Status And Event Bus; Status Indication; Table 2-15: Signal Values For A Pointer Difference Status; Table 2-16: Signal Values For A Channel Bonding Skew - Xilinx RocketIO X User Manual

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Status and Event Bus

The Virtex-II Pro X design has merged several signals together to provide extra
functionality over the Virtex-II Pro™ design. The signals CHBONDDONE,
RXBUFSTATUS, and RXCLKCORCNT were previously used independently of each other
to indicate status. In the Virtex-II Pro X design, these signals are concatenated together to
provide a status and event bus.
There are two modes of this concatenated bus, status mode and event mode. In status
mode, the bus indicates either the difference between the read and write pointers of the
receive side FIFO or the skew of the last channel bond event.

Status Indication

In status mode, the RXBUFSTATUS and RXCLKCORCNT pins alternate between the
buffer pointer difference and channel bonding skew. The protocol is described by three
sequential clocks (STATUS and DATA are one clock in duration) when operating with a 32-
bit or 40-bit internal data-width, or six sequential clocks (STATUS and DATA are two
clocks in duration) when operating with a 16-bit or 20-bit internal data width:
where
STATUS INDICATOR can indicate either pointer difference or channel bond skew,
DATA0 indicates status data 5:3, and DATA1 indicates status data 2:0.
Table 2-15
pointerDiff[5:0] holds the pointer difference between the receive write and read pointers. If
the pointerDiff[5:0] is < 6'b000110, then RXFIFO is almost under flown. If the
pointerDiff[5:0] is > 6'b111001, then the RXFIFO is almost over flown.

Table 2-15: Signal Values for a Pointer Difference Status

Table 2-16
cbSkew[5:0] holds the pointer difference between the receive write and read pointers:

Table 2-16: Signal Values for a Channel Bonding Skew

68
<STATUS INDICATOR> <DATA0><DATA1>
shows the signal values for a pointer difference status where the variable
Status
STATUS INDICATOR
DATA0
DATA1
shows the signal values for a channel bonding skew where the variable
Status
STATUS INDICATOR
DATA0
DATA1
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Chapter 2: Digital Design Considerations
CHBONDDONE RXBUFSTATUS
1'b0
1'b0
1'b0
CHBONDDONE RXBUFSTATUS
1'b0
1'b0
1'b0
RXCLKCORCNT
2'b01 3'b000
2'b00 pointerDiff[5:3]
2'b00 pointerDiff[2:0]
RXCLKCORCNT
2'b01 3'b001
2'b00 cbSkew[5:3]
2'b00 cbSkew[2:0]
RocketIO™ X Transceiver User Guide
UG035 (v1.5) November 22, 2004