VSC7440 datasheet(302/444 Pages) MICROSEMI

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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

285

3.29.3

Detecting Calculation Issues

A sticky bit per port informs if frames are received with the reserved bytes field non-zero. This can be

used to detect if incoming frames contain unexpected information in the reserved bytes field.

If the correction field is outside the valid range –247 to 247–1, another sticky bit is set in the port module

indicating the overflow. The port module replaces in this case the final CF with the overflow indication

value 247–1. This detection is however disabled when using ADDS48 mode because the correction field

in this mode rolls over regularly.

3.29.4

Two-Step Functions

The two-step PTP mode uses software as a middle stage for informing next hubs about residence times.

A FIFO of time stamping events is available for software where ingress and egress time stamps as well

as port numbers can be read out. The FIFO can contain 1,024 time stamp entries.

Figure 85 •

Time Stamp Bus and FIFO

The bus passes through all port modules and terminates in a timestamp FIFO in the rewriter. If the

analyzer has decided to do a two-step operation, the rewriter pushes two entries into the FIFO. The first

entry contains the egress time stamp and the egress port number; the second entry contains the ingress

time stamp and the ingress port number. In addition, a flag indicates whether the entry contains ingress

or egress information.

When correlating frames copied to the CPU with entries in the FIFO, the ingress time stamp found in the

IFH is the same as ingress time stamp found in the FIFO.

Note that the IDLY and EDLY values are not added to the CF field in the two-step case, as the frames are

transferred untouched. Software must manually add these delays for the follow-up frames.

3.29.5

Time of Day Time Stamping

When sending out SYNC frames with full TOD, the rewriter does the TOD time stamping at the time

where the frame passes through the rewriter and the port module is instructed to do a one-step update in

ADDS44

CF += (NSX44@rew)

CF += (CF_org(46)/=NSX48(44))?244:0

CF(46) = CF(47)

CF –= NSX44 CF(46) = NSX48(44)

ADDS48

CF += NSX48

CF –= NSX48

MONITOR

CF –= (NSF – IFH.TSTAMP)

DISABLED

NOP

Table 215 •

Rewriter Operations for One-Step Operation (continued)

Mode

Receiving From

Transmitting To

REW

DEV_0

DEV_1

DEV_n

Tx=1

Egress

PortNo

Egress

Timestamp

TS FIFO

Tx=0

Ingress

PortNo

Ingress

Timestamp

To S/W

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