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From: jmonroy@netcom.com (Jesus Monroy Jr)
Subject: Test of the Intel 8254 shut-down/parity-check command
Message-ID: <jmonroyCDDv9y.Ew4@netcom.com>
Organization: NETCOM On-line Communication Services (408 241-9760 guest)
Date: Wed, 15 Sep 1993 06:56:21 GMT
Lines: 74
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========================================================================
Test of the Intel 8254 shut-down/parity-check command
-----------------------------------------------------
version: 1.0.0
date: 09-14-1993
author: jmonroy@netcom.com
Purpose: Test the for parity errors by shutting down
the RAM refresh timer.
While looking for the reason for DMA overruns
in the development of an FDC driver for
386bsd, suggestions were made that shutting
down the timer has no effect on the system;
reasons for this varied.
Compiling: I have made the code transportable.
It has been tested with:
MSDOS
-----
Zortech Personal C v. 1.07
Turbo C v. 2.01
Microsoft Quick C v. 2.50
386BSD
------
GNU C++ v. 1.39
How this works.
---------------
Simply the program issue a command to change
to mode 4 (described in the notes) with a "count-down"
value of 0x0a0a (2,570). This is done to timers 1 and 2,
the RAM refresh timer and the speaker timer, respectively.
Timer 0 is left running because most OSes cannot operate
without a timer for the "deadloop".
What should happen.
-------------------
On most 286 systems nothing will happen till a
interrupt is generated (I.E., keyboard pressed) or a RAM
chip finally loses it's charge. At this point, some system
will hang for a long while, some will immediately parity
error.
On 386bsd expect a "csh" coredump followed by a
system panic. The system will then reboot. On some systems
a parity error will never register.
What does this prove?
---------------------
Namely that the RAM refresh is controllable via
the i8254 timer on the IBM/ISA architecture.
___________________________________________________________________________
Jesus Monroy Jr jmonroy@netcom.com
Zebra Research
/386BSD/device-drivers /fd /qic /clock /documentation
___________________________________________________________________________