Leonrado获得当前串口速率

最近在研究 Loenrado 的USB，在\arduino-1.8.4\hardware\arduino\avr\cores\arduino\CDC.cpp 中发现有趣的代码：

			// We check DTR state to determine if host port is open (bit 0 of lineState).
			if (1200 == _usbLineInfo.dwDTERate && (_usbLineInfo.lineState & 0x01) == 0)
			{
#if MAGIC_KEY_POS != (RAMEND-1)
				// Backup ram value if its not a newer bootloader.
				// This should avoid memory corruption at least a bit, not fully
				if (magic_key_pos != (RAMEND-1)) {
					*(uint16_t *)(RAMEND-1) = *(uint16_t *)magic_key_pos;
				}
#endif
				// Store boot key
				*(uint16_t *)magic_key_pos = MAGIC_KEY;
				wdt_enable(WDTO_120MS);
			}

 

这段代码是用来实现 Leonrado 刷新的：通过设置当前USB 传输速度为 1200，然后让板子重启进入Bootloader响应刷写指令而无需使用板载的 Reset按钮（未来会做更具体的分析）。
_usbLineInfo.dwDTERate 这里就是当前设定的USB 通讯速度，因此我们在这里添加代码根据当前速度设定LED On Off。加入的代码段如下：

#if MAGIC_KEY_POS != (RAMEND-1)
			// For future boards save the key in the inproblematic RAMEND
			// Which is reserved for the main() return value (which will never return)
			if (_updatedLUFAbootloader) {
				// horray, we got a new bootloader!
				magic_key_pos = (RAMEND-1);
			}
#endif
//LABZ_DEBUG_START
if (300 == _usbLineInfo.dwDTERate && (_usbLineInfo.lineState & 0x01) == 0)
{
        digitalWrite(2,HIGH);
        digitalWrite(3,LOW);
        digitalWrite(4,LOW);
        digitalWrite(5,LOW);
        digitalWrite(6,LOW);
        digitalWrite(7,LOW);
}
if (1200 == _usbLineInfo.dwDTERate && (_usbLineInfo.lineState & 0x01) == 0)
{
        digitalWrite(2,LOW);
        digitalWrite(3,HIGH);
        digitalWrite(4,LOW);
        digitalWrite(5,LOW);
        digitalWrite(6,LOW);
        digitalWrite(7,LOW);
}
if (2400 == _usbLineInfo.dwDTERate && (_usbLineInfo.lineState & 0x01) == 0)
{
        digitalWrite(2,LOW);
        digitalWrite(3,LOW);
        digitalWrite(4,HIGH);
        digitalWrite(5,LOW);
        digitalWrite(6,LOW);
        digitalWrite(7,LOW);
}
if (4800 == _usbLineInfo.dwDTERate && (_usbLineInfo.lineState & 0x01) == 0)
{
        digitalWrite(2,LOW);
        digitalWrite(3,LOW);
        digitalWrite(4,LOW);
        digitalWrite(5,HIGH);
        digitalWrite(6,LOW);
        digitalWrite(7,LOW);
}
if (9600 == _usbLineInfo.dwDTERate && (_usbLineInfo.lineState & 0x01) == 0)
{
        digitalWrite(2,LOW);
        digitalWrite(3,LOW);
        digitalWrite(4,LOW);
        digitalWrite(5,LOW);
        digitalWrite(6,HIGH);
        digitalWrite(7,LOW);
}
if (19200 == _usbLineInfo.dwDTERate && (_usbLineInfo.lineState & 0x01) == 0)
{
        digitalWrite(2,LOW);
        digitalWrite(3,LOW);
        digitalWrite(4,LOW);
        digitalWrite(5,LOW);
        digitalWrite(6,LOW);
        digitalWrite(7,HIGH);
}
//LABZ_DEBUG_ENd
			// We check DTR state to determine if host port is open (bit 0 of lineState).
			if (1200 == _usbLineInfo.dwDTERate && (_usbLineInfo.lineState & 0x01) == 0)
			{
#if MAGIC_KEY_POS != (RAMEND-1)
				// Backup ram value if its not a newer bootloader.
				// This should avoid memory corruption at least a bit, not fully
				if (magic_key_pos != (RAMEND-1)) {
					*(uint16_t *)(RAMEND-1) = *(uint16_t *)magic_key_pos;
				}
#endif
				// Store boot key
				*(uint16_t *)magic_key_pos = MAGIC_KEY;
				wdt_enable(WDTO_120MS);
			}

 

这样，当设定不同速度时， D2-D7 上的LED会分别亮起来。

编写一个简单的 Arduino代码

void setup() {
  // put your setup code here, to run once:
        pinMode(2,OUTPUT);
        pinMode(3,OUTPUT);
        pinMode(4,OUTPUT);
        pinMode(5,OUTPUT);
        pinMode(6,OUTPUT);
        pinMode(7,OUTPUT);

        digitalWrite(2,LOW);
        digitalWrite(3,LOW);
        digitalWrite(4,LOW);
        digitalWrite(5,LOW);
        digitalWrite(6,LOW);
        digitalWrite(7,LOW);
}

void loop() {
  // put your main code here, to run repeatedly:

}

 

比如当前的IDE 的 Serial Monitor 设定为 4800, D5上面的LED会亮