VP2612CGGPFR 데이터 시트보기 (PDF) - Mitel Networks

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VP2612CGGPFR

Video Multiplexer

Mitel Networks 

VP2612

monitoring is, however, done by the FEC block as described

later.

The two address pointers can be read by the system

processor, thus allowing the level of the buffer to be monitored.

These are provided as 16 bit words with no truncation, and thus

require two bytes. The 16 bit value is internally frozen when the

most significant byte is requested by the system processor, and

for accuracy the write pointer should be read first. There is also

a control register bit which selects a buffer size of either 256kbits

or 512kbits.

FEC Block

The FEC section performs the framing, and adds the error

correction parity bits. If sufficient data for a frame is not available

in the transmission buffer, then the frame will be stuffed

automatically. There is no absolute threshold at which the FEC

will start to stuff, as the buffer level monitor in the FEC only works

to a resolution of ±128bits. FEC stuffing can also be forced by

setting the "Force FEC stuffing" bit in the VMUX/FEC control

register.

If the buffer level reaches a threshold, internally set to 512

short of the buffer being full, the OVERFLOW output is asserted.

DMODE3:0

FUNCTION

0000

0001

0010

0011

0100

0101

0110

0111

1000

1001

1010

1011

1100

1101

1110

1111

GOB Number

MB Number

Control Decisions

Quant Value

Horizontal MV

Vertical MV

Coded Blk Pattern

Sub-Block No.

Zero Run Count

RLC Coefficient

Not Used

Not Used

Not Used

Not Used

Not Used

Wait State

Table 1

This is to warn the system processor that drastic action is

needed to avert a buffer overflow, which will result in corruption

and loss of data. Since the buffer level monitor only works to

resolution of ±128bits, then the overflow detection can only be

accurate to ±128bits.

VP2611 Interface

The VMUX has been designed to interface directly to

the VP2611 encoder, with no buffering. The interface consists

of two buses DBUS7:0 and DMODE3:0, and a strobe signal

DCLK. The value on DMODE3:0 identifies the data type on

DBUS7:0 during the same period (see Table 1).

The output of the VP2611 is structured such that the

data on DBUS7:0 and DMODE3:0 is always valid for at

SCLK

DCLK

25ns max

25ns max

DATA FROM

VP2611

20ns max

DATA VALID

DMODE

3:0

DATA VALID

Figure 2. DBUS Timing

least two cycles, and DCLK is high for minimum of one

cycle. The rising DCLK edge occurs one cycle after

DBUS7:0 and DMODE3:0 are valid, as shown in Figure 2.

The sequence of events, and the duration of each

event, is shown in Figure 3. These duration times have

been chosen to satisfy the internal requirements of the

VP2612, and Wait States are inserted such that the time

to transfer a macroblock is always 2064 SCLK periods.

The parameters used by the VP2612 are described

in more detail below;

GOB Number : The current GOB Number is provided on

DBUS3:0 after the Control Decisions byte. (DBUS3 is

MSB).

MB Number : After the GOB Number, the macroblock

Number is provided on DBUS5:0 (DBUS5 is MSB).

Control Decisions : This byte shows which control decisions

have been taken for the forthcoming macroblock, and is

the first in the sequence. DBUS0 will be high if a Fixed

Macroblock (FIX MB) was enforced i.e. no new data will

be transmitted this macroblock. DBUS1 indicates

whether Inter (high) or Intra (low) coding was used for the

macroblock. DBUS2 will be high if the macroblock was

filtered, and DBUS3 will be high if motion compensation

was used. DBUS5 will be high if the current frame is being

coded in FAST UPDATE mode. In this mode the com-

plete frame will be intra coded. DBUS6 will be high if the

current frame is a SKIP FRAME i.e. not being coded - so

no coefficients will be transmitted. DBUS4 and DBUS7

are not used.

Quant Value :The quantisation value used in processing the

current macroblock is provided on DBUS4:0 (DBUS4 is

MSB). This represents an actual quantisation level be-

tween 2 and 62, in steps of 2 and as defined in H.261.

Horizontal MV : If motion compensation was used the hori-

zontal component of the motion vector will be provided on

DBUS4:0 (DBUS4 is MSB). (This 5 bit value represents

a two's complement number in the range (-15 to +15)

(although only vectors in the range +7/-8 are currently

possible with the VP2611). If motion compensation was

not used this is a don't care value.

3

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