Analog Devices ADSP-SC58 Series Hardware Reference Manual page 2178

In the example, the sub second increment is 20 (for digital rollover) or 43 (for binary rollover). This addition incre-
ments the EMAC_TM_NSEC
The software must calculate the drift in frequency and update the
The PTP reference clock is the clock at which the system time is updated. When the
NOTE:
EMAC_TM_CTL.TSCFUPDT bit is set to 0, this clock equals the PTP clock. Using fine correction, the
PTP reference clock is generated on the nanoseconds increment signal at which the system time updates.
Target Time Trigger (Alarm)
The PTP module provides an alarm function by triggering an alarm at a preset time. It sets the
EMAC_TM_STMPSTAT.TSTARGT0 bit when the system time matches the value of the
and EMAC_TM_PPS0NTGTM
ule to start or stop PPS output, depending on value programmed in EMAC_TM_PPSCTL.TRGTMODSEL0 bits.
The trigger is enabled by setting EMAC_TM_CTL.TSTRIG bit. Once an alarm has occurred, if the PTP needs an-
other alarm, the software must:
• Clear the status bit
• Reprogram the
EMAC_TM_PPS0TGTM
• Set the EMAC_TM_CTL.TSTRIG bit
If the time programmed in the target time registers has elapsed, then a target time programming error is indicated by
setting the EMAC_TM_STMPSTAT.TSTRGTERR0 bit.
The alarm time is represented in absolute units, not relative units. For example, if the software must generate an
alarm after 10 seconds, it must read the current system time value. Then, the software must add the number corre-
sponding to 10 seconds, and write the result back to the target time registers.
Pulse-Per-Second (PPS)
Pulse-per-second (PPS) is a physical representation of system time. It consists of a single pulse or train of pulses. The
PTP uses PPS for extra synchronization or to monitor the synchronization performance between clocks. With prop-
er configuration, the PTP module can generate PPS signals that are output on the EMAC_PTPPPS[n] pins. The
PTP supports two kinds of PPS output, fixed and flexible.
Fixed Pulse-Per-Second Output
The EMAC supports fixed pulse-per-second (PPS) output that indicates 1-second intervals (default). Change the
frequency of the PPS output by configuring the EMAC_TM_PPSCTL.PPSCTL0 bits. The default value for these
bits is 0000, which configures a 1Hz signal with a pulse width equal to the period of the PTP clock.
The PPS Output Frequencies table shows various PPS output frequencies.
Table 31-46: PPS Output Frequencies
PPSCTL Bit Setting
0001
ADSP-SC58x/ADSP-2158x SHARC+ Processor Hardware Reference
register by 20 ns (1/50 MHz).
registers. This trigger can generate an interrupt and command the flexible PPS mod-
and
EMAC_TM_PPS0NTGTM
Binary Rollover
2 Hz
EMAC Precision Time Protocol (PTP) Engine
EMAC_TM_ADDEND register accordingly.
registers to a future value, and
Digital Rollover
1 Hz
EMAC_TM_PPS0TGTM
31–87