stmhal: Make pyb.[u]delay use systick with IRQs, busy loop otherwise.

pyb.delay and pyb.udelay now use systick if IRQs are enabled, otherwise
they use a busy loop.  Thus they work correctly when IRQs are disabled.
The busy loop is computed from the current CPU frequency, so works no
matter the CPU frequency.

1 files changed, 1 insertions, 4 deletions

diff --git a/stmhal/modpyb.c b/stmhal/modpyb.c
index 38c5499b0..46ce0e098 100644
--- a/stmhal/modpyb.c
+++ b/stmhal/modpyb.c
@@ -402,10 +402,7 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_1(pyb_delay_obj, pyb_delay);
 STATIC mp_obj_t pyb_udelay(mp_obj_t usec_in) {
     mp_int_t usec = mp_obj_get_int(usec_in);
     if (usec > 0) {
-        uint32_t count = 0;
-        const uint32_t utime = (168 * usec / 4);
-        while (++count <= utime) {
-        }
+        sys_tick_udelay(usec);
     }
     return mp_const_none;
 }