unix/modmachine: Add machine.idle(), implemented using sched_yield.

Also add a definition of MICROPY_EVENT_POLL_HOOK so the unix port can build
against modules that require this.

ports/unix/modmachine.c

@@ -77,6 +77,14 @@ uintptr_t mod_machine_mem_get_addr(mp_obj_t addr_o, uint align) {
     return addr;
 }
 
+#ifdef MICROPY_UNIX_MACHINE_IDLE
+STATIC mp_obj_t machine_idle(void) {
+    MICROPY_UNIX_MACHINE_IDLE
+    return mp_const_none;
+}
+MP_DEFINE_CONST_FUN_OBJ_0(machine_idle_obj, machine_idle);
+#endif
+
 STATIC const mp_rom_map_elem_t machine_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR___name__), MP_ROM_QSTR(MP_QSTR_umachine) },
 
@@ -84,6 +92,10 @@ STATIC const mp_rom_map_elem_t machine_module_globals_table[] = {
     { MP_ROM_QSTR(MP_QSTR_mem16), MP_ROM_PTR(&machine_mem16_obj) },
     { MP_ROM_QSTR(MP_QSTR_mem32), MP_ROM_PTR(&machine_mem32_obj) },
 
+    #ifdef MICROPY_UNIX_MACHINE_IDLE
+    { MP_ROM_QSTR(MP_QSTR_idle), MP_ROM_PTR(&machine_idle_obj) },
+    #endif
+
     { MP_ROM_QSTR(MP_QSTR_PinBase), MP_ROM_PTR(&machine_pinbase_type) },
     { MP_ROM_QSTR(MP_QSTR_Signal), MP_ROM_PTR(&machine_signal_type) },
     #if MICROPY_PY_MACHINE_PULSE

ports/unix/mpconfigport.h

@@ -349,4 +349,9 @@ void mp_unix_mark_exec(void);
 #define MICROPY_END_ATOMIC_SECTION(x) (void)x; mp_thread_unix_end_atomic_section()
 #endif
 
+#define MICROPY_EVENT_POLL_HOOK mp_hal_delay_us(500);
+
+#include <sched.h>
+#define MICROPY_UNIX_MACHINE_IDLE sched_yield();
+
 #endif // MICROPY_UNIX_MINIMAL