á
PRELIMINARY
DS3 UNI FOR ATM
XRT7245
REV. 1.03
137
It reads in those cells that have identified as “Test
Cells” from the RxFIFO
Acquires and Maintains “PRBS Lock” with the pay-
load data, within these Test Cells.
Reports the occurrences of errors.
4.3.2.1
The Test Cell Receiver will monitor those cells that
reach the RxFIFO, within the Receive UTOPIA Inter-
face block, and, from that “stream of incoming cells”
identify and collect the test cells. The Test Cell
Receiver will use the “user-specified” header byte
patterns, as written into the “Test Cell Header Byte”
registers-1 through 4 (Address = 08h to 0Bh), in order
identify these test cells.
Identifying the Test Cells
4.3.2.2
During Test Cell production, the Test Cell Generator
will fill in the “payload portions” of each test cell with
bytes that were generated by a “Pseudo-Random
Byte Sequence (PRBS) generator. Consequently, the
contents within the cell payload bytes (of these test
cells) do follow a pre-defined sequence.
After the Test Cell Receiver has started to “collect”
these test cells from the RxFIFO, it will “strip off” the
cell header bytes and will begin to evaluate their pay-
load bytes. One of the first things that the Test Cell
Receiver will try to do is to look for this “pre-defined
(PRBS) sequence” within this test cell payload data.
Once the Test Cell Receiver has found this “pre-
defined” sequence within the test cell payload data,
it will inform the user of this fact by asserting the
“PRBS Lock” bit-field, within the “Test Cell Control
and Status” Register; as depicted below.
Acquiring and Maintaining “PRBS Lock”
As long as the Test Cell Receiver has found (and
continues to find) this pre-defined sequence in the
incoming Test Cell payload data, it will keep this
bit-field asserted (e.g., at a logic “1”).
4.3.2.3
Evaluating the Test Cell Payload Data
and Reporting Errors
Once the Test Cell Receiver has acquired “PRBS Lock”
with the contents of the incoming Test Cell payload
data; then it can begin to compare this data with the
“pre-defined” PRBS pattern of data, as produced by
the PRBS Generator (within the Test Cell Generator).
If the Test Cell Receiver detects any discrepancies
between the Test Cell Payload bytes, and the “pre-
defined” PRBS pattern, then it will increment to the
“Test Cell Error Accumulator” Registers. The “Test
Cell Error Accumulator” register actually consists of
two 8-bit “Reset upon Read” registers, as depicted
below.
Test Cell Control and Status Register (Address = 06h)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Unused
Test Cell Enable
Line/System
One Shot Test
One Shot Done
PRBS Lock
R/W
R/W
R/W
R/W
R/W
R/W
RO
RO
1
0
x
x
1
Test Cell Error Accumulator—MSB (Address = 0Ch)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Test Cell Errors—High Byte
RUR
RUR
RUR
RUR
RUR
RUR
RUR
RUR
Test Cell Error Accumulator—LSB (Address = 0Dh)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Test Cell Errors—Low Byte
RUR
RUR
RUR
RUR
RUR
RUR
RUR
RUR