__no_init

__no_init 是給編譯器linker使用，爲禁止系統啓動時初始化，是定義在不初始化的區域。可用於硬件復位或看門狗異常復位標記狀態，但是在系統上電覆位時爲不定值。

__no_init unsigned int ram_val1;
__no_init unsigned int ram_val2 @0x20000400;
int main(void)
{
	printf("ram_val1:%d, addr:0x%08x\r\n", ram_val1, (unsigned int *)&ram_val1);
	printf("ram_val2:%d, addr:0x%08x\r\n", ram_val2, (unsigned int *)&ram_val2);
	ram_val1++;
	ram_val2++;
	
	while (1)
	{
	}
	return 0;
}

上面代碼爲一個簡單的程序應用邏輯，ram_val1地址由編譯器分配，ram_val2爲指定地址0x20000400（@爲指定地址）。
軟件復位：

ram_val1:1026533183, addr:0x2001c620
ram_val2:-1862674153, addr:0x20000400
//復位
ram_val1:1026533184, addr:0x2001c620
ram_val2:-1862674152, addr:0x20000400
//復位
ram_val1:1026533185, addr:0x2001c620
ram_val2:-1862674151, addr:0x20000400

上電覆位:

ram_val1:489399103, addr:0x2001c620
ram_val2:-1862543081, addr:0x20000400
//上電覆位
ram_val1:489399167, addr:0x2001c620
ram_val2:-1866868457, addr:0x20000400
//上電覆位
ram_val1:489400127, addr:0x2001c620
ram_val2:-1862674153, addr:0x20000400

系統上電覆位時ram_val1和ram_val2爲不定值，軟件復位可不被系統啓動初始化，維持其值不變。