Let a variant override sleep

.. & do so in the sound build, so audio can continue during
a time.sleep call

ports/unix/modtime.c

@@ -34,6 +34,7 @@
 
 #include "py/mphal.h"
 #include "py/runtime.h"
+#include "modtime.h"
 
 #ifdef _WIN32
 static inline int msec_sleep_tv(struct timeval *tv) {
@@ -85,7 +86,8 @@ static mp_obj_t mod_time_clock(void) {
 }
 static MP_DEFINE_CONST_FUN_OBJ_0(mod_time_clock_obj, mod_time_clock);
 
-static mp_obj_t mp_time_sleep(mp_obj_t arg) {
+MP_WEAK // CIRCUITPY-CHANGE: function is weak
+mp_obj_t mp_time_sleep(mp_obj_t arg) {
     #if MICROPY_PY_BUILTINS_FLOAT
     struct timeval tv;
     mp_float_t val = mp_obj_get_float(arg);

ports/unix/modtime.h

@@ -0,0 +1,4 @@
+#pragma once
+#include "py/obj.h"
+
+mp_obj_t mp_time_sleep(mp_obj_t arg);

ports/unix/variants/sound/modtime.c

@@ -0,0 +1,24 @@
+#include "py/mpconfig.h"
+#include "py/mpthread.h"
+#include "py/runtime.h"
+#include "modtime.h"
+#include <math.h>
+#include <sys/select.h>
+
+mp_obj_t mp_time_sleep(mp_obj_t arg) {
+    #if MICROPY_PY_BUILTINS_FLOAT
+    uint64_t interval = (uint64_t)MICROPY_FLOAT_C_FUN(round)(mp_obj_get_float(arg) * 1e3);
+    #else
+    uint64_t interval = UINT64_C(1000) * mp_obj_get_int(arg);
+    #endif
+
+    for (; interval--;) {
+        struct timeval tv = { .tv_sec = 0, .tv_usec = 1000};
+        MP_THREAD_GIL_EXIT();
+        (void)select(0, NULL, NULL, NULL, &tv);
+        MP_THREAD_GIL_ENTER();
+        RUN_BACKGROUND_TASKS;
+        mp_handle_pending(true);
+    }
+    return mp_const_none;
+}

ports/unix/variants/sound/mpconfigvariant.mk

@@ -28,6 +28,7 @@ SRC_C += lib/tjpgd/src/tjpgd.c
 $(BUILD)/lib/tjpgd/src/tjpgd.o: CFLAGS += -Wno-shadow -Wno-cast-align
 
 SRC_CIRCUITPYTHON := \
+	variants/sound/modtime.c \
 	shared/runtime/context_manager_helpers.c \
 	displayio_min.c \
 	shared-bindings/__future__/__init__.c \