diff --git a/ports/samd/modmachine.c b/ports/samd/modmachine.c
index 21d700ac31..db3f159cc2 100644
--- a/ports/samd/modmachine.c
+++ b/ports/samd/modmachine.c
@@ -139,6 +139,17 @@ STATIC mp_obj_t machine_enable_irq(mp_obj_t state_in) {
 }
 MP_DEFINE_CONST_FUN_OBJ_1(machine_enable_irq_obj, machine_enable_irq);
 
+STATIC mp_obj_t machine_reset_cause(void) {
+    #if defined(MCU_SAMD21)
+    return MP_OBJ_NEW_SMALL_INT(PM->RCAUSE.reg);
+    #elif defined(MCU_SAMD51)
+    return MP_OBJ_NEW_SMALL_INT(RSTC->RCAUSE.reg);
+    #else
+    return MP_OBJ_NEW_SMALL_INT(0);
+    #endif
+}
+MP_DEFINE_CONST_FUN_OBJ_0(machine_reset_cause_obj, machine_reset_cause);
+
 STATIC const mp_rom_map_elem_t machine_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR___name__),            MP_ROM_QSTR(MP_QSTR_umachine) },
     { MP_ROM_QSTR(MP_QSTR_reset),               MP_ROM_PTR(&machine_reset_obj) },
@@ -165,8 +176,18 @@ STATIC const mp_rom_map_elem_t machine_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR_idle),                MP_ROM_PTR(&machine_idle_obj) },
     { MP_ROM_QSTR(MP_QSTR_disable_irq),         MP_ROM_PTR(&machine_disable_irq_obj) },
     { MP_ROM_QSTR(MP_QSTR_enable_irq),          MP_ROM_PTR(&machine_enable_irq_obj) },
+    { MP_ROM_QSTR(MP_QSTR_reset_cause),         MP_ROM_PTR(&machine_reset_cause_obj) },
     { MP_ROM_QSTR(MP_QSTR_time_pulse_us),       MP_ROM_PTR(&machine_time_pulse_us_obj) },
     { MP_ROM_QSTR(MP_QSTR_bitstream),           MP_ROM_PTR(&machine_bitstream_obj) },
+
+    // Class constants.
+    // Use numerical constants instead of the symbolic names,
+    // since the names differ between SAMD21 and SAMD51.
+    { MP_ROM_QSTR(MP_QSTR_PWRON_RESET),         MP_ROM_INT(0x01) },
+    { MP_ROM_QSTR(MP_QSTR_HARD_RESET),          MP_ROM_INT(0x10) },
+    { MP_ROM_QSTR(MP_QSTR_WDT_RESET),           MP_ROM_INT(0x20) },
+    { MP_ROM_QSTR(MP_QSTR_SOFT_RESET),          MP_ROM_INT(0x40) },
+    { MP_ROM_QSTR(MP_QSTR_DEEPSLEEP_RESET),     MP_ROM_INT(0x80) },
 };
 STATIC MP_DEFINE_CONST_DICT(machine_module_globals, machine_module_globals_table);