2.0 Circuit Description
CX28394/28395/28398
2.3 System Bus
Quad/x16/Octal—T1/E1/J1 Framers
Note that the online framer's multiframe search status is not directly reported
to the processor, but instead is monitored by examination of transmit error status:
TMERR, TSERR, and TCERR [addr 00B]. If the system incorporates a certain
number of multiframe pattern errors (or a certain error ratio) into the loss of
transmit frame alignment criteria, the processor must count multiframe pattern
errors to determine when to force a transmit reframe [TFORCE; addr 071].
Transmit Frame Alignment
Criteria
The frame synchronization criteria used by the offline framer is set in the
TFRAME[3:0] of the Transmit Framer Configuration register [TCR0; addr 070].
(Tables 3-15 and 3-16 illustrate supported transmit framing formats. Also, see
Tables 3-17 and 3-18, Criteria for Loss/Recovery of Transmit Frame Alignment.)
Transmit/Receive Framer
Arbitration
The offline framer is shared between the RCVR and XMTR and can only
search in one direction at a time. Consequently, the host processor can manually
arbitrate between RCVR and XMTR reframe requests by manipulating the
ABORT and FORCE controls, or by allowing the framer to automatically
arbitrate LOF requests.
The offline framer waits until the current search is complete [FSTAT;
addr 017] before checking for pending LOF reframe requests. If both online
framers have pending reframe requests, the offline framer aligns to the opposite
direction of that 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, framing in the opposite direction
must be masked. If, at the conclusion of a receive search timeout, 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 manually
arbitrate among pending reframe requests by controlling the 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 (ALMI, 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
}
2-38
Conexant
100054E
CONEXANT [ CONEXANT SYSTEMS, INC ]
