Summary: ECP5 SerDes Out-Of-Band Tx/Rx
This post is a summary of the findings from my look at using the ECP5 SerDes for USB3 LFPS for quick reference of how to use the ECP5 SerDes semi-documented out-of-band I/O features.
Quick summary:
- In addition to using the ECP5's SerDes pins to drive the SerDes; the SerDes Tx/Rx pins can also be used as Low-Data-Rate (LDR) outputs/inputs while the SerDes is in use.
- This is intended to allow transmission/receipt of out-of-band signals in addition to normal SerDes operation; and thus requires a configured SerDes.
Documentation
To use this functionality, add the following to the invocation of the SerDES DCUA block, replacing CHX with your channel number:
| name | type | description |
|---|---|---|
CHX_LDR_RX2CORE_SEL |
parameter | Set this to 1 to enable receiving out-of-band data; works in parallel with normal SerDes operation. |
CHX_LDR_RX2CORE |
output | When CHX_LDR_RX2CORE1_SEL is set, this carries input value from the SerDes Rx input. Captured post differential input, and thus is single-ended. |
CHX_LDR_CORE2TX_SEL |
parameter | Set this to 1 to drive the SerDes Tx output directly; remains in affect until overridden via a SerDes Client Interface register. You most likely want to leave this at 0. |
CHX_FFC_LDR_CORE2TX_EN |
input | When CHX_LDR_CORE2TX_SEL is 0, this controls whether the SerDes Tx output is driven by the SerDes (0) or by the CHX_LDR_CORE2TX signal (1). |
CHX_LDR_CORE2TX |
input | When this is enabled by either CHX_LDR_CORE2TX_SEL or CHX_FFC_LDR_CORE2TX_EN, the value provided to this signal is directly routed to the SerDes Tx output. |
Warning
These descriptions are based on my initial experiments; and should be taken with a grain of salt. :)