PM5381-BI PMC-Sierra, Inc., PM5381-BI Datasheet - Page 530

• Manufacturer Part Number: PM5381-BI
• Description: ATM UNI, Single Channel ATM PHY Interface for 2488.32Mbps
• Manufacturer: PMC-Sierra, Inc.

Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-2000489, Issue 4
Explanation:
The DTPA is late by five clocks and the link layer device takes s number of clocks after DTPA to
stop transfer, resulting in 5 + s words that can be written after the threshold gets exceeded.
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the '1' is to deal with the worst case where the threshold gets exceeded during the write of the
final word of a packet whose size is one block greater than a multiple of 4 (eg. the EOP word
of a 13 word packet, as this word wastes a whole block by itself).
num_min_pack is the number of full minimum-sized packets that can be written during the 5
+ s - 1 clocks. ( The subtraction of 1 refers to the EOP word corresponding to point i)
eg. if s = 2, m = 5, ovrhd_cycles = 0,
num_min_pack = downround( ( 5+2-1) / (5+0) ) = 1.
That is, in those 6 clocks, there could be one full min-size packet that can be written
min_pack_size_in_blocks is the number of blocks occupied by a minimum-sized packet.
eg. if m = 5 clocks cycles, then min_pack_size_in_blocks is 2.
remainder refers to how many blocks of a partial packet gets written after the minimum-sized
packets had been written. (5 + s – 1)mod m is a calculation of how many words are
contained in the final partial packet. The number of blocks occupied is simply that value
divided by 4 rounded up.
the '-1' at the end of the equation refers to the fact that BT in the TXSDQ is one less than
what's required.
Let ovrhd_cycles = number of non-packet payload cycles per transfer
num_min_pack = downround ( ( 5 + s - 1) / (m + ovrhd_cycles) )
min_pack_size_in_blocks = upround ( m / 4 )
remainder = upround ( (( 5 + s - 1) mod m) / 4 )
(each guaranteed null cycle introduced by the
upstream device counts as 1)
S/UNI-2488 Telecom Standard Product Datasheet
Released
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