188.8.131.52.1. Auto-Speed Negotiation
PIPE Gen3 mode enables ASN between Gen1 (2.5 Gbps), Gen2 (5.0 Gbps), and Gen3 (8.0 Gbps) signaling data rates. The signaling rate switch is accomplished through frequency scaling and configuration of the PMA and PCS blocks using a fixed 32-bit wide PIPE 3.0-based interface.
The PMA switches clocks between Gen1, Gen2, and Gen3 data rates. For a non bonded x1 channel, an ASN module facilitates speed negotiation in that channel. For bonded x2, x4, x8 and x16 channels, the ASN module selects the master channel to control the rate switch. The master channel distributes the speed change request to the other PMA and PCS channels.
The PCIe* Gen3 speed negotiation process is initiated when Hard IP or the FPGA fabric requests a rate change. The ASN then places the PCS in reset, and dynamically shuts down the clock paths to disengage the current active state PCS (either Standard PCS or Gen3 PCS). If a switch to or from Gen3 is requested, the ASN automatically selects the correct PCS clock paths and datapath selection in the multiplexers. The ASN block then sends a request to the PMA block to switch the data rate, and waits for a rate change done signal for confirmation. When the PMA completes the rate change and sends confirmation to the ASN block, the ASN enables the clock paths to engage the new PCS block and releases the PCS reset. Assertion of the pipe_phy_status signal by the ASN block indicates the successful completion of this process.