Add example for write to User Data0/1 in Option Bytes

examples/optiondata/Makefile

+all : flash
+
+TARGET:=optiondata
+
+include ../../ch32v003fun/ch32v003fun.mk
+
+flash : cv_flash
+clean : cv_clean

examples/optiondata/README.md

+# Write to the user fields in the Option Data flash
+
+This is a simple example code for writing to the two 8-bit data0/data1 bytes that are a part of the Flash "User-selected words" (aka Option bytes).
+
+To reduce the code footpint no timeouts are implemented in the code. It simply waits for the busy-flag to be cleaed. The two wait-loops could be replaced with a Delay_Ms(10) if speed is not an issue.
+
+The two bytes could be used for remembering user settings between power-offs.
+
+After flashing you can test it with the command
+`../../minichlink/minichlink -a -b -T` 
+that will Halt, Reboot and enter Terminal mode. For each run the count will increment by one.

examples/optiondata/optiondata.c

+//
+// Example code for writing to the two 8-bit data0/data1 bytes that are
+// a part of the Flash "User-selected words" (aka Option bytes).
+// To reduce the code footpint no timeouts are implemented in the code. It simply
+// waits for the busy-flag to be cleaed. The two wait-loops could be replaced 
+// with a Delay_Ms(10) if speed is not an issue.
+//
+// June 13, 2023 Mats Engstrom (github.com/mengstr)
+//
+
+#define SYSTEM_CORE_CLOCK 48000000
+
+#include "ch32v003fun.h"
+#include <stdio.h>
+void FlashOptionData(uint8_t data0, uint8_t data1) {
+	volatile uint16_t hold[6]; 		// array to hold current values while erasing
+
+	// The entire 64 byte data block of the "User-selected words" will be erased
+	// so we need to keep a copy of the content for re-writing after erase.
+	// Save a few (20) bytes code space by moving 32 bits at a time.
+	// 			hold[0]=OB->RDPR;
+	// 			hold[1]=OB->USER;
+	// 			hold[2]=data0;
+	// 			hold[3]=data1;
+	// 			hold[4]=OB->WRPR0;
+	// 			hold[5]=OB->WRPR1;
+	uint32_t *hold32p=(uint32_t *)hold;
+	uint32_t *ob32p=(uint32_t *)OB_BASE;
+	hold32p[0]=ob32p[0]; 			// Copy RDPR and USER
+	hold32p[1]=data0+(data1<<16);	// Copy in the two Data values to be written
+	hold32p[2]=ob32p[2];			// Copy WRPR0 and WEPR1
+
+	// Unlock both the general Flash and the User-selected words
+	FLASH->KEYR = FLASH_KEY1;
+	FLASH->KEYR = FLASH_KEY2;
+	FLASH->OBKEYR = FLASH_KEY1;
+	FLASH->OBKEYR = FLASH_KEY2;
+
+	FLASH->CTLR |= CR_OPTER_Set;			// OBER RW Perform user-selected word erasure	
+	FLASH->CTLR |= CR_STRT_Set;    			// STRT RW1 Start. Set 1 to start an erase action,hw automatically clears to 0
+	while (FLASH->STATR & FLASH_BUSY);		// Wait for flash operation to be done
+	FLASH->CTLR &= CR_OPTER_Reset; 			// Disable erasure mode	
+
+	// Write the held values back one-by-one
+	FLASH->CTLR |= CR_OPTPG_Set;   			// OBG  RW Perform user-selected word programming
+	uint16_t *ob16p=(uint16_t *)OB_BASE;
+	for (int i=0;i<sizeof(hold)/sizeof(hold[0]); i++) {
+		ob16p[i]=hold[i];
+		while (FLASH->STATR & FLASH_BUSY);	// Wait for flash operation to be done
+	}
+	FLASH->CTLR &= CR_OPTPG_Reset;			// Disable programming mode
+
+	FLASH->CTLR|=CR_LOCK_Set;				// Lock flash memories again
+
+	return;
+}
+
+
+
+//
+//
+//
+int main() {
+	SystemInit48HSI();
+	SetupDebugPrintf();
+	Delay_Ms(250);
+	
+	uint8_t bootcnt=OB->Data0;
+	bootcnt++;
+	FlashOptionData(bootcnt,0);
+	printf("Boot count is %d\n",bootcnt);
+
+	for(;;);
+}