Memory-mapped peripheral registers, remote protocol and memory maps

[Yao Qi]

On 11/29/2012 07:22 PM, Jon Beniston wrote:
> In some cases, there might be a large variety of inter-mixed
> 8/16/32-bit registers, which you might not have the space to cater
> for in a small stub. Can we be sure that GDB will only generate a 'm
> 0x0x00d000 4' packet? It would be tricky for a stub to deal with a

The following command 'p' will only generate 'm' packet with the right size.

(gdb) p *(unsigned int *) 0x8048608
Sending packet: $m8048608,4#3f...Packet received: 5589e583

(gdb) p *(char *) 0x8048608
Sending packet: $m8048608,1#3c...Packet received: 55

I admit they are tricky.

> packet of a larger size (say if the register area is opened in a
> memory viewer). Also, it would be nice to prevent reads from certain
> addresses, in case they have side effects (i.e FIFOs, etc).
>

Something similar was done in codesourcery (by other people) to handle 
memory-mapped register and side effect of reading registers (we call it 
read sensitiveness, IIRC).  The target description mechanism
(http://sourceware.org/gdb/current/onlinedocs/gdb/Target-Descriptions.html) 
was enhanced, in which the name, width, mapped address and read 
sensitiveness of each register is described.  With these knowledge, GDB 
can take care of memory-mapped register.  However, these patches didn't 
go to upstream.

-- 
Yao (齐尧)