MFC2000 datasheet(267/426 Pages) ETC

267 / 426 page

Multifunctional Peripheral Controller 2000

MFC2000

100723A

Conexant

14-1

14. Compressor and Decompressor

14.1 Functional Description

The T.4 data compression/decompression process is primarily implemented in hardware within the MFC2000

(see Figure 14-2). Hardware provides compression and decompression of data within a line, and adds fill bits at

the end of a line to cause the number of bits (coded plus fill) to be a multiple of 16 (halfword justified) for T.4 MH

and MR. For coding (compression), firmware (T.4 subsystem task) appends end-of-line characters and, if

required, fill bits to support the minimum line times of CCITT T.4. On the receive side, firmware passes the coded

line to the T.4 hardware. Data flow control, to prevent buffer overflow/underflow, is also the responsibility of the

firmware.

Line times less than 5 msec per line are supported by the MFC2000s' T.4 hardware; the line time supported by

the overall system depends on other system factors (e.g. resolution, concurrency, etc). T4 line lengths up to 2046

bytes are supported.

There are three FIFOs contained in the compressor/decompressor block. All FIFOs operate identically from both

a hardware and firmware standpoint. The FIFO structure is illustrated in Figure 14-2. The FIFOs consist of a quad

halfword FIFO structure and a single halfword holding register. The quad FIFO structure is emptied and filled by

either DMA or CPU operations. The holding register is emptied and filled by the compressor/decompressor logic.

All locations within the FIFO can also be arbitrarily read and written by firmware. This allows firmware to save the

entire FIFO state and restore it at a later point in time, thereby permitting an unlimited number of data streams to

be concurrently processed.

Mux

T4 (MH, MR),

T6(MMR)

Code or

Decode

Line

CPU Data

DMA Ch 10

Data

DMA Ch 7

DMA Ch 6

T4 Bi-Level

Resolution

Conversion

DMA Ch 8

T4/T6 Compression/Decompression

T4Data

FIFO3

Current Line

Buffer Data

(Uncoded Data)

Reference Line

Buffer Data

(Uncoded Data)

Figure 14-1. Data Flow for Compression/Decompression

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