打印机可能会开机时候在LCD显示屏上显示External SPI flash XFLASH is not responding错误。 该错误一个最直观的影响就是Blet test操作是无法显示数值的，一直显示0. 源码文件Marlin_main.cpp 1052行 1093行 1331行均是相关代码

static void xflash_err_msg()
{
	lcd_clear();
	lcd_puts_P(_n("External SPI flash\nXFLASH is not res-\nponding. Language\nswitch unavailable."));
}

// "Setup" function is called by the Arduino framework on startup.
// Before startup, the Timers-functions (PWM)/Analog RW and HardwareSerial provided by the Arduino-code 
// are initialized by the main() routine provided by the Arduino framework.
void setup()
{
	timer2_init(); // enables functional millis

	mmu_init();

	ultralcd_init();

	spi_init();

	lcd_splash();
    Sound_Init();                                // also guarantee "SET_OUTPUT(BEEPER)"

	selectedSerialPort = eeprom_read_byte((uint8_t *)EEPROM_SECOND_SERIAL_ACTIVE);
	if (selectedSerialPort == 0xFF) selectedSerialPort = 0;
	eeprom_update_byte((uint8_t *)EEPROM_SECOND_SERIAL_ACTIVE, selectedSerialPort);
	MYSERIAL.begin(BAUDRATE);
	fdev_setup_stream(uartout, uart_putchar, NULL, _FDEV_SETUP_WRITE); //setup uart out stream
	stdout = uartout;

#ifdef XFLASH
    bool xflash_success = xflash_init();
	uint8_t optiboot_status = 1;
	if (xflash_success)
	{
		optiboot_status = optiboot_xflash_enter();
#if (LANG_MODE != 0) //secondary language support
        update_sec_lang_from_external_flash();
#endif //(LANG_MODE != 0)
	}
	else
	{
	    xflash_err_msg();
	}
#else
	const bool xflash_success = true;
#endif //XFLASH

通过查看源码，发现该错误信息是Arduino的Setup函数初始化中显示的。是否error是又xflash_init()函数返回的数据决定。

我们在xflash.c的51行找到该函数。他初始化XFLASH_PIN_CS引脚为SPI的CS引脚，然后执行xflash_mfrid_devid()函数判断返回。

int xflash_mfrid_devid(void);


int8_t xflash_init(void)
{
	_CS_HIGH();
	SET_OUTPUT(XFLASH_PIN_CS);
	XFLASH_SPI_ENTER();
	if (!xflash_mfrid_devid()) return 0;
	return 1;
}

xflash_mfrid_devid()函数在xflash.c的193行，主要还是与Flash进行通信，获取Flash的型号。以此来确认是否通信成功。

int xflash_mfrid_devid(void)
{
	_CS_LOW();
	_SPI_TX(_CMD_MFRID_DEVID);           // send command 0x90
	uint8_t cnt = 3;                     // 3 address bytes
	while (cnt--)                        // send address bytes
		_SPI_TX(0x00);
	uint8_t xflash_mfrid = _SPI_RX();  // receive mfrid
	uint8_t xflash_devid = _SPI_RX();  // receive devid
	_CS_HIGH();
	return
		((xflash_mfrid == _MFRID_W25X20CL) && (xflash_devid == _DEVID_W25X20CL)) ||
		((xflash_mfrid == _MFRID_GD25Q20C) && (xflash_devid == _DEVID_GD25Q20C));
}