
Philips Semiconductors
PNX15xx Series
Volume 1 of 1
Chapter 15: Audio Output
PNX15XX_SER_3
Koninklijke Philips Electronics N.V. 2006. All rights reserved.
Product data sheet
Rev. 3 — 17 March 2006
15-4
Complex serial frames of up to 512 bits/frame
2.2 Memory Data Formats
The Audio Out unit autonomously obtains samples from memory in 16 or 32-bit per
sample memory formats, as shown in
Figure 2. Successive samples are always read
from increasing memory address locations.
The Audio Out implements a double buffering scheme in memory to ensure that there
are always samples available to transmit, even if the system controller is highly
loaded and slow to respond to interrupts. The software assigns two equal size buffers
in memory by writing 2 base addresses and a sample size to the corresponding
Prior to output transmission, if SIGN_CONVERT = 1, the MSB of the memory data is
inverted. This allows the use of external two’s complement 16-bit D/A converters to
generate audio from 16-bit unsigned samples. This MSB inversion also applies to the
‘0’ values transmitted to non-active output channels.
Note that the Audio Out hardware does not support A-law or m-law data formats. If
such formats are desired, the system DSP processor should be used to convert from
A-law or m-law data to 16-bit linear data.
2.2.1
Endian Control
Audio Out expects data to be supplied in little endian byte ordering mode. In little
endian byte ordering mode, the least signicant byte has the lowest memory address.
Figure 2:
Examples of Audio Out Memory DMA Formats
16 bit, stereo,
NR_CHAN=00
16 bit, stereo,
NR_CHAN=10
32 bit, stereo,
NR_CHAN=00
adr
SD[0].leftn
adr
SD[0].leftn
adr
SD[0].leftn
adr+2
SD[0].right n+1
adr+2
SD[0].right n
adr+4
SD[0].leftn+1
adr+4
SD[1].leftn
adr+4
SD[0].right n
adr+6
SD[0].right n+1
adr+6
SD[1].right n
adr+8
SD[0].leftn+2
adr+8
SD[2].leftn
adr+10
SD[0].right n+2
adr+10
SD[2].rightn
adr+8
SD[0].leftn+1
adr+12
adr+14
SD[0].leftn+3 SD[0].right n+3
adr+12
adr+14
SD[0].leftn+1 SD[0].right n+1
adr+12
SD[0].rightn+1
Table 2: Operating Modes and Memory Formats
NR_CHAN
MODE
Destination of Successive Samples
00
mono
SD[0].left
00
stereo
SD[0].left, SD[0].right
01
mono
SD[0].left, SD[1].left
01
stereo
SD[0].left, SD[0].right, SD[1].left, SD[1].right
10
mono
SD[0].left, SD[1].left, SD[2].left
10
stereo
SD[0].left, SD[0].right, SD[1].left, SD[1].right, SD[2].left, SD[2].right
11
mono
SD[0].left, SD[1].left, SD[2].left, SD[3].left
11
stereo
SD[0].left, SD[0].right, SD[1].left, SD[1].right, SD[2].left, SD[2].right, SD[3].left, SD[3].right.