[nickdigger]

Originally Posted by t vago

Also, to optimize calculations involving timer2_overflow_count, I decided to have the timer2 overflow handler bump timer2_overflow_count by 256 instead of by 1. That got rid of constantly having to multiply timer2_overflow_count by 256 whenever it was desired to read the time. Also, function delay2() now "calls" the overflow timer to do its delays, but also I'm thinking to get rid of that, in favor of having timer2 drive the LCD output directly by using an output buffer.

injOpenStop = timer2_overflow_count + TCNT2;
if (TIFR2 & (1 << TOV2)) injOpenStop = timer2_overflow_count + 256 + TCNT2;

That above is a slightly modified version that actually manages to save about 18 bytes or so in compilation. Who knew that logical OR-ing would take up more space than just adding? Heh.

The OR was probably (stupidly) ORing 0x00 to each of the 3 high bytes as well. I've been using unions, as below, to eliminate some of that nonsense. With the add-256 method, the compiler knew the high bytes would just carry-the-one from the lower add, hence the "better" compile.
Here's how I optimized my microseconds():

typedef union { ulong  ul;
                struct {uint i0; uint i1;};
                struct {byte b0; byte b1; byte b2; byte b3;}; } union32;

ulong microSeconds (void)
{
  union32 tmp;
  const byte *t2ocptr = (byte *)&timer2_overflow_count;

  cli();
  //tmp.ul = timer2_overflow_count<<8;
  //tmp_tcnt2 = TCNT2;
  tmp.b3 = *(t2ocptr+2);
  tmp.b2 = *(t2ocptr+1);
  tmp.b1 = *(t2ocptr);
  tmp.b0 = TCNT2;
  sei();
  //return (tmp + tmp_tcnt2) * 4;
  return tmp.ul * 4;

//each TCNT2 == 4us
//each timer2_overflow == 1024us == 256us*4
//return (timer2_overflow*256*4 + TCNT2*4)
//ie, return (timer2_overflow*256 + TCNT2) * 4

It's pretty tight. Only 38 bytes compiled, no stack usage, and only 5 instructions between cli & sei. Now that I look at it, 14 of those 38 are the mult-by-4 op.

The timer2 overflow has been vastly expanded, to get rid of microseconds() altogether. The main loop uses timer2 to do its loop delays now, instead of having to track the time by itself. I'm thinking that this may have gotten rid of that freeze-up bug altogether.

I didn't know others were freezing as well. My "blank" screen after the 7min timeout now displays a running clock, and the timer_overflow values. Hopefully this will help me catch the bug in the act.