diff options
| author | Robert Garbee <robert@gag.com> | 2012-07-18 18:41:00 -0600 |
|---|---|---|
| committer | Robert Garbee <robert@gag.com> | 2012-07-18 18:41:00 -0600 |
| commit | ada6f2dfc045e77cb9499f20cdec1b4a54ef0db1 (patch) | |
| tree | 879f53e8121f71d3c4ac924298b9472dee564abe /src/avr/ao_pwmin.c | |
| parent | e2b472bbb2418fc13be42dbc7c52beb88479c46d (diff) | |
telescience: correctly calculating rate values with higher resolution
Diffstat (limited to 'src/avr/ao_pwmin.c')
| -rw-r--r-- | src/avr/ao_pwmin.c | 28 |
1 files changed, 24 insertions, 4 deletions
diff --git a/src/avr/ao_pwmin.c b/src/avr/ao_pwmin.c index 73a153b2..84397357 100644 --- a/src/avr/ao_pwmin.c +++ b/src/avr/ao_pwmin.c @@ -25,20 +25,40 @@ * project payload developed at Challenger Middle School. */ -volatile __data uint16_t ao_icp3_count; +volatile __data uint16_t ao_icp3_count = 0; +volatile __data uint16_t ao_icp3_last = 0; + +uint16_t ao_icp3(void) +{ + uint16_t v; + ao_arch_critical( + v = ao_icp3_count; + ); + return v; +} static void ao_pwmin_display(void) __reentrant { /* display the most recent value */ - printf("icp 3: %5u\n", ao_icp3_count); + printf("icp 3: %5u\n", ao_icp3()); } + + ISR(TIMER3_CAPT_vect) { + uint8_t lo = ICR3L; uint8_t hi = ICR3H; - ao_icp3_count = (hi <<8) | lo; + uint16_t ao_icp3_this = (hi <<8) | lo; + + /* handling counter rollovers */ + if (ao_icp3_this >= ao_icp3_last) + ao_icp3_count = ao_icp3_this - ao_icp3_last; + else + ao_icp3_count = ao_icp3_this + (65536 - ao_icp3_last); + ao_icp3_last = ao_icp3_this; } __code struct ao_cmds ao_pwmin_cmds[] = { @@ -56,7 +76,7 @@ ao_pwmin_init(void) (0 << ICES3) | /* input capture on falling edge (don't care) */ (0 << WGM33) | /* normal mode, OCR3A */ (0 << WGM32) | /* normal mode, OCR3A */ - (4 << CS30)); /* clk/256 from prescaler */ + (3 << CS30)); /* clk/64 from prescaler */ |