Visible to Intel only — GUID: iqb1661431625132
Ixiasoft
Visible to Intel only — GUID: iqb1661431625132
Ixiasoft
30.3.1. Switch IP Latency
The minimum switching latency (Lswitch) is the number of clock cycles from the submitting of a new switch configuration via a write to the COMMIT register, to the start of the first image information packet (full variants) or first line (lite variants) produced at the configured outputs.
Lswitch = Tremaining + 8 + (C ? 6 : 3)*I + 8*O
where
- Tremaining = the number of cycles from the write to COMMIT to the end-of-field packet of the current input field (for full variants) or to the TLAST of the current line (lite variants) or to the next TUSER[0] (lite variants with All inputs are uninterrupted on).
- I = The number of inputs whose state is changing (either consume, enable, disable or destination)
- O = The number of outputs whose state is changing (either enable, disable, or source)
- C is 1 with Autoconsume inputs on.
This equation holds in the absence of backpressure and in a fully synchronized system with all switch inputs receiving fields of the same size at the same time, and common host and main clocks.
Latency in a real system is dominated by the timing of the input fields and Lswitch usually only represents a very small percentage of overall switching time.
The fastest switching configurations are lite variants with All inputs are uninterrupted off, as changes occur at line endings, not field endings.