VSC6134
Datasheet
7.2.2
GCC Monitor and Generator Using the MPU Interface and
Auto-Incrementation
Description: For both the generator and monitor G.709 blocks, VSC6134 buffers the GCC bytes
between the serial stream and the microprocessor. To speed up data access, the read/write pointer
automatically increments. This feature has been unreliable when incrementing, and therefore resulting
in data corruption either through overwriting data or reading the same data twice.
Workaround: In fail mode, the pointer value does not increment. Therefore, prior to reading or writing
data in the GCC buffer, read back the pointer value, GCC_MPNT to ensure that it is properly set. Even
in the case where a new pointer value was just written, the pointer value should always be read back.
7.2.3
SM/PM/TCM TTI Monitor and Generator Using the Microprocessor
Interface
Description: When accessing data from either the G.709 generator or monitor’s TTI bytes, two issues
may arise. Microprocessor read operations may be preempted from fetching the data if the core is
actively fetching data for transmission in the next frame. This may result in data being present and valid
on the bus a few clock cycles later than expected. Furthermore, the auto-increment feature has been
unreliable in incrementing and therefore resulting in data corruption either through overwriting data or
reading the same data twice.
Workaround: In fail mode, the pointer value does not increment. Therefore, prior to reading or writing
data in the TTI buffer, read back the pointer value, SM/PM/TCM_TTIPNT to ensure that it is properly
set. Even in the case where a new pointer value was just written, the pointer value should always be read
back.
7.2.4
Incoming Alignment Error (IAE) Interrupts
Description: IAE interrupt is set after receiving IAE bits over three consecutive frames. It is not
compliant with the ITU-T G.798 standard, which says should be five.
Workaround: You must provide external logic to make use of the Overhead Extraction Ports on the
VSC6134. Upon detecting IAE alarm from the external logic (likely in an FPGA), the VSC6134 must
send BIAE in the transmit direction. This can be done by disabling automatic BIAE generation
(SM_BIAEAUTO = 0 and TCM_BIAEAUTO = 0) and forcing BIAE generation (SM_BIAEMANU=1
and/or TCM_BIAEMANU = 1).
7.2.5
Framed PRBS Error Counter
Description: During operation when the device is monitoring a G.709 frame with a PRBS payload, the
PRBS payload error counter, FPRBSERRCNT[31:0], has been observed to be unreliable and it may
contain a value larger than actual.
Workaround: You should use the counter value as a qualitative measurement of the system. The
counter value along with the error interrupt and the G.709 overhead BIP counters should be used to
understand the link’s performance.
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VMDS-10185 Revision 4.0
July 2006
VITESSE [ VITESSE SEMICONDUCTOR CORPORATION ]
