Posted by VIP Experts on May 25, 2016
PCI express Gen 4 implementation is marching towards the Gen 4 0.7 release. It’s important that not only physical layer delivers the 16 GT/s rate, but also the entire protocol stack should be capable of saturating the full allocated bandwidth. To saturate the full bandwidth, following two key features are gaining traction:
In our earlier blog, we discussed about 10-bit extended tag. In this blog, we will discuss about the second feature scaled flow control credits. We will give a brief introduction of the feature to give a jump start to any one ramping up on the latest specifications, and also discuss corresponding verification challenges and solutions.
Current flow control mechanism allows maximum of up to 127 outstanding header credits and 2047 outstanding data credits. The Gen3 x16 link can saturate with these limits in certain scenarios. The flow control mechanism is enhanced with scaled flow control. In scaled flow control mechanism, the maximum outstanding header and data credits can be scaled by a factor of 1, 4 or 16 based on the programmable setting. Note that the credits remain unchanged, one header credit will still be 1 TLP header and one data credit remains to be 16 bytes. Following updates have been done to support scaling flow control: –
Verification of the feature can be divided in 3 categories as described below: –
Synopsys VC VIP for PCIe supports latest specifications and makes it very easy to verify all the new features.
Authors: Anand Shirahatti, Mohd Adil Khan, Jamshed Alum
A global team of protocol experts that share their insights and technical expertise in the areas of Automotive, DRAM and Flash Memories, Storage, Display, MIPI, AMBA, Ethernet, PCIe, USB and many other bus and interface protocols. This comprehensive team participates in standards committees and will provide the latest information and updates as it relates to your future design considerations.