2.0 Circuit Description
CX28394/28395/28398
2.2 Receiver
Quad/x16/Octal—T1/E1/J1 Framers
The offline framer waits until the current search is complete (see [FSTAT;
addr 017]) before checking for pending LOF reframe requests. If both online
framers have pending reframe requests, the offline framer aligns to the direction
opposite from that which was most recently searched. For example, if TLOF is
pending at the conclusion of a receive search which timed out without finding
alignment, the offline framer switches to search in the transmit direction. The
TLOF switchover is prevented in the preceding example if the processor asserts
TABORT to mask the transmit reframe request. TABORT does not affect TLOF
status reporting. For applications that frame in only one direction, the opposite
direction should be masked. If, at the conclusion of a receive search, TLOF status
is asserted but masked by TABORT, the offline framer continues to search in the
receive direction. For applications that frame in both directions, the processor can
allow the offline framer to automatically arbitrate among pending reframe
requests, or may elect to manually control reframe precedence. An example of
manual control follows:
1
2
3
4
5
Initialize RABORT = 1 and TABORT = 1
Enable RLOF and TLOF interrupts
Read clear pending ISR interrupts
Release RABORT = 0
Call LOF Service Routine if either RLOF or TLOF interrupt;
{
(check current LOF status [ALM1, 2; addr 047, 048]
If RLOF recovered and TLOF lost
—Assert RABORT = 1
—Release TABORT = 0
If RLOF lost or TLOF recovered
—Assert TABORT = 1
—Release RABORT = 0
}
The status of the offline framer can be monitored for diagnostic purposes
using the Offline Framer Status register [FSTAT; addr 017]. The register reports
the following: whether the offline framer is looking at the receive or transmit data
streams (RX/TXN); whether the framer is actively searching for a frame
alignment (ACTIVE); whether the framer found multiple framing candidates
(TIMEOUT); whether the framer found frame sync (FOUND); and whether the
framer found no frame alignment candidates (INVALID). Note that these status
bits are updated in real time and might be active for only very short (1-bit) periods
of time. Table 2-1 lists the receive framer modes.
2-14
Conexant
100054E
CONEXANT [ CONEXANT SYSTEMS, INC ]
