The end to end latency is always fixed and made up of one LEMC period plus the fixed TX and RX delays. To calculate the end to end latency, use the following steps, referring to the following figure.
The delay between LEMC at TX and LEMC at RX (T) is the LEMC period adjusted by the internal delays from SYSREF to LEMC of TX and RX:
T = LEMC - TTXLEMC + TRXLEMC
To ensure the overall propagation delay is constant between system restarts, the maximum propagation delay must be less than T:
TTXOUT(max) + TWIRE(max) + TRXIN(max) < T
Substituting LEMC - TTXLEMC + TRXLEMC for T gives:
TTXOUT(max) + TWIRE(max) + TRXIN(max) < LEMC - TTXLEMC + TRXLEMC
Additional delay can be added to the SYSREF processing in the JESD204C core (see Table 15). For each cycle of delay added to TX SYSREF, add 1 to TTXLEMC.
The data is received after the fixed delays of TX and RX adjusted by the internal delays from SYSREF to LEMC of TX and RX. This value is also the minimum value for deterministic latency.
TLAT = TTXOUT(max) + TWIRE(max) + TRXIN(max) - TTXLEMC + TRXLEMC
| JESD204C + GT Latency | Assume a DAC with Parameters | Assume |
|---|---|---|
| TTXLEMC = 6 words | TRXIN = 12±1 words | TWIRE = 0 |
| TTXOUT = 14±1 words | TRXLEMC = 1 word | LEMC = 64 words |
| TTXIN = 0 | TRXOUT = 5 words |
TTXOUT(max) + TWIRE(max) + TRXIN(max) < LEMC - TTXLEMC + TRXLEMC
15 + 0 + 13 < 64 - 6 + 1
28 < 59
The data is received after the fixed delays of TX and RX adjusted by the internal delays from SYSREF to LEMC of TX and RX.
TLAT = TTXOUT(max) + TWIRE(max) + TRXIN(max) - TTXLEMC + TRXLEMC
TLAT = 15 + 0 + 13 - 6 + 1
TLAT = 23 clock cycles