CAN BUS Shield DFR0370 performance

Hi,
I'm using arduino uno and DFR0370 to log CAN Bus.
To measure the DFR0370 performance, I sent CAN message with short period time.
Receive mode was interrupt.
From 10msec to 2msec, it works well. No missing any message.
But, after send CAN message with 1msec period, it cannot receive continuously.
I measured buffer reading time by using "micros()", it was about 1.7msec.
Modifying SPI clock divider to 2 is little bit better, buffer reading time was 1.5msec
I would like to measure every CAN messages without missing.
Below is my full code. Please, give me your hand.

('', '
#include <SPI.h>
#include "df_can.h"

const int SPI_CS_PIN = 10;
MCPCAN CAN(SPI_CS_PIN); // Set CS pin

unsigned char len = 0;
unsigned char buf[8];
char str[20];
int msgID = 0;
unsigned long time[255];
unsigned int timeindex = 0;
String sendmsg;
unsigned int testtimer[2];

void setup()
{
String reportString = "Time\tID\tLn\tD0\tD1\tD2\tD3\tD4\tD5\tD6\tD7";
Serial.begin(250000);
int count = 50; // the max numbers of initializint the CAN-BUS, if initialize failed first!.
do {
CAN.init(); //must initialize the Can interface here!
if(CAN_OK == CAN.begin(CAN_500KBPS)) // init can bus : baudrate = 500k
{
Serial.println("DFROBOT's CAN BUS Shield init ok!");
break;
}
else
{
Serial.println("DFROBOT's CAN BUS Shield init fail");
Serial.println("Please Init CAN BUS Shield again");
delay(100);
if (count <= 1)
Serial.println("Please give up trying!, trying is useless!");
}
}while(count--);
//Serial.println(reportString);
//SPI.setClockDivider(SPI_CLOCK_DIV2);
attachInterrupt(0, MCP2515_ISR, FALLING); // start interrupt
}

void MCP2515_ISR()
{
time[timeindex] = micros();
if(timeindex==255)
{
timeindex=255;
}
else
{
timeindex++;
}
}

void loop()
{
if(timeindex > 0)
{ // check if get data
testtimer[0]=micros();
// iterate over all pending messages
// If either the bus is saturated or the MCU is busy,
// both RX buffers may be in use and after having read a single
// message, MCU does clear the corresponding IRQ conditon.
while (CAN_MSGAVAIL == CAN.checkReceive())
{
// read data, len: data length, buf: data buf
CAN.readMsgBuf(&len, buf);
sendmsg=String(time[timeindex-1])+"\t"+String(CAN.getCanId(),HEX)+"\t"+String(len)+"\t";
// print the data
for(int i = 0; i<len; i++)
{
sendmsg+=String(buf[i],HEX)+"\t";
}
//Serial.println(sendmsg);
//for(int i=0;i<timeindex;i++)Serial.print(String(time[i])+"/");
//Serial.print(String(timeindex)+"/");
}
timeindex--; // clear flag
time[timeindex]=0;
testtimer[1]=micros();
Serial.println(String(testtimer[1]-testtimer[0]));
}
else
{
}
}
[/code]')