3.0 Registers
CX28394/28395/28398
3.15 Data Link Registers
Quad/x16/Octal—T1/E1/J1 Framers
AUTO_SL
Automatic SL Bit Insertion—RFSLIP error status is encoded into the transmit PRM contents.
Or, the PRM_SL bit value supplied by the processor is sent.
0 = send PRM_SL value in SL bit
1 = send RFSLIP error status in SL bit
SEND_PRM
Immediately Generate and Send PRM—Similar to AUTO_PRM mode, SEND_PRM instructs
the data link transmitter to format and send a Performance Report Message according to ANSI
T1.403-1995. But SEND_PRM executes immediately rather than waiting for ONESEC
interrupt. Thus SEND_PRM gives processor control over PRM transmit timing. This is easier
for the processor to manage if other FDL message types must also be transmitted.
0AB—TDL #1 FIFO Empty Control (TDL1_FEC)
Unused bits are reserved and should be written to 0.
7
6
5
4
3
2
1
0
—
—
FEC[5]
FEC[4]
FEC[3]
FEC[2]
FEC[1]
FEC[0]
FEC[5:0]
Near Empty Transmit FIFO Threshold—Selects FIFO depth of near empty interrupt [TNEAR;
addr 009] and near empty level status [TNEAR1; addr 0AE]. The TNEAR interrupt is
activated when the number of data bytes remaining to be transmitted from the FIFO falls below
the selected threshold. The TNEAR1 indicator is active as long as the number of processor
filled FIFO locations is below the selected threshold. Thus TNEAR1 is active high when the
transmit FIFO is completely empty and remains active until the processor writes the selected
threshold number of bytes to TDL1 [addr 0AD]. Assuming the processor writes 64 bytes to
completely fill an empty FIFO, then a TNEAR interrupt occurs after the transmitter has sent
the number of bytes required to bring the FIFO level back down below the selected threshold.
Hence, the processor can consecutively write 64 - FEC[5:0] number of bytes to the transmit
FIFO in response to a TNEAR interrupt. The interrupt also signifies how much time remains
(in bytes) for the processor to write TDL1 before transmit FIFO is emptied. Typically,
FEC[5:0] is set to a small value (below 10 byte threshold) to minimize the number of TNEAR
interrupts and maximize the time between TNEAR interrupts.
FEC[5:0]
00 0000
00 0001
00 0010
|
Byte threshold @ TNEAR
Disabled
Empty @ TNEAR
Disabled
63 empty
62 empty
|
1 byte threshold
2 byte threshold
|
11 1110
11 1111
62 byte threshold
63 byte threshold
2 empty
1 empty
3-82
Conexant
100054E
CONEXANT [ CONEXANT SYSTEMS, INC ]
