px1011a NXP Semiconductors, px1011a Datasheet - Page 14

• Manufacturer Part Number: px1011a
• Description: Px1011a/px1012a Pci Express Stand-alone X1 Phy
• Manufacturer: NXP Semiconductors

Philips Semiconductors
PX1011A_PX1012A_2
Product data sheet
8.9 Clock tolerance compensation
Table 14
Table 14.
The PHY receiver contains an elastic buffer used to compensate for differences in
frequencies between bit rates at the two ends of a link. The elastic buffer is capable of
holding at least seven symbols to handle worst case differences (600 ppm) in frequency
and worst case intervals between SKP ordered-sets. The PHY is responsible for inserting
or removing SKP symbols in the received data stream to avoid elastic buffer overflow or
underflow. The PHY monitors the receive data stream, and when a Skip ordered-set is
received, the PHY can add or remove one SKP symbol from each SKP ordered-set as
appropriate to manage its elastic buffer. Whenever a SKP symbol is added or removed,
the PHY will signal this to the MAC using the RXSTATUS signals. These signals have a
non-zero value for one clock cycle and indicate whether a SKP symbol was added or
removed from the received SKP ordered-set. RXSTATUS should be asserted during the
clock cycle when the COM symbol of the SKP ordered-set is moved across the parallel
interface. If the removal of a SKP symbol causes no SKP symbols to be transferred across
the parallel interface, then RXSTATUS is asserted at the same time that the COM symbol
(that was part of the received skip ordered-set) is transmitted across the parallel interface.
Figure 9
Figure 10
ordered-set.
PWRDWN[1:0]
P0: 00b
P0s: 01b
P1: 10b
Fig 9. Clock correction - insert a SKP
RXSTATUS2,
RXSTATUS1,
RXSTATUS0
RXDATA[7:0]
shows a sequence where the PHY inserted a SKP symbol in the data stream.
RXVALID
summarizes the function of some PXPIPE control signals.
shows a sequence where the PHY removed a SKP symbol from a SKP
RXCLK
Control signals function summary
RXDET_LOOPB
0
0
1
1
X
X
0
1
active
000b
Rev. 02 — 18 May 2006
COM
001b
TXIDLE
0
1
0
1
0
1
0
1
1
000b
SKP
PX1011A/PX1012A
Function description
normal operation
transmitter in idle
loopback mode
illegal
illegal
transmitter in idle
illegal
transmitter in idle
receiver detect
PCI Express stand-alone X1 PHY
SKP
© Koninklijke Philips Electronics N.V. 2006. All rights reserved.
active
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