Put the core to rest, do not spin

Makefile

@@ -8,7 +8,7 @@ ENABLE_CLANG                  ?= 0
 ENABLE_SWD                    ?= 0
 ENABLE_OVERLAY                ?= 0
 ENABLE_LTO                    ?= 1
-
+ENABLE_WFI                    ?= 1
 # ---- STOCK QUANSHENG FERATURES ----
 ENABLE_UART                   ?= 1
 ENABLE_AIRCOPY                ?= 0
@@ -365,6 +365,9 @@ ifeq ($(ENABLE_FLASHLIGHT),1)
 	CFLAGS  += -DENABLE_FLASHLIGHT
 endif
 
+ifeq ($(ENABLE_WFI),1)
+	CFLAGS  += -DENABLE_WFI
+endif
 LDFLAGS =
 LDFLAGS += -z noexecstack -mcpu=cortex-m0 -nostartfiles -Wl,-T,firmware.ld -Wl,--gc-sections
 

driver/bk4819.c

@@ -16,13 +16,15 @@
 
 #include <stdio.h>   // NULL
 
-#include "audio.h"
+#include "../audio.h"
+#include "../bsp/dp32g030/gpio.h"
+#include "../bsp/dp32g030/portcon.h"
+
 #include "bk4819.h"
-#include "bsp/dp32g030/gpio.h"
-#include "bsp/dp32g030/portcon.h"
-#include "driver/gpio.h"
-#include "driver/system.h"
-#include "driver/systick.h"
+#include "gpio.h"
+#include "system.h"
+#include "systick.h"
+
 
 #ifndef ARRAY_SIZE
 	#define ARRAY_SIZE(x) (sizeof(x) / sizeof(x[0]))
@@ -127,7 +129,6 @@ static uint16_t BK4819_ReadU16(void)
 	PORTCON_PORTC_IE = (PORTCON_PORTC_IE & ~PORTCON_PORTC_IE_C2_MASK) | PORTCON_PORTC_IE_C2_BITS_ENABLE;
 	GPIOC->DIR = (GPIOC->DIR & ~GPIO_DIR_2_MASK) | GPIO_DIR_2_BITS_INPUT;
 	SYSTICK_DelayUs(1);
-
 	Value = 0;
 	for (i = 0; i < 16; i++)
 	{

driver/system.c

@@ -14,10 +14,10 @@
  *     limitations under the License.
  */
 
-#include "bsp/dp32g030/pmu.h"
-#include "bsp/dp32g030/syscon.h"
-#include "driver/system.h"
-#include "driver/systick.h"
+#include "../bsp/dp32g030/pmu.h"
+#include "../bsp/dp32g030/syscon.h"
+#include "system.h"
+#include "systick.h"
 
 void SYSTEM_DelayMs(uint32_t Delay)
 {

driver/systick.c

@@ -15,8 +15,8 @@
  */
 
 #include "ARMCM0.h"
-#include "driver/systick.h"
-#include "misc.h"
+#include "systick.h"
+#include "../misc.h"
 
 // 0x20000324
 static uint32_t gTickMultiplier;
@@ -29,17 +29,28 @@ void SYSTICK_Init(void)
 
 void SYSTICK_DelayUs(uint32_t Delay)
 {
-	const uint32_t ticks    = Delay * gTickMultiplier;
-	uint32_t       i        = 0;
-	uint32_t       Start    = SysTick->LOAD;
-	uint32_t       Previous = SysTick->VAL;
+	const uint32_t ticks = Delay * gTickMultiplier;
+	uint32_t elapsed_ticks = 0;
+	uint32_t Start = SysTick->LOAD;
+	uint32_t Previous = SysTick->VAL;
 	do {
 		uint32_t Current;
-		uint32_t Delta;
-		while ((Current = SysTick->VAL) == Previous) {}
-		Delta    = (Current < Previous) ? -Current : Start - Current;
-		i       += Delta + Previous;
+
+		do {
+			Current = SysTick->VAL;
+		} while (Current == Previous);
+
+		uint32_t Delta = ((Current < Previous) ? - Current : Start - Current);
+
+		elapsed_ticks += Delta + Previous;
+
 		Previous = Current;
-	} while (i < ticks);
-}
 
+#ifdef ENABLE_WFI
+		if (((int32_t)(ticks - elapsed_ticks)) >= 48 * 10000) {
+			__WFI();
+		}
+#endif
+
+	} while (elapsed_ticks < ticks);
+}

main.c

@@ -14,18 +14,27 @@
  *     limitations under the License.
  */
 
+#include <stdint.h>
 #include <string.h>
 #include <stdio.h>     // NULL
 
+#include "ARMCM0.h"
+
 #ifdef ENABLE_AM_FIX
 	#include "am_fix.h"
 #endif
+#include "misc.h"
+#include "radio.h"
+#include "settings.h"
+#include "version.h"
+#include "board.h"
+#include "audio.h"
+
 #include "app/app.h"
 #include "app/dtmf.h"
-#include "audio.h"
 #include "bsp/dp32g030/gpio.h"
 #include "bsp/dp32g030/syscon.h"
-#include "board.h"
+
 #include "driver/backlight.h"
 #include "driver/bk4819.h"
 #include "driver/gpio.h"
@@ -34,16 +43,13 @@
 #ifdef ENABLE_UART
 	#include "driver/uart.h"
 #endif
+
 #include "helper/battery.h"
 #include "helper/boot.h"
-#include "misc.h"
-#include "radio.h"
-#include "settings.h"
+
 #include "ui/lock.h"
 #include "ui/welcome.h"
 #include "ui/menu.h"
-#include "version.h"
-
 void _putchar(__attribute__((unused)) char c)
 {
 
@@ -102,9 +108,9 @@ void Main(void)
 
 	BATTERY_GetReadings(false);
 
-	#ifdef ENABLE_AM_FIX
-		AM_fix_init();
-	#endif
+#ifdef ENABLE_AM_FIX
+	AM_fix_init();
+#endif
 
 	const BOOT_Mode_t  BootMode = BOOT_GetMode();
 
@@ -215,18 +221,25 @@ void Main(void)
 		// ******************
 	}
 
-	while (1)
-	{
+	while (true) {
 		APP_Update();
-
-		if (gNextTimeslice)
-		{
+#ifdef ENABLE_WFI
+		/*
+		 * Do not spin mindlessly. Wait until the next interrupt is raised.
+		 * Could be SysTick, then gNextTimeslice would be true, or maybe there's
+		 * something else that is seeking attention that would or should be handled
+		 * by APP_Update(), who knows...
+		 * Longest-case-scenario: we are woken up by SysTick, and this loop runs at 10Mhz.
+		 * Should save quite a bit of battery, I guess.
+		*/
+		__WFI();
+#endif
+		if (gNextTimeslice) {
 			APP_TimeSlice10ms();
 			gNextTimeslice = false;
 		}
 
-		if (gNextTimeslice_500ms)
-		{
+		if (gNextTimeslice_500ms) {
 			APP_TimeSlice500ms();
 			gNextTimeslice_500ms = false;
 		}