VSC7440 datasheet(257/444 Pages) MICROSEMI

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Functional Descriptions

VMDS-10492 VSC7440 Datasheet Revision 4.2

240

An entry in the TTI table is checked approximately every two clock cycles. If the TTI’s tick (configured

through TICK_IDX) has changed, then the TICK_CNT is decremented. If it becomes zero, the frame is

injected, and TICK_CNT is set to TIMER_LEN.

3.25.4.1 TTI Calendar

In default configuration, TTI table entries are serviced from 0-2047, then restarted again at entry 0.

When configuring the TTI table, the following must be considered:

•

It takes up to 4 clock cycles, worst-case, to service an entry in the TTI table.

•

A TTI must be serviced more frequently than the frequency of the TTI’s tick (see

TTI_TIMER.TICK_IDX).

This means that looping through the entire TTI table may take 2048 × 4 = 8192 clock cycles. With a clock

period of 4 ns, this corresponds to approximately 66 µs. In other words, no TTI must use a tick faster

than 66 us.

If TTIs faster than 66 µs are required, the TTI calendar can be used to have some entries in the TTI table

serviced more often than others, meaning the TTI table can be split into sections with TTIs using ticks of

different speeds.

The TTI calendar consists of four entries, as described in Table 6

The following illustration shows a configuration for the TTI calendar. In this case, only TTI entry 0-1023

are being used.

TTI_MISC_CFG

INJ_CNT_ENA

Enables counting of injected frames in

TTI_MISC:TTI_INJ_CNT.TTI_INJ_CNT.

Per TTI

Table 166 •

TTI Calendar Registers Overview

Field

Description

Replication

TTI_CAL_SLOT_PTRS SLOT_START_PTR

SLOT_END_PTR

Calendar slot’s frame table start and end pointer.

TTI_CAL_SLOT_CNT

SLOT_CNT

Number of TTIs to service in slot before moving to next

TTI calendar slot.

TTI_CTRL

TTI_CAL_LEN

Length of TTI calendar.

TTI_CTRL

TTI_INIT

When set, initializes calendar to start at calendar slot 0.

Cleared by AFI when done.

Table 165 •

TTI Parameters (2048 entries) (continued)

Field

Description

Replication

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