stmhal: Add "quiet timing" enter/exit functions.

They disable all interrupts except for SysTick and are useful for doing
certain low-level timing operations.

stmhal/irq.h

@@ -24,6 +24,9 @@
  * THE SOFTWARE.
  */
 
+#ifndef MICROPY_INCLUDED_STMHAL_IRQ_H
+#define MICROPY_INCLUDED_STMHAL_IRQ_H
+
 // these states correspond to values from query_irq, enable_irq and disable_irq
 #define IRQ_STATE_DISABLED (0x00000001)
 #define IRQ_STATE_ENABLED  (0x00000000)
@@ -147,4 +150,4 @@ MP_DECLARE_CONST_FUN_OBJ_0(pyb_irq_stats_obj);
 #define IRQ_PRI_RTC_WKUP        15
 #define IRQ_SUBPRI_RTC_WKUP                 0
 
-
+#endif // MICROPY_INCLUDED_STMHAL_IRQ_H

stmhal/mphalport.h

@@ -27,6 +27,10 @@ void mp_hal_set_interrupt_char(int c); // -1 to disable
 
 // timing functions
 
+#include "stmhal/irq.h"
+
+#define mp_hal_quiet_timing_enter() raise_irq_pri(1)
+#define mp_hal_quiet_timing_exit(irq_state) restore_irq_pri(irq_state)
 #define mp_hal_delay_us_fast(us) mp_hal_delay_us(us)
 
 extern bool mp_hal_ticks_cpu_enabled;