Honored ContributorThe Stratix IV GX transceiver documentation mentions 2 blocks in the PCS that seem to perform the same function: the deskew FIFO and the RX phase compensation FIFO .
Could anyone tell me in which cases these FIFOs have to be used or can be bypassed ? What is their difference !?? Thank You for your clarifications.
Honored ContributorThe Deskew FIFO's are only neccesary, and in fact only available in XAUI mode.
A good explenation can be found on page 1-72 of the handbook (vol.2, rev. nov. 2009). Hope that helps...Honored ContributorHi danv,
Indeed, regarding the use of XAUI protocol, handbook p1-72 provides an explanation about the goal of the so called "deskew FIFO" but though I won’t use XAUI protocol in my application, I was simply curious about the difference in these FIFO circuitries. My opinion were that from a hardware point of view, these PCS sub-blocks both perform the same function but with different range (FIFO depth). Further readings told me I was wrong since the clocking schemes of these FIFOs are quiet different. More over, a point that really put me into confusion is that the deskew FIFO in each receiver channel aims to « align » the lanes in a XAUI link just as I’m looking for aligning multiple incoming data streams within a Stratix IV GX for a chip-to-chip synchronous data transfer. The DPA feature of LVDS receivers would have performed this job in a much more simple way than GX transceivers but unfortunately, my data stream rate is 2Gbps (true-LVDS RX limited to 1.6Gbps). So, even if the use of the “multi-purpose”GX transceivers seems to me a bit “luxiourous” and oversized, it is mandatory because of my data rate (which may double in a near future…). You seem to face a similar concern. It sounds like I will have to address soon you some questions in order to demystify all these transceivers (notably about word alignment for instance…) ! Thanks !
