Sabre32 Reference Datasheet

February 11, 2010

CONFIDENTIAL ADVANCE

INFORMATION Rev. 1.2

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23

Vista™

High Definition

Vista™

High Definition

FIR PROGRAMMABLE FILTERS

The SABRE

32 Reference has a two stage interpolating filter with both built-in and programmable

coefficients. Each stage can be programmed and enabled independently. Each channel can also have a

different filter per stage.

Each stage of the FIR filter either uses the built-in coefficients, or the programmable coefficients.

Register 37 bits 5 and 1 are used for setting the filter coefficient sources.

Programming the filter requires passing every coefficient for all 8 channels to the SABRE

32 Reference via

I2C. Stage 1 and Stage 2 must be programmed independently. Programming starts by enabling the

appropriate enable_programming bit in register 37.

To program stage 1, bit 4 of register 37 must be set high. Then the 32bit coefficients are written to

registers 41 (Bits [31:24]), 40 (Bits[23:16]), 39 (Bits[15:8]), 38 (Bits[7:0]) in that order. The first write to

these 4 consecutive register is the 32-bit value for Channel1, coefficient1. The next write to these 4

consecutive registers is the 32-bit value for Channel2, coefficient1. After 8 writes to these 4 consecutive

registers, coefficient 2 for all 8 filters is ready to be input.

There are 64 coefficients to write for Stage 1.

So that is 4 bytes per coefficient, 8 channels and 64 coefficients for a total of 2048 bytes to program the

stage 1.

Once complete, zero must be written to register 38. Bit 4 of register 37 must then be set low to

finalize the programming.

To program stage 2, bit 0 of register 37 must be set high. Then the 32bit coefficients are written to

registers 45 (Bits [31:24]), 44 (Bits [23:16]), 43 (Bits [15:8]), 42 (Bits [7:0]), in that order. The first write to

these 4 consecutive register is the 32-bit value for Channel1, coefficient1. The next write to these 4

consecutive registers is the 32-bit value for Channel2, coefficient1. After 8 writes to these 4 consecutive

registers, coefficient 2 for all 8 filters is ready to be input.

There are 16 coefficients to write for Stage 2.

So that is 4 bytes per coefficient, 8 channels and 16 coefficients for a total of 512 bytes to program the

stage 1.

Once complete, zero must be written to register 42. Bit 0 of register 37 must then be set low

to finalize the programming.

C++ Sample Code for writing custom coefficients to either stage.

void CLoadCoeffDlg::ProgramStage(int nStage)

{

BYTE WE;

BYTE WritePort[4];

BYTE WriteData[4];

int nTotal;

if(nStage==0){

//programming stage 1

WE=0x10;

WritePort[0]=41;

WritePort[1]=40;

WritePort[2]=39;

WritePort[3]=38;

nTotal=64;

}

else{

//programming stage 2

WE=0x01;

WritePort[0]=45;

WritePort[1]=44;

WritePort[2]=43;

WritePort[3]=42;

nTotal=16;