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AR# 16100

LogiCORE SPI-4.2 (POS-PHY L4) v5.0 - Sink Core: The last EOP appears to be stuck in the FIFO

Description

General Description: When packets are received, the last EOP seems to be stuck in the SnkFFDat the bus. SnkFFValid is also de-asserted at this time.

Solution

This issue can occur when SnkFFRdEn_n is de-asserted too early. SnkFFValid is a derivative of SnkFFRdEn_n, and when SnkFFRdEn_n is de-asserted, SnkFFValid will de-assert one clock cycle later.

The data sheet recommends that SnkFFRdEn_n be de-asserted one clock cycle after SnkFFAlmostEmpty_n is asserted. However, SnkFFRdEn_n should be a function of SnkFFAlmostEmpty_n and SnkFFEmpty. The design example that is provided with the v5.0 core (pl4_design_example.pdf) contains an example of this state machine on pages 5 and 6. Please follow the circuit illustrated in this example, which prevents SnkFFRdEn_n from being de-asserted too early.

Future versions of the data sheet will be updated to include this information.

AR# 16100
Date Created 09/03/2007
Last Updated 05/03/2010
Status Archive
Type General Article