pnx1700 NXP Semiconductors, pnx1700 Datasheet - Page 811

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

Philips Semiconductors
Volume 1 of 1
4. PNX17xx Series Endian Mode Architecture Details
PNX17XX_SER_1
Preliminary data sheet
4.1 Global Endian Mode
4.2 Module Control
The programmer’s view of the PNX17xx Series endian architecture is as follows:
The CPU and all the modules always operate in a single endian mode. This endian
mode is determined by the BIG_ENDIAN bit in the SYS_ENDIANMODE register of
the PNX17xx Series Global register module. The value of this bit is set during system
boot and normally not changed afterward.
Remark: The TM32 CPU core endian mode is determined by a bit in its PCSW. This
is historically set by the “crt0.s” software module on the TM32 CPU core, which
initializes the PCSW. The PNX17xx Series version of this software module is
responsible for reading the SYS_ENDIANMODE.BIG_ENDIAN bit value and
establishing the same TM32 CPU core endian mode as the rest of the system.
All the modules have Control and Status registers, accessed by CPU Programmed I/
O. In the PNX17xx Series, all programmed I/O happens through Memory Mapped I/O
registers. A separate Device Control and Status Bus (DCS Bus) is used for all MMIO
programming. A CPU can access Device Control and Status registers by using the
correct MMIO address for a module register. In the PNX17xx Series, all module
registers are 32 bits wide and may only be accessed through 32-bit load/store
operations.
A control/status register load/store always copies the 32 bits verbatim between a
CPU register and the module register. The module’s left-most msb (bit 31) ends up in
the CPU’s left-most msb (bit 31), and the module’s right-most lsb (bit 0) ends up in the
right-most CPU register bit. This happens regardless of system endian mode
settings.
MMIO load and store instructions always see the same bit layout of module MMIO
registers, regardless of endian mode. The field and bit layout is precisely as specified
in the module register table with bit 31 designating the msb and bit 0 the lsb.
Remark: The packing and ordering of packed bit structure fields in C compilers are
not precisely defined. Typically, big-endian C compilers pack fields from left (msb) to
right (lsb). Little-endian C compilers pack from right to left. Because of this and also
because of inherent inefficient code when accessing structure fields, it is not
recommended to use C structure declarations to access MMIO register fields.
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The CPU and the modules on the PNX17xx Series store and retrieve audio
samples, image pixels and data observing both the CPU rule and DMA rule.
The system as a whole runs in either little-endian or big-endian mode.
The mode is determined by the “BIG_ENDIAN” bit in the SYS_ENDIANMODE
register, see
which is “exported” to other modules.
The value of this bit is set during system initialization.
Chapter 3 System On Chip Resources Section 3.3 on page
Rev. 1 — 17 March 2006
© Koninklijke Philips Electronics N.V. 2006. All rights reserved.
PNX17xx Series
Chapter 29: Endian Mode
3-8,
29-7