Hello everybody,
I'm working with tinyos 2.x on an IRIS platform. I need to wait for or
set an alarm to 140 microseconds to get an energy detection value from
the RF230 radio chip. As far as I understand TEP102 and some
correspondence on this newsgroup
(http://www.mail-archive.com/[email protected]/msg30161.html),
the atm128 on the IRIS mote by default is configured to expose its
hardware timers 1 and 3 as "near microsecond" timers, using an external
crystal running at 7.372800 MHz with a prescaler of 8 (resulting in
921600 Hz). Thus I suppose I could configure start BusyWaitMicroC or
AlarmMicro32C with a value of 140 * 0.9216 = 130 to wait at least 140
microseconds. Please point out if my reasoning here is incorrect here at
some point.
Now I also found the MeasureClockC component implementing the
Atm128Calibrate interface that as far as I understand should help me to
do exactly that conversion from/to microseconds from/to units I have to
use with components like LocalTimeMicroC, AlarmMicro32C etc. that are
parametrized with TMicro precision tag and using counters from hardware
timers 1 or 3. However:
Atm128Calibrate.calibrateMicro(140) yields a quite surprising value of
241 (instead of about 130)
Trying with values from 0 to 2000 in steps of 100 yields the following
output with the tinyos printf tool (code used at the end)
i / Atm128Calibrate.calibrateMicro(i) /
Atm128Calibrate.actualMicro(Atm128Calibrate.calibrateMicro(i))
0 112 242
100 204 342
200 296 442
300 389 543
400 481 643
500 573 742
600 665 842
700 757 942
800 850 1043
900 942 1143
1000 1034 1242
1100 1126 1342
1200 1219 1443
1300 1311 1543
1400 1403 1642
1500 1495 1742
1600 1587 1842
1700 1680 1943
1800 1772 2043
1900 1864 2142
2000 1956 2242
To me this seems to be quite far off everything I would expect, or am I
terribly misstaken about something here? I thought this conversion
function would have to be rather linear with a factor of about 0.9126 or
1/0.9126 respectively? Thanks for any clarification on that topic.
Kind Regards,
Andreas
Code used to produce the output:
//module TimerTestC
#include "printf.h"
module TimerTestC {
uses {
interface Boot;
interface Atm128Calibrate as Calibrate;
interface Timer<TMilli> as Timer;
}
}
implementation {
uint32_t i = 0;
uint32_t micro;
uint32_t calibratedUnits;
uint32_t microFromCalibratedUnits;
event void Boot.booted() {
call Timer.startPeriodic(20);
}
event void Timer.fired() {
micro = i;
calibratedUnits = call Calibrate.calibrateMicro(micro);
microFromCalibratedUnits = call
Calibrate.actualMicro(calibratedUnits);
printf(" %5ld %5ld %5ld\n", micro, calibratedUnits,
microFromCalibratedUnits);
printfflush();
i += 100;
if (i > 2000) {
call Timer.stop();
}
}
}
// configuration TimerTestAppC
#include "printf.h"
configuration TimerTestAppC{
}
implementation {
components TimerTestC as TimerTestApp;
components MainC;
components MeasureClockC;
components new TimerMilliC() as Timer;
TimerTestApp.Boot -> MainC;
TimerTestApp.Calibrate -> MeasureClockC;
TimerTestApp.Timer -> Timer;
}
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