定时器每 4ms 产生一次溢出
在atmega2560（STK600板）上，我使用Timer0，它是8位定时器。我想每 4 毫秒生成一次溢出...如何将计时器设置为 4 毫秒？ （时钟速度是8MHz，我知道通过潜水（时钟速度）/（预分频器）来设置定时器，当计数器重置时，它会产生溢出中断。但不确定是否设置为4ms！
其次，一旦定时器溢出并生成 OVERFlOW 中断，计算 1 秒..如何做到这一点？
提前致谢！
On atmega2560 (STK600 board), I am using Timer0 which is 8-bit timer. I want to generate an overflow every 4ms...how do I set the timer for 4ms? (the clock speed is 8MHz, I am aware of setting up a timer by diving (clock speed)/(prescaler) and when the counter resets, it generates an overflow interrupt. But not sure about setting for 4ms!
Secondly, once the timer overflows and generates an OVERFlOW interrupt, calculate 1 second..How to do that?
Thanks in advance!
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OVERFLOW 中断不可能达到 4ms：
F_CPU = 8,000,000hz
F_OVERFLOW = 1/0.004s = 250hz
CYCLES_PER_OVERFLOW = F_CPU / F_OVERFLOW = 32,000，即：每 32,000 个 CPU 时钟周期应发生一次溢出
CYCLES_PER_TIMER_TICK = 32,000 / 256 = 125 = 预分频器值
125 不可用作预分频器，但如果该值足够接近您的目的 (4.096ms)，您可以使用 128。
如果没有，可以考虑使用定时器比较中断来代替溢出int。 - 或者更改 F_CPU...
一旦每 4ms 发生一次中断，您可以在每次中断时递增一个全局变量，每次该变量的值达到 250 时，又过去了一秒，该变量可以重新设置为 0 以计入下一秒。
4ms won't be possible with the OVERFLOW interrupt:
F_CPU = 8,000,000hz
F_OVERFLOW = 1/0.004s = 250hz
CYCLES_PER_OVERFLOW = F_CPU / F_OVERFLOW = 32,000, i.e.: An overflow should occur each 32,000 CPU clock cycles
CYCLES_PER_TIMER_TICK = 32,000 / 256 = 125 = prescaler value
125 is not available as prescaler, but you can use 128 if that's close enough for your purpose (4.096ms).
If not, you can consider to use a timer compare interrupt instead of the overflow int. - Or change F_CPU...
Once you have your interrupt each 4ms, you can increment a global variable on each interrupt and each time the variable's value reaches 250, another second has passed and the variable can be re-set to 0 to count towards the next second.