esp8266/modmachine: Use common machine_time_pulse_us implementation.

Testing shows that for frequencies which the esp8266 can handle -- up to
about 1kHz -- `machine.time_pulse_us()` now gives more accurate results.

Prior to this commit it would measure on average about 1us lower, but now
the average is much closer to the true value.  For example a pulse that is
1000us long, it would measure between 998 and 1000us.  Now it measures
between 999us and 1001us.

Signed-off-by: Damien George <damien@micropython.org>

Author: dpgeorge

extmod/machine_pulse.c

@@ -30,7 +30,7 @@
 
 #if MICROPY_PY_MACHINE_PULSE
 
-MP_WEAK mp_uint_t machine_time_pulse_us(mp_hal_pin_obj_t pin, int pulse_level, mp_uint_t timeout_us) {
+mp_uint_t machine_time_pulse_us(mp_hal_pin_obj_t pin, int pulse_level, mp_uint_t timeout_us) {
     mp_uint_t nchanges = 2;
     mp_uint_t start = mp_hal_ticks_us();
     for (;;) {

ports/esp8266/esp_mphal.h

@@ -27,11 +27,20 @@
 #include "user_interface.h"
 #include "py/ringbuf.h"
 #include "shared/runtime/interrupt_char.h"
+#include "ets_alt_task.h"
 #include "xtirq.h"
 
 #define MICROPY_BEGIN_ATOMIC_SECTION() esp_disable_irq()
 #define MICROPY_END_ATOMIC_SECTION(state) esp_enable_irq(state)
 
+// During machine.time_pulse_us, feed WDT every now and then.
+#define MICROPY_PY_MACHINE_TIME_PULSE_US_HOOK(dt) \
+    do { \
+        if ((dt & 0xffff) == 0xffff && !ets_loop_dont_feed_sw_wdt) { \
+            system_soft_wdt_feed(); \
+        } \
+    } while (0)
+
 void mp_sched_keyboard_interrupt(void);
 
 struct _mp_print_t;

ports/esp8266/modmachine.c

@@ -33,7 +33,6 @@
 #include "os_type.h"
 #include "osapi.h"
 #include "etshal.h"
-#include "ets_alt_task.h"
 #include "user_interface.h"
 
 // #define MACHINE_WAKE_IDLE (0x01)
@@ -327,32 +326,3 @@ MP_DEFINE_CONST_OBJ_TYPE(
     print, esp_timer_print,
     locals_dict, &esp_timer_locals_dict
     );
-
-// Custom version of this function that feeds system WDT if necessary
-mp_uint_t machine_time_pulse_us(mp_hal_pin_obj_t pin, int pulse_level, mp_uint_t timeout_us) {
-    int nchanges = 2;
-    uint32_t start = system_get_time(); // in microseconds
-    for (;;) {
-        uint32_t dt = system_get_time() - start;
-
-        // Check if pin changed to wanted value
-        if (mp_hal_pin_read(pin) == pulse_level) {
-            if (--nchanges == 0) {
-                return dt;
-            }
-            pulse_level = 1 - pulse_level;
-            start = system_get_time();
-            continue;
-        }
-
-        // Check for timeout
-        if (dt >= timeout_us) {
-            return (mp_uint_t)-nchanges;
-        }
-
-        // Only feed WDT every now and then, to make sure edge timing is accurate
-        if ((dt & 0xffff) == 0xffff && !ets_loop_dont_feed_sw_wdt) {
-            system_soft_wdt_feed();
-        }
-    }
-}