*/
/**
- * NOTE:
* In slotted CSMA-CA frames must be sent on backoff boundaries (slot width:
- * 320 us). On TelosB the only clock source with sufficient accuracy is the
- * external quartz, unfortunately it is not precise enough (32.768 Hz).
- * Therefore, currently the following code is not even trying to achieve
- * accurate timing.
+ * 320 us). The TelosB platform lacks a clock with sufficient precision and
+ * accuracy, i.e. for slotted CSMA-CA the timing is *not* standard compliant
+ * (this code is experimental)
*/
#include "TKN154_platform.h"
provides interface ReliableWait;
provides interface ReferenceTime;
uses interface TimeCalc;
- uses interface LocalTime<T62500hz>;
+ uses interface GetNow<bool> as CCA;
+ uses interface Alarm<T62500hz,uint32_t> as SymbolAlarm;
+ uses interface Leds;
}
implementation
{
+ enum {
+ S_WAIT_OFF,
+ S_WAIT_RX,
+ S_WAIT_TX,
+ S_WAIT_BACKOFF,
+ };
+ uint8_t m_state = S_WAIT_OFF;
-#define UWAIT1 nop();nop();nop();nop()
-#define UWAIT2 UWAIT1;UWAIT1
-#define UWAIT4 UWAIT2;UWAIT2
-#define UWAIT8 UWAIT4;UWAIT4
-
- async command void CaptureTime.convert(uint16_t time, ieee154_reftime_t *localTime, int16_t offset)
+ async command error_t CaptureTime.convert(uint16_t time, ieee154_timestamp_t *localTime, int16_t offset)
{
// TimerB is used for capturing, it is sourced by ACLK (32768Hz),
- // we now need to convert the capture "time" into ieee154_reftime_t.
+ // we now need to convert the capture "time" into ieee154_timestamp_t.
// With the 32768Hz quartz we don't have enough precision anyway,
// so the code below generates a timestamp that is not accurate
- // (deviating about +-50 microseconds; this could probably
- // improved if we don't go through LocalTime)
uint16_t tbr1, tbr2, delta;
uint32_t now;
atomic {
tbr1 = TBR;
tbr2 = TBR;
} while (tbr1 != tbr2); // majority vote required (see msp430 manual)
- now = call LocalTime.get();
+ now = call SymbolAlarm.getNow();
}
if (time < tbr1)
delta = tbr1 - time;
else
delta = ~(time - tbr1) + 1;
- *localTime = now - delta*2 + offset;
+ *localTime = now - delta * 2 + offset; /* one tick of TimerB ~ two symbols */
+ return SUCCESS;
}
- async command void ReliableWait.busyWait(uint16_t dt)
+ async command bool ReliableWait.ccaOnBackoffBoundary(ieee154_timestamp_t *slot0)
{
- uint32_t start = call LocalTime.get();
- while (!call TimeCalc.hasExpired(start, dt))
- ;
+ // There is no point in trying
+ return (call CCA.getNow() ? 20: 0);
}
- async command void ReliableWait.waitCCA(ieee154_reftime_t *t0, uint16_t dt)
+ async command bool CaptureTime.isValidTimestamp(uint16_t risingSFDTime, uint16_t fallingSFDTime)
{
- while (!call TimeCalc.hasExpired(*t0, dt))
- ;
- signal ReliableWait.waitCCADone();
+ // smallest packet (ACK) takes
+ // length field (1) + MPDU (5) = 6 byte => 12 * 16 us = 192 us
+ return (fallingSFDTime - risingSFDTime) > 5;
}
- async command void ReliableWait.waitTx(ieee154_reftime_t *t0, uint16_t dt)
+ async command void ReliableWait.waitRx(uint32_t t0, uint32_t dt)
{
- while (!call TimeCalc.hasExpired(*t0, dt))
- ;
- signal ReliableWait.waitTxDone();
+ if (m_state != S_WAIT_OFF){
+ ASSERT(0);
+ return;
+ }
+ m_state = S_WAIT_RX;
+ call SymbolAlarm.startAt(t0 - 16, dt); // subtract 12 symbols required for Rx calibration
}
- async command void ReliableWait.waitRx(ieee154_reftime_t *t0, uint16_t dt)
+ async command void ReliableWait.waitTx(ieee154_timestamp_t *t0, uint32_t dt)
+ {
+ if (m_state != S_WAIT_OFF){
+ ASSERT(0);
+ return;
+ }
+ m_state = S_WAIT_TX;
+ call SymbolAlarm.startAt(*t0 - 16, dt); // subtract 12 symbols required for Tx calibration
+ }
+
+ async command void ReliableWait.waitBackoff(uint32_t dt)
{
- while (!call TimeCalc.hasExpired(*t0, dt))
- ;
- signal ReliableWait.waitRxDone();
+ if (m_state != S_WAIT_OFF){
+ ASSERT(0);
+ return;
+ }
+ m_state = S_WAIT_BACKOFF;
+ call SymbolAlarm.start(dt);
}
-
- async command void ReferenceTime.getNow(ieee154_reftime_t* reftime, uint16_t dt)
+
+ async event void SymbolAlarm.fired()
+ {
+ switch (m_state)
+ {
+ case S_WAIT_RX: m_state = S_WAIT_OFF; signal ReliableWait.waitRxDone(); break;
+ case S_WAIT_TX: m_state = S_WAIT_OFF; signal ReliableWait.waitTxDone(); break;
+ case S_WAIT_BACKOFF: m_state = S_WAIT_OFF; signal ReliableWait.waitBackoffDone(); break;
+ default: ASSERT(0); break;
+ }
+ }
+
+ async command void ReferenceTime.getNow(ieee154_timestamp_t* timestamp, uint16_t dt)
{
- *reftime = call LocalTime.get();
+ *timestamp = call SymbolAlarm.getNow() + dt;
}
- async command uint32_t ReferenceTime.toLocalTime(ieee154_reftime_t* refTime)
+ async command uint32_t ReferenceTime.toLocalTime(const ieee154_timestamp_t* timestamp)
{
- return *refTime;
+ return *timestamp;
}
}