esp8266/esp_mphal: Make atomic section more atomic.

By disabling ets_loop_iter when the atomic section is active.
Signed-off-by: Damien George <damien@micropython.org>

ports/esp8266/esp_mphal.c

@@ -166,6 +166,21 @@ void mp_hal_signal_dupterm_input(void) {
     system_os_post(DUPTERM_TASK_ID, 0, 0);
 }
 
+// this bit is unused in the Xtensa PS register
+#define ETS_LOOP_ITER_BIT (12)
+
+uint32_t esp_disable_irq(void) {
+    uint32_t state = disable_irq();
+    state = (state & ~(1 << ETS_LOOP_ITER_BIT)) | (ets_loop_iter_disable << ETS_LOOP_ITER_BIT);
+    ets_loop_iter_disable = 1;
+    return state;
+}
+
+void esp_enable_irq(uint32_t state) {
+    ets_loop_iter_disable = (state >> ETS_LOOP_ITER_BIT) & 1;
+    enable_irq(state & ~(1 << ETS_LOOP_ITER_BIT));
+}
+
 // Get pointer to esf_buf bookkeeping structure
 void *ets_get_esf_buf_ctlblk(void) {
     // Get literal ptr before start of esf_rx_buf_alloc func

ports/esp8266/mpconfigport.h

@@ -126,9 +126,8 @@
 #define MICROPY_VM_HOOK_LOOP MICROPY_VM_HOOK_POLL
 #define MICROPY_VM_HOOK_RETURN MICROPY_VM_HOOK_POLL
 
-#include "xtirq.h"
-#define MICROPY_BEGIN_ATOMIC_SECTION() disable_irq()
-#define MICROPY_END_ATOMIC_SECTION(state) enable_irq(state)
+#define MICROPY_BEGIN_ATOMIC_SECTION() esp_disable_irq()
+#define MICROPY_END_ATOMIC_SECTION(state) esp_enable_irq(state)
 
 // type definitions for the specific machine
 
@@ -173,3 +172,6 @@ extern const struct _mp_print_t mp_debug_print;
 #define WDEV_HWRNG ((volatile uint32_t *)0x3ff20e44)
 
 #define _assert(expr) ((expr) ? (void)0 : __assert_func(__FILE__, __LINE__, __func__, #expr))
+
+uint32_t esp_disable_irq(void);
+void esp_enable_irq(uint32_t state);