[python] Use a custom modtime implementation

It only exposes "monotonic" and "sleep" functions, which are the
only part of CPython's time we can actually do at the moment.

python/port/genhdr/qstrdefs.in.h

@@ -27,8 +27,7 @@ Q(set_pixel)
 // utime QSTRs
 Q(time)
 Q(sleep)
-Q(time)
-Q(clock)
+Q(monotonic)
 
 // MicroPython QSTRs
 Q()

python/port/modtime.c

@@ -0,0 +1,42 @@
+#include <stdio.h>
+#include <string.h>
+
+#include "py/smallint.h"
+#include "py/runtime.h"
+
+#include "ion/timing.h"
+
+void delay_ms(mp_uint_t delay) {
+  uint32_t start = millis();
+  while (millis() - start < delay && !micropython_port_should_interrupt()) {
+    msleep(1);
+  }
+}
+
+STATIC mp_obj_t time_sleep(mp_obj_t seconds_o) {
+#if MICROPY_PY_BUILTINS_FLOAT
+  delay_ms((mp_uint_t)(1000 * mp_obj_get_float(seconds_o)));
+#else
+  delay_ms(1000 * mp_obj_get_int(seconds_o));
+#endif
+  return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_1(time_sleep_obj, time_sleep);
+
+STATIC mp_obj_t time_monotonic(void) {
+    return mp_obj_new_float(millis() / 1000.0);
+}
+MP_DEFINE_CONST_FUN_OBJ_0(time_monotonic_obj, time_monotonic);
+
+STATIC const mp_rom_map_elem_t time_module_globals_table[] = {
+  { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_time) },
+  { MP_ROM_QSTR(MP_QSTR_sleep), MP_ROM_PTR(&time_sleep_obj) },
+  { MP_ROM_QSTR(MP_QSTR_monotonic), MP_ROM_PTR(&time_monotonic_obj) },
+};
+
+STATIC MP_DEFINE_CONST_DICT(time_module_globals, time_module_globals_table);
+
+const mp_obj_module_t time_module = {
+  .base = { &mp_type_module },
+  .globals = (mp_obj_dict_t*)&time_module_globals,
+};