36,6 @@
 #define MICROPY_PAGE_MASK (MICROPY_PAGE_SIZE - 1)
 #endif
 
-// This variable is needed for machine.soft_reset(), but the variable is otherwise unused.
-int pyexec_system_exit = 0;
-
 uintptr_t mod_machine_mem_get_addr(mp_obj_t addr_o, uint align) {
     uintptr_t addr = mp_obj_get_int_truncated(addr_o);
     if ((addr & (align - 1)) != 0) {