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Re: [avr-gcc-list] port access with avr-gdb
From: |
Theodore A. Roth |
Subject: |
Re: [avr-gcc-list] port access with avr-gdb |
Date: |
Thu, 17 Jun 2004 10:25:02 -0700 (PDT) |
On Thu, 17 Jun 2004, David Willmore wrote:
> > - If you were to use this structure to print out the values of all the
> > io registers using a gdb command like this:
> >
> > (gdb) print *((struct _avr_regio *)0)
> >
> > you could get some nasty side effects. Reading some registers changes
> > the state of the MCU (e.g. reading UDR). There's also no guarantee
> > about what happens when you read/write a reserved register. (I vaguely
> > remember hearing that some reserved registers have secret functionality
> > used by Atmel during testing - I could be quite wrong about this
> > though).
>
> Even if you read the register with JTAG? I guess if the JTAG method of
> reading is like the PIC debug method where you clock an instruction into
> the core to fetch a register and then watch to see the data that comes
> onto the bus, then, to the chip, it can't really tell the difference.
> Rats.
OK, the side effects might be under control by the config array that
avarice sends down to the jtagice box at init time. Have a look the
jtag_device_desc_type structure here:
http://cvs.sourceforge.net/viewcvs.py/avarice/avarice/src/jtag.h?rev=1.15&view=auto
It looks like the structure explicitly tells the jtagice box which io
address in io reg space are readable and writeable.
Although, I had a discussion a while back with David Gay about him
seeing strange behaviour when reading reserved registers. I think he
said that he was reading non-zero values from reserved registers...
>
> I sure wish people would quit designing 'clever' hardware like that. What's
> wrong with just setting a flag bit to say you read it? *sigh* People try
> to be too clever.
Loks like the jtagice developers were clever with the config array, but
since we can't examine the firmware, we don't know if their
implementation does the right thing. I hope that the firmware will
intercept reads/writes to addresses that it's not supposed to pass on to
the jtag tap controller...
---
Ted Roth
PGP Key ID: 0x18F846E9
Jabber ID: address@hidden
- RE: [avr-gcc-list] port access with avr-gdb, (continued)
- RE: [avr-gcc-list] port access with avr-gdb, Dave Hylands, 2004/06/13
- RE: [avr-gcc-list] port access with avr-gdb, Larry Barello, 2004/06/16
- RE: [avr-gcc-list] port access with avr-gdb, Theodore A. Roth, 2004/06/17
- RE: [avr-gcc-list] port access with avr-gdb, Theodore A. Roth, 2004/06/17
- Re: [avr-gcc-list] port access with avr-gdb, David Brown, 2004/06/17
- RE: [avr-gcc-list] port access with avr-gdb, Larry Barello, 2004/06/17
- RE: [avr-gcc-list] port access with avr-gdb, Theodore A. Roth, 2004/06/17
- Message not available
- RE: [avr-gcc-list] port access with avr-gdb, Theodore A. Roth, 2004/06/17
Re: [avr-gcc-list] port access with avr-gdb, Ned Konz, 2004/06/18
Re: [avr-gcc-list] port access with avr-gdb,
Theodore A. Roth <=
Re: [avr-gcc-list] port access with avr-gdb, David Brown, 2004/06/18
RE: [avr-gcc-list] port access with avr-gdb, Dave Hylands, 2004/06/18
RE: [avr-gcc-list] port access with avr-gdb, Dave Hylands, 2004/06/18
RE: [avr-gcc-list] port access with avr-gdb, Dave Hylands, 2004/06/21