Merge pull request #109 from recallmenot/standby

standby + auto-wakeup example

examples/standby/Makefile

+all : flash
+
+TARGET:=standby
+
+CFLAGS+=-DSTDOUT_UART
+
+include ../../ch32v003fun/ch32v003fun.mk
+
+flash : cv_flash
+clean : cv_clean
+

examples/standby/README.md

+# the deepest slumber
+
+This example serves to show how to put the CH32V003 into its lowest power state (standby) and have it wake periodically.  
+
+Power consumption should be around 10uA.  
+
+The MCU only toggles the LED and prints a message, then it goes to sleep.  
+The LED staying on demonstrates that GPIO keeps its state even when the rest of the mcu is in a coma.  
+
+Based on the groundwork of Marek M.  
+
+## time calculations
+
+The autowakeup delay can be calculated by:
+
+`t = AWUWR / (fLSI / AWUPSC)`  
+
+Where AWUWR can be 1 to 63, fLSI is always 128000 and AWUPSC, for practical purposes is 2048, 4096, 10240 or 61440, though lower values are possible.  
+The maximum autowakeup delay is 30s.

examples/standby/standby.c

+// based on https://paste.sr.ht/blob/b9b4fb45cbc70f2db7e31a77a6ef7dd2a7f220fb
+// Could be defined here, or in the processor defines.
+#define SYSTEM_CORE_CLOCK 48000000
+
+#include "ch32v003fun.h"
+#include <stdio.h>
+
+#define APB_CLOCK SYSTEM_CORE_CLOCK
+
+/* somehow this ISR won't get called??
+void AWU_IRQHandler( void ) __attribute__((interrupt));
+void AWU_IRQHandler( void ) {
+	GPIOD->OUTDR ^= (1 << 4);
+}
+*/
+
+int main()
+{
+	SystemInit48HSI();
+	SetupUART( UART_BRR );
+
+	printf("\r\n\r\nlow power example\r\n\r\n");
+
+	RCC->APB2PCENR |= RCC_APB2Periph_GPIOD;
+	// GPIO D4 Push-Pull
+	GPIOD->CFGLR &= ~(0xf<<(4*4));
+	GPIOD->CFGLR |= (GPIO_Speed_10MHz | GPIO_CNF_OUT_PP)<<(4*4);
+	GPIOD->OUTDR |= (1 << 4);
+
+	// give the user time to open the terminal connection
+	//Delay_Ms(5000);
+	printf("5000ms wait over\r\n");
+	
+	// enable power interface module clock
+	RCC->APB1PCENR |= RCC_APB1Periph_PWR;
+
+	// enable low speed oscillator (LSI)
+	RCC->RSTSCKR |= RCC_LSION;
+	while ((RCC->RSTSCKR & RCC_LSIRDY) == 0) {}
+
+	// enable AutoWakeUp event
+	EXTI->EVENR |= EXTI_Line9;
+	EXTI->FTENR |= EXTI_Line9;
+
+	// configure AWU prescaler
+	PWR->AWUPSC |= PWR_AWU_Prescaler_4096;
+
+	// configure AWU window comparison value
+	PWR->AWUWR &= ~0x3f;
+	PWR->AWUWR |= 63;
+
+	// enable AWU
+	PWR->AWUCSR |= (1 << 1);
+
+	// select standby on power-down
+	PWR->CTLR |= PWR_CTLR_PDDS;
+
+	// peripheral interrupt controller send to deep sleep
+	PFIC->SCTLR |= (1 << 2);
+
+	uint16_t counter = 0;
+	printf("entering sleep loop\r\n");
+
+	for (;;) {
+		__WFE();
+		// restore clock to full speed
+		SystemInit48HSI();
+		printf("\r\nawake, %u\r\n", counter++);
+		GPIOD->OUTDR ^= (1 << 4);
+	}
+}