1 files changed, 28 insertions, 2 deletions

diff --git a/ports/rp2/machine_timer.c b/ports/rp2/machine_timer.c
index 6f8b04f10e..ffb4c70243 100644
--- a/ports/rp2/machine_timer.c
+++ b/ports/rp2/machine_timer.c
@@ -27,6 +27,7 @@
 #include "py/runtime.h"
 #include "py/mperrno.h"
 #include "py/mphal.h"
+#include "py/gc.h"
 #include "pico/time.h"
 
 #define ALARM_ID_INVALID (-1)
@@ -40,13 +41,36 @@ typedef struct _machine_timer_obj_t {
     uint32_t mode;
     uint64_t delta_us; // for periodic mode
     mp_obj_t callback;
+    bool ishard;
 } machine_timer_obj_t;
 
 const mp_obj_type_t machine_timer_type;
 
 static int64_t alarm_callback(alarm_id_t id, void *user_data) {
     machine_timer_obj_t *self = user_data;
-    mp_sched_schedule(self->callback, MP_OBJ_FROM_PTR(self));
+
+    if (self->ishard) {
+        // When executing code within a handler we must lock the scheduler to
+        // prevent any scheduled callbacks from running, and lock the GC to
+        // prevent any memory allocations.
+        mp_sched_lock();
+        gc_lock();
+        nlr_buf_t nlr;
+        if (nlr_push(&nlr) == 0) {
+            mp_call_function_1(self->callback, MP_OBJ_FROM_PTR(self));
+            nlr_pop();
+        } else {
+            // Uncaught exception; disable the callback so it doesn't run again.
+            self->mode = TIMER_MODE_ONE_SHOT;
+            mp_printf(MICROPY_ERROR_PRINTER, "uncaught exception in timer callback\n");
+            mp_obj_print_exception(MICROPY_ERROR_PRINTER, MP_OBJ_FROM_PTR(nlr.ret_val));
+        }
+        gc_unlock();
+        mp_sched_unlock();
+    } else {
+        mp_sched_schedule(self->callback, MP_OBJ_FROM_PTR(self));
+    }
+
     if (self->mode == TIMER_MODE_ONE_SHOT) {
         return 0;
     } else {
@@ -66,13 +90,14 @@ static void machine_timer_print(const mp_print_t *print, mp_obj_t self_in, mp_pr
 }
 
 static mp_obj_t machine_timer_init_helper(machine_timer_obj_t *self, size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
-    enum { ARG_mode, ARG_callback, ARG_period, ARG_tick_hz, ARG_freq, };
+    enum { ARG_mode, ARG_callback, ARG_period, ARG_tick_hz, ARG_freq, ARG_hard, };
     static const mp_arg_t allowed_args[] = {
         { MP_QSTR_mode,         MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = TIMER_MODE_PERIODIC} },
         { MP_QSTR_callback,     MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_NONE} },
         { MP_QSTR_period,       MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 0xffffffff} },
         { MP_QSTR_tick_hz,      MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 1000} },
         { MP_QSTR_freq,         MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_NONE} },
+        { MP_QSTR_hard,         MP_ARG_KW_ONLY | MP_ARG_BOOL, {.u_bool = false} },
     };
 
     // Parse args
@@ -96,6 +121,7 @@ static mp_obj_t machine_timer_init_helper(machine_timer_obj_t *self, size_t n_ar
     }
 
     self->callback = args[ARG_callback].u_obj;
+    self->ishard = args[ARG_hard].u_bool;
     self->alarm_id = alarm_pool_add_alarm_in_us(self->pool, self->delta_us, alarm_callback, self, true);
     if (self->alarm_id == -1) {
         mp_raise_OSError(MP_ENOMEM);