I have a ARMv5-powered non-XScale device (the SHARP Brain™ electronic dictionary) with Windows Embedded CE 6.0 installed in NAND flash, and I use TCPMP to play my favorite AAC tunes and MPEG-4 movies.
But, when I start TCPMP, sometimes TCPMP freezes. So I looked into TCPMP and I managed to found that the freeze happens when this code is executed.
CheckARMXScale PROC
mov r0,#0x1000000
mov r1,#0x1000000
mar acc0,r0,r1 ; <--- here
mov r0,#32
mov r1,#32
mra r0,r1,acc0
cmp r0,#0x1000000
moveq r0,#1
movne r0,#0
cmp r1,#0x1000000 ;64bit or just 40bit?
moveq r0,#2
mov pc,lr
This code determines whether XScale is present by trying executing XScale instruction, and catching the exception if the "Undefined Instruction" exception was thrown.
The problem is that somehow the system fails to pass this exception to TCPMP properly, causing TCPMP to freeze. It seems to be not because of Windows CE, but rather because of buggy drivers in this device. Any driver updates are not expected since running TCPMP on this device is not officially supported.
I posted this issue to 2channel, and some people claimed that this way to determine if XScale is present is not good, but no one even tried to find a better way. So I googled and read through ARMv5 Architecture Reference Manual and so on, but I could find nothing. It appears that almost every program that utilizes XScale instruction set determines if XScale is present in the same way.
The question is that, is it possible to determine if XScale instruction set is present, without making use of any exception or any CPU mode except user mode?
(needs switching into kernel mode) read the CP15 register c0, Main ID register aka ID Code Register aka ARM CPUID. The top byte is the implementor which will be 0x69 ('i', Intel) for XScale.
Check also this thread.