14-6
Intel® PXA255 Processor
Developer’s Manual
Inter-Integrated-Circuit Sound (I2S) Controller
The BITCLK, as shown in
Table 14-2
, is different for different sampling frequencies. If the
BITCLK is chosen as an output, the Audio Clock Divider Register divides the 147.46MHz PLL
clock to generate the SYSCLK. The SYSCLK is further divided by four to generate the BITCLK.
The sampling frequency is the frequency of the SYNC signal, which is generated by dividing the
BITCLK by 64. See
Section 14.6.4
, for further details about the register.
A sampling rate of 48kHz supports MPEG2 and MPEG4. A rate of 44.1kHz supports MP3.
14.5
Data Formats
14.5.1
FIFO and Memory Format
FIFO buffers are 16 levels deep and 32 bits wide. This stores 32 samples per channel in each
direction.
Audio data is stored with two samples (Left + Right) per 32-bit word, even if samples are smaller
than 16 bits. The Left channel data occupies bits [15:0], while the Right channel data uses bits
[31:16] of the 32-bit word. Within each 16-bit field, the audio sample is left-justified, with unused
bits packed as zeroes on the right-hand (LSB) side.
In memory, the mapping of stereo samples is the same as in the FIFO buffers. However, single-
channel audio occupies a full 32-bit word per sample, using either the upper or lower half of the
word, depending on whether it’s considered a Left or Right sample.
14.5.2
I
2
S and MSB-Justified Serial Audio Formats
I
2
S and MSB-Justified are similar protocols for digitized stereo audio transmitted over a serial
path.
The BITCLK supplies the serial audio bit rate, the basis for the external CODEC bit-sampling
logic. Its frequency is 64 times the audio sampling frequency. Divided by 64, the resulting 8 kHz to
48 kHz signal signifies timing for Left and Right serial data samples passing on the serial data
paths. This Left/Right signal is sent to the CODEC on the SYNC pin. Each phase of the Left/Right
signal is accompanied by one serial audio data sample on the data pins SDATA_IN and
SDATA_OUT.
Table 14-2.
Supported Sampling Frequencies
Audio Clock
Divider
Register
(31:0)
SYSCLK =
147.6 MHz / (SADIV)
BITCLK =
SYSCLK / 4
SYNC or Sampling frequency =
BITCLK / 64
0x0000_000C
12.288 MHz
3.072 MHz
48.000 kHz (closest std = 48 kHz)
0x0000_000D
11.343 MHz
2.836 MHz
44.308 kHz (closest std = 44.1 kHz)
0x0000_001A
5.671 MHz
1.418 MHz
22.154 kHz (closest std = 22.05 kHz)
0x0000_0024
4.096 MHz
1.024 MHz
16.000 kHz (closest std = 16.00 kHz)
0x0000_0034
2.836 MHz
708.92 kHz
11.077 kHz (closest std = 11.025 kHz)
0x0000_0048
2.048 MHz
512.00 kHz
8.000 kHz (closest std = 8.00 kHz)
Summary of Contents for PXA255
Page 1: ...Intel PXA255 Processor Developer s Manual January 2004 Order Number 278693 002 ...
Page 24: ...xxiv Intel PXA255 Processor Developer s Manual Contents ...
Page 30: ...1 6 Intel PXA255 Processor Developer s Manual Introduction ...
Page 310: ...7 46 Intel PXA255 Processor Developer s Manual LCD Controller ...
Page 330: ...8 20 Intel PXA255 Processor Developer s Manual Synchronous Serial Port Controller ...
Page 358: ...9 28 Intel PXA255 Processor Developer s Manual I2 C Bus Interface Unit ...
Page 488: ...13 36 Intel PXA255 Processor Developer s Manual AC 97 Controller Unit ...
Page 572: ...16 30 Intel PXA255 Processor Developer s Manual Network SSP Serial Port ...
Page 599: ...Intel PXA255 Processor Developer s Manual 17 27 Hardware UART ...
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