Public bug reported:
The devmem2 utility allows the user to read/write physical memory space
in three widths: byte, halfword, and word. These casts are used to
handle the different widths:
switch(access_type) {
case 'b':
*((unsigned char *) virt_addr) = writeval;
read_result = *((unsigned char *) virt_addr);
break;
case 'h':
*((unsigned short *) virt_addr) = writeval;
read_result = *((unsigned short *) virt_addr);
break;
case 'w':
*((unsigned long *) virt_addr) = writeval;
read_result = *((unsigned long *) virt_addr);
break;
}
On a 64-bit system, unsigned long is 64 bits wide. In such a
configuration there is no way to read/write 32-bit values with devmem2;
the program jumps from halfword (16 bits) all the way to word (64 bits).
This can produce a surprising result when trying to poke 32-bit
registers on a PCI add-on card.
On embedded systems I normally use "busybox devmem" for this sort of
debugging, but the Ubuntu busybox packages do not have CONFIG_DEVMEM
enabled. I will file a separate change request on bugs.debian.org for
this.
More semi-related discussion about devmem2 vs. busybox here:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=595805
https://bugs.launchpad.net/ubuntu/+bug/607752
The problem was seen on devmem2 0.0-0ubuntu1 on Quantal.
** Affects: devmem2 (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1093748
Title:
32-bit accesses are missing on 64-bit systems
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