py: Add MICROPY_KBD_EXCEPTION config option to provide mp_kbd_exception.

Defining and initialising mp_kbd_exception is boiler-plate code and so the
core runtime can provide it, instead of each port needing to do it
themselves.

The exception object is placed in the VM state rather than on the heap.

py/mpconfig.h

@@ -446,6 +446,11 @@
 #   endif
 #endif
 
+// Whether to provide the mp_kbd_exception object
+#ifndef MICROPY_KBD_EXCEPTION
+#define MICROPY_KBD_EXCEPTION (0)
+#endif
+
 // Prefer to raise KeyboardInterrupt asynchronously (from signal or interrupt
 // handler) - if supported by a particular port.
 #ifndef MICROPY_ASYNC_KBD_INTR

py/mpstate.h

@@ -118,6 +118,11 @@ typedef struct _mp_state_vm_t {
     #endif
     #endif
 
+    #if MICROPY_KBD_EXCEPTION
+    // exception object of type KeyboardInterrupt
+    mp_obj_exception_t mp_kbd_exception;
+    #endif
+
     // dictionary with loaded modules (may be exposed as sys.modules)
     mp_obj_dict_t mp_loaded_modules_dict;
 

py/runtime.c

@@ -68,6 +68,15 @@ void mp_init(void) {
     mp_init_emergency_exception_buf();
 #endif
 
+    #if MICROPY_KBD_EXCEPTION
+    // initialise the exception object for raising KeyboardInterrupt
+    MP_STATE_VM(mp_kbd_exception).base.type = &mp_type_KeyboardInterrupt;
+    MP_STATE_VM(mp_kbd_exception).traceback_alloc = 0;
+    MP_STATE_VM(mp_kbd_exception).traceback_len = 0;
+    MP_STATE_VM(mp_kbd_exception).traceback_data = NULL;
+    MP_STATE_VM(mp_kbd_exception).args = mp_const_empty_tuple;
+    #endif
+
     // call port specific initialization if any
 #ifdef MICROPY_PORT_INIT_FUNC
     MICROPY_PORT_INIT_FUNC;