PRJ - CAN Receiver

#include <SPI.h>
#include "mcp2515_can.h"
const int SPI_CS_PIN = 10;
const int CAN_INT_PIN = 2;   // interrupt pin
mcp2515_can CAN(SPI_CS_PIN); // Set CS pin
unsigned char flagRecv = 0;
unsigned char len = 0;
unsigned char buf[8];
char str[20];
void setup() {
   Serial.begin(115200);
   while (!Serial) {
      ; // wait for serial port to connect. Needed for native USB port only
   }
   
   // start interrupt
   attachInterrupt(digitalPinToInterrupt(CAN_INT_PIN), MCP2515_ISR, FALLING);
    // 注意: 哪些 PIN 才能使用 Interrupt 呢？有没有限制？
   
   // init can bus : baudrate = 500k
   while (CAN_OK != CAN.begin(CAN_500KBPS)) {
      Serial.println("CAN init fail, retry...");
      delay(100);
   }
   Serial.println("CAN init ok!");
}

void MCP2515_ISR() {
   flagRecv = 1;    // 设置一个标志，表示有数据要读取
}

void loop() {                       
   if (flagRecv) {
      // check if get data
      flagRecv = 0; // clear flag
       // 会不会被再次中断，消息就丢失了?
       
      
      Serial.println("into loop");
      
      // iterate over all pending messages
      // If either the bus is saturated or the MCU is busy,
      // both RX buffers may be in use and reading a single
      // message does not clear the IRQ conditon.
      while (CAN_MSGAVAIL == CAN.checkReceive()) {
          // 检测等待被读取的消息
         // todo: CAN_MSGAVAIL 等常量的值是多少？
         Serial.println("checkReceive"); 
         CAN.readMsgBuf(&len, buf);  // 为什么一个简单的 len 要用传地址的方法？
         
         // print the data
         for (int i = 0; i < len; i++) {
            Serial.print(buf[i]); Serial.print("\t");
         }
         Serial.println();
      }
   }
}