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PM73121 Datasheet(PDF) 55 Page - PMC-Sierra, Inc |
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PM73121 Datasheet(HTML) 55 Page - PMC-Sierra, Inc |
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55 / 223 page  PM73121 AAL1gator II PMC-Sierra, Inc. PMC-980620 ,VVXH AAL1 SAR Processor Data Sheet QSPQSD@U6S`Ã6I9Ã8PIAD9@IUD6GÃUPÃQH8TD@SS6ÃDI8Ã6I9ÃAPSÃDUTÃ8VTUPH@ST¶ÃDIU@SI6GÃVT@ sor of 128 (for E1) or 96 (for T1). For these configurations the queues will always be sched- uled in the same frame. Therefore, even if these queues are added at different times they will still be scheduled at the same time. Staggering clocks of the different lines can also help. Since cells are scheduled when a frame completes, staggering lines can offset the frame completion point for the different lines with respect to each other. 3. The actual build time of a cell depends on microprocessor activity and contention with other internal state machines for the AAL1gator II memory bus. Therefore there will be some minor CDV that is added on a per cell basis, based on current microprocessor/memory traffic. This CDV is usually less than 4 µs and is not very noticeable. 4. If there is backpressure on the UTOPIA bus, cells will not be able to be sent which also causes CDV. 3.3 Transmit Adaptation Layer Processor (TALP) 3.3.1 OAM Cell Generation When an OAM cell transmission is requested, it is sent at the first available opportunity. Transmit OAM cells have higher priority than cells scheduled by the CSD circuit. Because of this, care should be taken to ensure that OAM cells do not overwhelm the transmitter to such an extent that data cells are starved of adequate opportunities. The rate of OAM cells must be limited for the AAL1gator II to maintain its maximum CSD data rate. To send an OAM cell, the Supervisory Processor (SP) writes supervisory cells into one of two dedicated cell buffers located in external memory. When the cell is assembled in the buffer, the SP must set the appropriate bit in the command register (refer to section 7.9 “CMDREG (Com- mand Register)” on page 165). The TALP sends the cell as soon as possible, then clears the appropriate attention bit to indicate the requested cell has been sent. If requests for both OAM cells are active at the time the command register is read by the AAL1gator II, OAM cell 0 will always be sent because it is assigned a higher priority. Therefore, to control the order of OAM cell transmission, the SP should set only one OAM attention bit at a time and wait until it is cleared before setting the other attention bit. OAM cells can optionally have the 48-byte OAM payload CRC-10 protected. This is accom- plished by a CRC circuit that monitors the OAM cell as it is sent to the TUTOPIA and computes the CRC on the fly. It then substitutes the 10-bit resultant CRC, preceded by six 0s, for the last two bytes of the cell. |
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