RX Interface Width Configuration

Versal ACAP GTM Transceivers Architecture Manual (AM017)
Document ID
AM017
Release Date
2022-04-27
Revision
1.0 English

The GTM receiver contains an 80-bit internal datapath in NRZ mode and a 160-bit internal datapath for PAM4 mode that is configurable by setting the RX_PMA_DATA_WIDTH attribute. The interface width is configurable by setting the RX_DATA_WIDTH attribute. In NRZ mode, the interface can be configured to 32, 40, 64, 80, 128, 160, and 256 bits. In PAM4 mode, the interface can be configured to 64, 80, 128, 160, 256, 320, and 512 bits.

The following table shows how the interface width for the RX datapath is selected.

Table 1. RX Interface Datapath Configuration
Encoding Density RX_PMA_DATA_WIDTH Encoding RX_DATA_WIDTH Encoding RX Internal Width RX Interface Width
NRZ Full 0 4 80 32
5 40
6 64
7 80
8 128
9 160
10 256
PAM4 Full 1 6 160 64
7 80
8 128
9 160
10 256
Half 11 320
12 512

When the interface width is configured to either 320 or 512 bits, this results in a half density configuration in which two channel interfaces are combined to act as one. In this mode, only a single PCS/PMA front end channel is in operation. An additional limitation is that the half density configuration must use either the channel 0/1 pair or channel 2/3 pair in the same Quad. Mixing and matching with different channels is not allowed.

When either channel CH0 or CH1 is operating in half density mode, the fabric interface combines the data from adjacent channels to group as a set of 512 bits before forwarding to the RX FIFO. Designating a channel to be used in half density mode can be done by setting the adjacent channel's RX_USRCLK_SEL attribute High. The following table shows possible channel combinations.
Table 2. RX Half Density Modes
CH0 RX_USRCLK_SEL CH1 RX_USRCLK_SEL Fabric Interface Operating Mode
0 0 Both channels are in full density mode.
0 1 CH0 is in half density mode.
1 0 CH1 is in half density mode.
1 1 Invalid.