ARM ARM1176JZF-S User Manual

The VFP Register File
ARM DDI 0301H Copyright © 2004-2009 ARM Limited. All rights reserved. 19-9
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19.6 Data transfer between memory and VFP11 registers
The B bit in the CP15 c1 Control Register, see Section B2 of the ARM Architecture Reference
Manual, determines whether access to stored memory is little-endian or big-endian. The
ARM11 processor supports both little-endian and big-endian access formats in memory.
The ARM11 processor stores 32-bit words in memory with the Least Significant Byte (LSB) in
the lowest byte of the memory address regardless of the endianness selected. For a store of a
single-precision floating-point value, the LSB is located at the target address with the lower two
bits of the address cleared. The Most Significant Byte (MSB) is at the target address with the
lower two bits set. For best performance, all single-precision data must be aligned in memory to
four-byte boundaries, and double-precision data must be aligned to eight-byte boundaries.
Table 19-5 lists how single-precision data is stored in memory and the address to access each
byte in both little-endian and big-endian formats. In this example, the target address is
0x40000000 .
For double-precision data, the location of the two words that comprise the data are stored in
different locations for little-endian and big-endian data access formats. Table 19-6 lists the data
storage in memory and the address to access each byte in little-endian and big-endian access
modes. In this example, the target address is
0x40000000 .
The memory image for the data is identical for both little-endian and big-endian within data
words. The ARM11 hardware performs the address transformations to provide both little-endian
and big-endian addressing to the programmer.
Table 19-5 Single-precision data memory images and byte addresses
Single-precision
data bytes
Memory address Little-endian byte address Big-endian byte address
MSB, bits [31:24]
0x40000003 0x40000003 0x40000000
Bits [23:16] 0x40000002 0x40000002 0x40000001
Bits [15:8] 0x40000001 0x40000001 0x40000002
LSB, bits [7:0] 0x40000000 0x40000000 0x40000003
Table 19-6 Double-precision data memory images and byte addresses
Double- precision
data bytes
Little-endian address
in memory
Little-endian
byte address
Big-endian address
in memory
Big-endian
byte address
MSB, bits [63:56]
0x40000007 0x40000007 0x40000003 0x40000000
Bits [55:48] 0x40000006 0x40000006 0x40000002 0x40000001
Bits [47:40] 0x40000005 0x40000005 0x40000001 0x40000002
Bits [39:32] 0x40000004 0x40000004 0x40000000 0x40000003
Bits [31:24] 0x40000003 0x40000003 0x40000007 0x40000004
Bits [23:16] 0x40000002 0x40000002 0x40000006 0x40000005
Bits [15:8] 0x40000001 0x40000001 0x40000005 0x40000006
LSB, bits [7:0] 0x40000000 0x40000000 0x40000004 0x40000007

ARM ARM1176JZF-S Specifications

General

Brand	ARM
Model	ARM1176JZF-S
Category	Computer Hardware
Language	English