Visible to Intel only — GUID: olf1486507543145
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Visible to Intel only — GUID: olf1486507543145
Ixiasoft
6.12.3. Enabling and Disabling Loopback Modes Using Direct Reconfiguration Flow
Cyclone® 10 GX devices have three loopback modes:
- Serial Loopback
- Reverse Serial Loopback (Pre-CDR)
- Reverse Serial Loopback (Post-CDR)
The loopback mode can be dynamically reconfigured by accessing the register space.
Serial Loopback Mode
In serial loopback mode, a path exists between the serializer of the transmitter and the CDR of the receiver, so that the data from the CDR is recovered from the serializer while the data from the receiver serial input pin is ignored. You can enable or disable this mode.
To enable serial loopback mode:
- Perform the necessary steps from steps 1 to 7 in Steps to Perform Dynamic Reconfiguration.
- Perform a read-modify-write to address 0x2E1 to set bit 0 to 1’b1
- Perform the necessary steps from steps 9 to 12 in Steps to Perform Dynamic Reconfiguration.
To disable serial loopback mode:
- Perform the necessary steps from steps 1 to 7 in Steps to Perform Dynamic Reconfiguration.
- Perform a read-modify-write to address 0x2E1 to set bit 0 to 1’b0
- Perform the necessary steps from steps 9 to 12 in Steps to Perform Dynamic Reconfiguration.
You can also enable the serial loopback mode by turning on Enable rx_seriallpbken port in the Native PHY IP Parameter Editor and driving the port to 1’b1.
Reverse Serial Loopback Mode (Pre-CDR)
In the pre-CDR mode, data received through the RX input buffer is looped back to the TX output buffer. You can enable the reverse serial loopback mode by performing read-modify-write to the following registers.
Address | Bit Values |
---|---|
0x137[7] | 1’b1 |
0x13C[7] | 1’b0 |
0x132[5:4] | 2’b00 |
0x142[4] | 1’b1 |
0x11D[0] | 1’b1 |
Reverse Serial Loopback Mode (Post-CDR)
In the post-CDR mode, received data passes through the RX CDR and then loops back to the TX output buffer. Perform read-modify-write to the following registers to enable this mode.
Address | Bit Values |
---|---|
0x137[7] | 1’b0 |
0x13C[7] | 1’b1 |
0x132[5:4] | 2’b01 |
0x142[4] | 1’b0 |
0x11D[0] | 1’b0 |
Disabling Reverse Serial Loopback Mode (Pre-CDR and Post-CDR)
To disable reverse-serial loopback mode, set the address bits to the following values, by performing read-modify-write.
Address | Bit Values |
---|---|
0x137[7] | 1’b0 |
0x13C[7] | 1’b0 |
0x132[5:4] | 2’b00 |
0x142[4] | 1’b0 |
0x11D[0] | 1’b0 |