R

Chapter 2: Core Architecture

Table 2-3:Sink FIFO Signals (Continued)

Name

Direction

Description

 

 

 

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.

 

 

 

24

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SPI-4.2 Lite v4.3 User Guide

 

 

UG181 June 27, 2008

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UG181 specifications

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