BDM Linux driver modification.

Jacob W Janovetz janovetz at
Wed Oct 15 21:16:37 UTC 1997

Hello all,

   This is a note to people using the Linux BDM driver for 68k-based
designs of their own.

   I've recently diagnosed that my board doesn't work with the 
standard softwares available for BDM debugging because of a device
I designed in.  It's called a microprocessor voltage monitor.
Basically, it monitors the voltage and holds RESET low until
the voltage exceeds a threshold.  It also has a manual reset
input which it deglitches.  The result is that manual resets
are delayed a bit and the _minimum_ reset time is somewhere around
250 ms.  To some, this may seem like a superfluous device, but
it is definitely a nice thing to have in a system to avoid damage
to parts.

   In any case, the BDM driver allows BKPT to deassert only shortly
after RESET is deasserted.  If RESET is sent through the manual
reset input of the voltage monitor, that means the REAL RESET is
asserted much longer causing BKPT to beat RESET to the chip.  This
means that BDM mode is disabled.  (ahem!)

   I'm making some modifications to the BDM driver for Linux to
allow for this.  I don't expect it would be too useful to most 
people because I don't think many of the 68k circuits out there
use voltage monitors in this way.  However, I wanted to let 
people know that this is a a consideration they should make.


   janovetz at    | Once you have flown, you will walk the earth with
 University of Illinois | your eyes turned skyward, for there you have been,
                        | there you long to return.     -- da Vinci
        PP-ASEL         |

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