BCM5722 Programmer’s Guide
10/15/07
Broadcom Corporation
Page 19 Transmit Data Path Document 5722-PG101-R
Internal Block Diagram
Figure 6: ISO SBD Internal Block Diagram
ISO SDI
The ISO SDI block implements a 32-bit network time clock that counts in ns. The counter runs off of the 25-MHz core clock
and increments by 40 each clock cycle.
A 16-bit launch time field is defined in the ISO SBD, as shown in Table 6.
The isochronous packet launch time field is added to the upper 16 bits at offset 0xC in the ISO Send Buffer Descriptor (ISO
SBD):
ISO SDI
Data SDI
RDMA
Network Clock
TXMAC
ISO SBD non-empty
Data SBD non-empty
RXMAC
Time Sync Packet Received
Network clock > launch time
SDI = Send Data Initiator
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