定时器精度和中断会丢失一些微秒吗？

我有一个PIC24F好奇心板-PIC24FJ128GA204-我正试图得到一个准确的第二个时间与tiM1。作为一个源，我使用二次振荡器，它使用一个32678 kHz的XTL。计时器被配置为一个32周期，对应于1毫秒，因此每1 ms调用一个中断，其中MS的计数被存储在主回路中的UTI32 32变量中，我在TMR1OOB.C上忙着等待。ONT变量，当它达到1000时，在UART发送一条消息。在UART的另一面，我有一个应用程序，它读取消息并记录接收到的时间，以及与先前消息的毫秒数的差异。问题是，每个消息都有一个~8ms的累积。22: 5.026 100822: 6.035 100922: 7.045 101022:8.054 100822:9.063 1008怀疑它可能是与UART传输有关的一些东西经常被打断我试图每隔10秒而不是1发送消息。每隔10秒，延时就一直累积到80ms。最后，可能是32个蜱不对应于1毫秒，而是1×x ms，以测试我将周期改变为32768，即1秒。我预期结果大致相同，但它们不是31∶15.216 99 931：16.216 99 931：17.216 1000 31：18.216 99 931：19.216 99 931：20.215 99 931：21.216 1000，看来这个周期影响计时器的准确性。我不明白怎么做。难道每次中断都会丢失一些微秒吗？我在数据表上看不到任何东西，但我找不到任何其他解释。



      以下为原文

    I have a PIC24F Curiosity Board -PIC24FJ128GA204- and I'm trying to get an accurate second timing with the TIM1. As a source I'm using the secondary oscillator, which uses a 32678 kHz xtl.
The timer is configured with a 32 period, which corresponds to 1 ms


void TMR1_Initialize (void)
{
//TMR1 0;
TMR1 = 0x0000;
//Period = 0.001 s; Frequency = 32000 Hz; PR1 32;
PR1 = 0x0020;
//TCKPS 1:1; TON enabled; TSIDL disabled; TCS External; TECS SOSC; TSYNC enabled; TGATE disabled;
T1CON = 0x8006;

IFS0bits.T1IF = false;
IEC0bits.T1IE = true;
tmr1_obj.timerElapsed = false;
}
So, every 1 ms the following interrupt is called, where the count of ms is stored on a uint32_t variable


void __attribute__ ( ( interrupt, no_auto_psv ) ) _T1Interrupt ( )
{
tmr1_obj.count++;
tmr1_obj.timerElapsed = true;
IFS0bits.T1IF = false;
}

In the main loop I do a busy wait on the tmr1_obj.count variable, and when it reaches 1000 a message is sent in UART.

int main(void)
{
// initialize the device
SYSTEM_Initialize();
TMR1_Start();

char msg[] = "Arn";
while (1)
{
// Add your application code
int value = TMR1_SoftwareCounterGet();
if (value == 1000) {
printf("%s", msg);
TMR1_SoftwareCounterClear();
}
}
return -1;
}


On the other side of the UART I have an application that reads the message and logs the time when it was received and the difference in milliseconds with respect to the previous message.
The problem is that I have an accumulation of ~8ms for each message.

22:05.026 1008
22:06.035 1009
22:07.045 1010
22:08.054 1008
22:09.063 1008

Suspecting it could be something related to the UART transmission being often interrupted I tried to send the message every 10 seconds instead of 1. The delay was consistently accumulated to ~80ms each 10 seconds.
Finally, it could be that the 32 ticks do not correspond to 1 ms but to 1.x ms. To test that I changed the period to be 32768, that is, 1 second. I expected the results to be roughly the same, but they weren't

31:15.216 999
31:16.216 999
31:17.216 1000
31:18.216 999
31:19.216 999
31:20.215 999
31:21.216 1000

It seems that the period affects the accuracy of the timer. And I don't understand how. Could it be that for each interruption some microseconds were lost ? I don't see anything on the data sheet, but I can't find any other explanation.