For example:
01.1111111111
01.0000000000
00.0000000000
11.0000000000
10.0000000000
=
=
=
=
=
most positive number, close to
2
1
0
-1
-2
, most negative number
Equation 9.1 shows the equation for the IIR filter. Equation 9.2 shows the equation for when the DC blocking is
enabled.
The filter is configured, enabled and disabled from the VM via the
CodecSetIIRFilterA
and
CodecSetIIRFilterB
traps. This requires firmware support. The configuration function takes 10 variables in the
following order:
0
1
2
3
4
5
6
7
8
9
:
:
:
:
:
:
:
:
:
:
Gain
b
01
b
02
a
01
a
02
b
11
b
12
a
11
a
12
DC Block (1 = enable, 0 = disable)
Filter, H(z) = Gain ×
( 1 + b01 z
−1 + b
02 z
−2 )
( 1 + a01 z
−1 + a
02 z
−2 )
×
( 1 + b11 z
−1 + b
12 z
−2 )
( 1 + a11 z
−1 + a
12 z
−2 )
Equation 9.1: IIR Filter Transfer Function, H(z)
Filter with DC Blocking, H
DC
(z) = H(z) × ( 1 − z
−1
)
Equation 9.2: IIR Filter Plus DC Blocking Transfer Function, H
DC
(z)
9.3
PCM1 Interface
There are 2 digital audio interfaces. Each is independently configurable as an I²S, PCM or SPDIF port. The PCM1
interface also shares the same physical set of pins with the SPI interface, see Section 7.3 and Section 8.1. Either
interface is selected using SPI_PCM#:
■
SPI_PCM# = 1 selects SPI
■
SPI_PCM# = 0 selects PCM
Important Note:
The term
PCM
refers to PCM1.
Advance Information
This material is subject to CSR's non-disclosure agreement
© Cambridge Silicon Radio Limited 2011
Page 47 of 110
CS-209182-DSP1
CSR8640 BGA
Data Sheet
