py: Add mp_pending_exception global variable, for VM soft interrupt.

This allows to implement KeyboardInterrupt on unix, and a much safer
ctrl-C in stmhal port.  First ctrl-C is a soft one, with hope that VM
will notice it; second ctrl-C is a hard one that kills anything (for
both unix and stmhal).

One needs to check for a pending exception in the VM only for jump
opcodes.  Others can't produce an infinite loop (infinite recursion is
caught by stack check).

1 files changed, 6 insertions, 0 deletions

diff --git a/py/runtime.c b/py/runtime.c
index 6cb5c7e19..f6f34be94 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -62,6 +62,9 @@
 #define DEBUG_OP_printf(...) (void)0
 #endif
 
+// pending exception object (MP_OBJ_NULL if not pending)
+mp_obj_t mp_pending_exception;
+
 // locals and globals need to be pointers because they can be the same in outer module scope
 STATIC mp_obj_dict_t *dict_locals;
 STATIC mp_obj_dict_t *dict_globals;
@@ -79,6 +82,9 @@ void mp_init(void) {
     qstr_init();
     mp_stack_ctrl_init();
 
+    // no pending exceptions to start with
+    mp_pending_exception = MP_OBJ_NULL;
+
 #if MICROPY_ENABLE_EMERGENCY_EXCEPTION_BUF
     mp_init_emergency_exception_buf();
 #endif