pnx1700 NXP Semiconductors, pnx1700 Datasheet - Page 812

• Manufacturer Part Number: pnx1700
• Description: Connected Media Processor
• Manufacturer: NXP Semiconductors

Philips Semiconductors
Volume 1 of 1
PNX17XX_SER_1
Preliminary data sheet
4.3 Module DMA
4.4 SIMD Programming Issues
4.5 Optional Endian Mode Override
Every DMA capable module in PNX17xx Series observes the system big-endian
signal, and therefore the global SYS_ENDIANMODE.BIG_ENDIAN value, to
determine how to write each data item or unit to memory.
An example of a unit would be:
The module performs byte swapping within units as needed, and packs units as
needed for transmission across on-chip buses. Byte swapping is done in such a
fashion that 8, 16 and 32-bit units always end up in memory bytes in the form
prescribed by the CPU rule. Successive item packing are placed in incrementing
addresses, as designated by the DMA rule.
The module DMA hardware architecture ensures that software dealing with loads and
stores of unit size data can be written in a way that is oblivious to the endian mode.
With the current TM32 CPU core, this is not possible for software that performs Single
Instruction Multiple Data (SIMD) style programming using multimedia operations.
Consider the case of a FIR filter, operating on 16-bit sample units, but using
2-at-a-time load/store/multiply operations. Which of the two 16-bit halfwords is the
earlier sample?
The current TM32 CPU core on PNX17xx Series requires that SIMD software be
written aware of endian mode.
Some PNX17xx Series DMA modules have bits in a control register that allow
override of the global endian mode. Refer to each module for details. This method is
used only in modules that deal with DMA of data of a single, fixed size (in a given
mode). Such modules implement a field that allows selection of the following modes:
•
•
•
•
•
•
•
•
•
16-bit audio sample
32-bit audio sample
32-bit unit containing a RGBa 8888 true color pixel with alpha value.
For big-endian mode, the msb halfword contains the earlier sample.
For little-endian mode, the lsb halfword contains the earlier sample.
Normal mode (reset default), obey global PNX17xx Series endian mode
Explicit little-endian, unswapped
Swap over 16 bits
Swap over 32 bits
Rev. 1 — 17 March 2006
© Koninklijke Philips Electronics N.V. 2006. All rights reserved.
PNX17xx Series
Chapter 29: Endian Mode
29-8