- Lock the RX PCS.
The RX PCS must be fully aligned before extracting VL Offset data. Wait for o_rx_pcs_fully_aligned to be asserted.
- Read the VL data for each of the Local Virtual Lanes (VL):
Perform the read operation from o_rx_pcs_status[mode] register via CSR interface. This returns VL data field data for all 20 virtual lanes.
- Set the Physical Lanes for each Remote Virtual Lane:Step through the data provided by each Local Virtual lane:
- Each lane provides a REMOTE_VL and a LOCAL_PL value.
For each of the 20 possible Remote virtual lanes, set PL[REMOTE_VL] = LOCAL_PL.
For example, if you read Local Virtual lane 12, and get back REMOTE_VL = 5, LOCAL_PL = 2, that means the data for Virtual lane 5 from the link partner is coming in on our Physical lane 2. You store that as PL[5] = 2.
- To calculate PTP timestamps, the MAC uses aligner information from the PCS to translate the timestamp of a random Serdes bit to that of an Alignment Marker bit. This difference is called the Virtual Lane Offset:For 100G/50G, the status registers in the register maps provide the Aligner information:
- ptp_vl_data_hi[19:0]
- ptp_vl_data_lo[19:0]
- ptp_lal[4:0] = This register indicates which local lane last received its alignment marker. This register is not used for VL OFFSET calculations
When a sync_pulse is received, the PCS snapshots its aligner states and stores them in ptp_vl_data_hi and ptp_vl_data_hi. The MAC reads this from CSRs and calculates the bits between bit 0 of the sync block and bit 0 of the last AM received (Virtual Lane Offset).
- Calculate the Virtual Lane Offsets for each of the Remote Virtual Lanes in bits:
For 100GE rate: Virtual Lane Offset = sync_pulse to last AM = gb_33_66_occupancy + gb_66_110_occupancy + blk_align_occupancy + am_detect_occupancy + am_count - local_lane_adjust- gb_33_66_occupency (in PL bits) = ptp_gb33_66_occupancy (from register map)
- gb_66_110_occupancy (in PL bits) = ptp_gb110_occupancy (from the register map)
- blk_align_occupancy (in VL bits) = ptp_blk_align_occupancy (from register map) x 5 to convert to PL bits.
- am_count (in VL blocks) = ptp_am_count (from the register map) x 66b/block x 5 to convert to PL bits
- local_lane_adjust (in PL bits) = local_vl %5 (This is the bit offset of the local lane’s bit 0 from bit 0 of the interleaved sync block from PHY)
For 50GE rate: Virtual Lane Offset = sync_pulse to last AM = gb_33_66_occupancy + sep50_occupancy + blk_align_occupancy + am_detect_occupancy + am_count - local_lane_adjust
- gb_33_66_occupancy (in PL bits) = ptp_gb_33_66_occupancy from the register map
- sep50_occupancy (in PL bits) = ptp_gb110_occupancy from the register map
- blk_align_occupancy (in VL bits) = ptp_blk_align_occupancy from the register map, x 2 to covert to PL bits
- am_detect_occupancy (in VL bits) = ptp_am_detect_occupancy from the register map, x2 to convert to PL bits
- am_count (in VL blocks) = ptp_am_count from the register map, x66b/block x 2 to convert to PL bits
- local_lane_adjust (in PL bits) = local_vl %2 (This is the bit offset of the local lane’s bit 0 from bit 0 of the interleaved sync block from PHY)
- Apply shifts to the offsets for REMOTE_VLs {18..19} to account for the mii_am/mii_data reordering that happens in the PCS MII Decoder. This step is applicable for 50GE-2 and 100GE rates only.
- Generate vl_offset_bits shifted for each of the REMOTE_VLs.
- When using RX PTP on data from the RX PCS, shift the times for REMOTE_VLs 18 to 19 by -330 bits:
vl_offset_bits_shifted[REMOTE_VL] = vl_offset_bits[REMOTE_VL] -330 for REMOTE_VL == {18..19} vl_offset_bits_shifted[REMOTE_VL] = vl_offset_bits[REMOTE_VL] for REMOTE_VL == {0..17}This shift accounts for a shift that is applied by the RX PCS to incoming data.
For example, if vl_offset_bits[18] == 887, set vl_offset_bits_shifted[18] to 557. If vl_offset_bits[17] == 887, set vl_offset_bits_shifted[17] to 887.
Note: For 50GE-2 rates, follow same instructions except only apply the shifting to VL3. - Convert the vl_offset_bits to VL_OFFSET (in ns):
For each REMOTE_VL, VL_OFFSET[REMOTE_VL] = vl_offset_bits_shifted[REMOTE_VL] * RX_UI