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24 www.xilinx.com SPI-4.2 Lite v4.3 User Guide
UG181 June 27, 2008
Chapter 2: Core Architecture
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SnkFFSOP Output Sink FIFO Start of Packet: When asserted (active high), this signal indicates the start of
a packet is being read out of the Sink FIFO.
SnkFFEOP Output Sink FIFO End of Packet: When asserted (active high), this signal indicates that the end
of a packet is being read out of the Sink FIFO.
SnkFFErr Output Sink FIFO Error: When asserted (active high), this signal indicates that the current
packet is terminated with an EOP abort condition. This signal is only asserted when
SnkFFEOP is asserted.
SnkFFEmpty_n Output Sink FIFO Empty: When asserted (active low), this signal indicates that the Sink FIFO
is empty. No data can be read until this signal is deasserted. This signal is asserted with
the last data word read out of the FIFO.
SnkFFAlmostEmpty_n Output Sink FIFO Almost Empty: When this signal is asserted (active low), it indicates that one
word remains in the FIFO, and you should deassert the read enable signal on the next
clock cycle. The user’s read logic should evaluate the SnkFFEmpty_n signal to verify
that there is no data in the FIFO in case an additional word was simultaneously written
into the FIFO. An example of the behavior of this interface signal is provided with the
SPI-4.2 Lite core in the Design Example (see the pl4_lite_fifo_loopback_read.v/vhd file.)
SnkFFValid Output Sink FIFO Read Valid: When asserted (active high), this signal indicates that the
information on SnkFFData, SnkFFAddr, SnkFFSOP, SnkFFEOP, SnkFFBurstErr,
SnkFFMod, SnkFFErr, SnkFFDIP4Err, and SnkFFPayloadErr is valid.
SnkFFDIP4Err Output Sink FIFO DIP-4 Error: When asserted (active high), this signal indicates that a DIP-4
parity error was detected with the SPI-4.2 control word ending a packet or burst of data.
This signal is asserted at the end of that packet or burst of data.
SnkFFPayloadDIP4 Output Sink FIFO Payload DIP4 Error: When asserted (active high), this signal indicates that a
DIP-4 parity error was detected with the SPI-4.2 control word starting a packet or burst
of data. This signal is asserted at the end of that packet or burst of data.
SnkFFBurstErr Output Sink FIFO Burst Error: When asserted (active high), this signal indicates that the Sink
core has received data that was terminated on a non-credit boundary without an EOP.
SnkFFBurstErr may be used by the user’s logic to indicate missing EOPs, or incorrectly
terminated bursts. In this case the Sink core does not assert SnkFFEOP or SnkFFErr.
SnkFFPayloadErr Output Sink FIFO Payload Error: When asserted (active high), this signal indicates that the
received data was not preceded by a valid payload control word. Since it is not clear
what the packet Address and SOP should be, it is flagged as an error. This is asserted
with each data word coming out of the FIFO, and will remain asserted until a valid
payload control word is followed by data.
SnkAlmostFull_n Output Sink Almost Full: When asserted (active low), this signal indicates that the Sink core is
approaching full (as defined by the parameter SnkAFThresAssert), and that immediate
action should be taken to prevent overflow.
SnkOverflow_n Output Sink Overflow: When asserted (active low), this signal indicates that the Sink core has
overflowed and is in an error condition. Data will be lost if SnkOverflow_n is asserted,
since no data is written into the FIFO when the overflow signal is asserted.
Table 2-3: Sink FIFO Signals (Continued)
Name
Direction
Description