Shareware Grab Bag/Shareware Grab Bag.iso/090/cscv.arc/CSVS.DOC

Text File | 1987-04-20 | 29KB | 521 lines

                The Computer Shopper PC Clone Validation Test
                    By Andrew M. Fried & Kenneth McMillen

Introduction
------------
There has never been a better time to purchase an IBM clone microcomputer than
today.   Overseas  production and fierce competition have  made  the  computer
consumer master of the industry.

There  is  generally  one question facing most  prospective  buyers  of  clone
computers,  and  that  is  whether  or not the system  is,  in  fact,  a  true
compatible.

Beginning next month, Comupter Shopper will add another program to its list of
programs  used  to  test a systems compatibility with that of  the  PC.   This
program, called BIOSTEST, invokes almost all of the ROM BIOS calls and  checks
them for proper operation.

The purpose of this article is to discuss the various interrupts available  in
ROM BIOS and how they can be checked for compatiblity.


Interrupt 5 - Print Screen
--------------------------
When  the combination of the Shift-PrtScr keys are  simultaneously  depressed,
the  ROM  BIOS  generates  an interrupt type 5.   This  interrupt  causes  the
contents of the screen to be sent to LPT1:.

Our  test of this interrupt is simple and straightforward.  To begin  with,  a
ROM  BIOS  call is made to determine the current video mode.  Once  the  video
mode is known, the active screen memory is known.

The contents of the current screen are saved into a buffer so that they may be
restored  upon completion of the test.  In order to insure that there  is,  in
fact, something on the screen to print, a series of printable ASCII characters
are  generated  and displayed onto the active screen.   These  characters  are
printed sequentially from chr(32) up to chr(127).

BIOSTEST then generates an Interrupt 5.  It becomes the responsibility of  ROM
BIOS to transfer everything on the screen onto the printer.

Once the interrupt has finished, BIOSTEST restores the screen to its  original
condition and waits for you to press a key to continue.  In order to determine
whether or not the interrupt functioned properly, you must examine the printer
output to see if the pattern appears correct.


Interrupt 10 - Video I/O
------------------------
ROM-BIOS  has a set of routines which handle various video   functions.  These
routines set screen modes, move and find the  cursor's position, select active
graphic  pages,  up/down  scrolling, read/write  characters  with  attributes,
read/write  dots, and color selections. Some of them are practical if  program
speed  is not a problem. However if you wish to do some  fancy  graphics  that
are  quick  then using these routines are not  for you. Their  performance  is
slow as you will see with the dot  testing. The nicer functions are the screen
scrolling  and active  page selection. To take advantage of the  graphics  you
will need  a color monitor.

Before  the test begins it checks to see what type of monitor  you are  using.
If  you  are using a monochrome monitor the program  will only  do  the  tests
which  apply to a monochrome display.  There are sixteen functions  with  this
interrupt.  The test will  step through each one and ask you to press any  key
at  the  end of  each test to continue on to the next one. Some of  the  tests
will   display a pass or fail message while the rest of them require  you   to
look at the screen to verify certain conditions. Each of the  tests will  have
a header at the top of the screen to let you know  what is being tested.

The first test that is tried is the verification of a table  in ROM-BIOS  that
contains video initialization parameters. When  you boot your system or  power
it  on the built in diagnostics look  at the switch settings for  the  monitor
type  and set up the video  card with the correct parameters from this  table.
If  one of the  parameters do not match then the test fails. This table  needs
to  match 100% if you system is to be compatible.

The next test deals with setting screen modes. If you are  using a  monochrome
display  then there is only one mode. For the  color display there  are  seven
different modes. You should see  each of the seven modes set (40x25 BW,  40x25
color, 80x25 BW,  80x25 color, 320x200 color, 320x200 BW, and 640x200 BW).

Using  this next function you can set up your cursor type.  In the  monochrome
mode  your cursor is made up of thirteen lines  whereas in the color mode  you
have  just seven. If you use this  function it needs the starting  and  ending
line.  This test should  display a solid cursor, starting at cursor line  zero
and ending  at seven or thirteen.

The  next two tests position and read the cursor's location.  The  first  test
positions  the cursor at row four, column twelve  and prints the  letter  'X'.
You  need  to verify this by looking at  the screen. The other test  does  the
same  thing and then reads  the location of the cursor which should be at  row
four,  column  thirteen. On the screen you should see the blinking  cursor  at
this position. Press any key when you have finished with each  test.

Function  number  four of this interrupt reads the position of  a  light  pen.
This test was not included since most everyone does  not have a light pen.

Function number five selects the active page to display. To  fully utilize all
of  the memory on the video card IBM included  this function which  gives  you
multiple  pages  of text. In a 40x25  screen mode you have a  total  of  eight
pages of text that you  could flip through if your application takes advantage
of  this.   In an 80x25 mode you get just four since you are  using  twice  as
much  video  memory. This function works only with color displays.   The  test
will  first  use  the 80x25 mode and fill up all four  pages   with  the  page
number. Then the test will ask you to press any  key to flip through the  four
pages verifying that each screen  page is filled with the proper page  number.
If so then this test  passes.

The  next  two tests test the scrolling functions. The first   one  fills  the
screen with text and scrolls up a window of text.  The second on does the same
except it scrolls down a window of  text. If you see this happen then both  of
these tests pass. You  can also see what the character set will look like.

The  next  three tests deal with the character handling  routines.  The  first
will  display  a  test  pattern made up  of  all   the  attribute  capabilites
(underline,  color,  blinking...). The  test will read the  pattern  from  the
screen  and  if  it matches the  test passes. The next test  writes  the  test
pattern  on  the screen  and then it is read back to verify that  the  pattern
matches.  If   so then this test passes. The third test also writes  the  test
pattern  to the screen but without any of the attributes so what   you  should
see  is text displayed normally. A trade off with the  attributes is that  you
have  the underline capability only with  the monochrome and color  only  with
the color display.

Functions eleven, twelve, and thirteen are used for  graphics. Function eleven
sets  the  color palette. The test  should cycle through sixteen  colors.  You
will  need to verify  this. Function twelve handles writing dots or pixels  to
the  screen at a particular row and column. The test should draw a  box on the
screen. To verify that the test did this it will read  back all the dots which
make up the box, please be patient while  the test does this. If they are  all
read  back  successfully  then  the test  passes.  Function  thirteen  handles
reading  the  color  of   a dot at some position.  This  test  should  draw  a
different box  and if the test reads back each dot that the box is made up  of
then the test passes.

Function fourteen handles writing characters to the screen  and is similar  to
the functions describe above which handle  characters. This test uses the same
test  pattern  as used in the  above test. If the test pattern  is  read  back
correctly then the  test passes.

The  last test of the video I/O tests the current video  state. Since it  gets
its  results from a reserved area in memory,  for storing system  information,
this is where the test was  performed. Most applications use this data area to
get  system  parameters. If this area is not identical and maintained to  that
of  an IBM machine then compatability might prove to be a problem.  This  test
first  saves  the  current values and replaces them  with   test  values.  The
function is executed to see if it returns the  test values and if it does then
the test passes. When the test  finishes, it will restore the current values.


Interrupt 11 - Equipment Determination
--------------------------------------
There  are  some software packages that can determine the type   of  equipment
your  system  is using. One of the most obvious  reasons for this  is  that  a
program  which  displays graphics will  not work so well if  your  monitor  is
monochrome.  So  the program  will look to see what type of  monitor  you  are
using  and execute  it's code to handle a monochrome monitor. That way if  the
program is not dependent on using graphics, it will still  operate.

When  you turn on your PC, a set of built in diagnostics are  run  to  quickly
test the condition of your system. The  diagnostics must know what to test. It
reads the switch settings  you set on the motherboard for the type of monitor,
amount  of  memory, etc. and stores those settings in a system data  area.  If
your  program requires this information then you would execute  an   interrupt
11. This interrupt reads the settings from the data  area rather than from the
actual  switch settings on the  motherboard. Since most programs will  extract
the  switch   settings from the system data area, this is where the  test  was
performed.

The test first of all saves the current switch settings  stored in the  system
data area. It then replaces this value with  a test value. An interrupt 11  is
executed  to  find out if it  returned the test value. If so,  then  the  test
passes.  After  the  test has finished, the current switch settings  value  is
restored   back to the system data area. You could actually fool your   system
by changing the switch settings value in this data area.

Interrupt 11 returns the switch setting value in the AX  register. Each of the
bits in this register indicate the  following:

     bit 0 - indicates diskette drives on the system
     bit 1 - not used
     bit 3,2 - planar ram size
               (00 = 16K, 01 = 32K, 10 = 48K, 11 = 64K)
     bit 5,4 - initial video mode
               00 = unused
               01 = 40 x 25 black/white using a color card
               10 = 80 x 25 black/white using a color card
               11 = 80 x 25 black/white using a monochrome card
     bit 7,6 - number of diskette drives if bit 0 set
               (00 = 1, 01 = 2, 10 = 3, 11 = 4)
     bit 8 - not used
     bit 11,10,9 - number of RS-232 ports
     bit 12 - game input/output port installed
     bit 13 - not used
     bit 15,14 - number of printer ports
               (00 = 1, 01 = 2, 10 = 3, 11 = 4)


Interrupt 12 - Memory Size Determination
----------------------------------------
When  you  purchase  a  software  program,  it  usually  will  state  in   the
documentation  the amount of memory the program requires to run  successfully.
If  you have tried running a program which requires more memory than you  have
available  then you might get  the message "INSUFFICIENT MEMORY". The  program
most likely has  used interrupt 12 to first look at the amount of memory  your
system has available before trying to load the main program.  This will  avoid
the possibility of crashing your system and  leaving you in frustration as  to
what went wrong.

The  memory  size is determined when your system is powered  on or  when  your
system is booted up. In the system data area  there is a place which keeps the
amount  of  memory your system has  installed. This  determination  is  stored
there.  When  an   interrupt 12 is executed, it reads  this  value.  What  the
interrupt returns is the number of contiguous 1K blocks of  memory.

The  test  saves the current memory size and replaces it with  a  test  value.
Then an interrupt 12 is executed to see if it  returns the test value. If  the
test  value is returned then the  test has passed. After the test is  complete
the current memory  size is restored.


Interrupt 13 - Diskette Drive Interface
---------------------------------------
The  low  level  software interface between your diskette  drive   and  system
memory  is the ROM-BIOS interrupt 13. It handles the  most basic operation  of
moving data between your program and the  diskette. This interrupt is made  up
of  six basic functions  (reset the drive, getting the status of  the  drive's
operation,   reading  data, writing data, verifying data, and  formatting  the
diskette). DOS is very much dependent upon this interrupt.

Since  DOS depends on this interrupt to function properly you  can do some  of
your  own  testing by loading and executing a  program, writing  data  to  the
diskette, and formatting a diskette.  This will cover all six of the functions
listed  above.  If you  can perform these type of  functions,  without  errors
being   generated, then you have successfully tested this interrupt and   know
whether  compatibility  is a problem. You would also want to  try  and  use  a
program off of a diskette that was formatted and  setup on an IBM-PC or  known
compatible system.

The  interrupt  13 test consists of first placing a formatted,   double  sided
diskette into drive A with, better yet, some  information stored on it.  Since
a majority of the diskette  drives around now are double sided, this test will
test  both   sides of the diskette only. Once the diskette is  in  place  then
press  any  key to continue. The test begins by reseting the  drive.  Then  it
does a series of read/write tests and gets the  drive's status for both  sides
of the disk, on all forty tracks.

If  an error occurs, then an error message will be displayed   indicating  the
type  of failure. The error messages are based on  the error codes  listed  in
ROM-BIOS. If one of the tests fail  they are retried two more times to  verify
the error. DOS does a  better job of determining errors since that is what  it
was   designed to do. You may then proceed with the testing of the   remaining
tracks by pressing any key.

After  all forty tracks have been tested then the next test,  verification  of
data,  is  executed. To exercise the movement of  the heads also  ,  the  test
begins on the outside track, track  zero, then moves to the inside, back  out,
back in, until the  center track is reached and tested. Errors are handled  in
the  same way as the previous read/write tests.

Displayed  on the screen, while the test is running, is a  status  line  which
shows  you the drive being tested, the current  track, the head or  side,  the
starting sector and the number of  sectors involved in the test. This test  is
performed  on drive A,  drive zero, only and works with an entire track,  nine
sectors, at  a time. When the verify test is running you can watch the  drives
head  movement by looking at the current track it is on. After  the  test  has
finished you will see the test pass or fail message.  If just one error occurs
then the whole test is considered a  failure.


Interrupt 14 - Async Communications
-----------------------------------
While  the  ROM BIOS provides support for the serial ports,  most  programmers
requiring the use of these ports routinely bypass BIOS and work directly  with
the  hardware.  This is due to the fact that BIOS support for these  ports  is
minimal, at best.

The  ROM BIOS specifically provides four support services to the  asynchronous
ports:initialize  port, send a character from port, receive a  character  from
port and return status of com port.  Most communications programs will utilize
only  service 0 (initialize port) since interrupt driven routines,  which  are
not  directly  supported  under BIOS, are the  preferred  method  of  handling
incoming data.

For  this  reason, this test will run through diagnostics of service  0  only.
Various baud rates are initialized using BIOS.  This diagnostic then goes into
the UART chip itself to ascertain that the correct timing parameters were sent
from BIOS.

This test will display the various baud rates set along with the number  which
was  found in the divisor latch.  If they correspond with the  correct  value,
the test will pass.

This test will only be performed on COM 1.


Interrupt 16 - Keyboard
-----------------------
There are actually two different interrupts used to support the keyboard.  One
interrupt (interrupt 9) is used primarily for low level support of the  serial
transmissions  from the keyboard.  This interrupt is not generally invoked  by
user written software.

The other keyboard interrupt, which is often referred to as the "read keyboard
support",  is interrupt 16.  This is the keyboard interrupt accessed  by  most
user software programs.

As you could imagine, interrupt 16 could not function properly if interrupt  9
failed to perform its duties.  For this reason, BIOSTEST concerned itself with
interrupt 16.  Interrupt 9 is not directly tested by the validation program.

Under  interrupt type 16 there are three services available.  Service 0  reads
the next character entered into the keyboard and returns the code and its scan
code in the CPU registers.

Service  1 is invoked simply to tell us whether or not a key has been  entered
and  is  waiting in the keyboard buffer for processing.   Finally,  service  2
returns the status of the shift keys.

In order to test these services, information was placed into the ROM BIOS data
area.  Since the interrupt itself uses the data area to store information from
the  keyboard,  simple  memory manipulations are  performed  which  trick  the
keyboard  into  thinking that keys were pressed which,  in  reality,  weren't.
This enables us to check the ROM BIOS without addressing the physical keyboard
itself.

For  example, by adding a character into the keyboard buffer and changing  one
simple  pointer, the BIOS thinks that a key is waiting to be processed.   When
service  0 is subsequently called, it should return indicating a character  is
waiting.


Interrupt 17 - Parallel Printer Port
------------------------------------
Just  as in the case with the serial port, the parallel port is  supported  by
ROM  BIOS even though the device itself is not part of the motherboard.   This
means  that the system may support a device that is not even attached  to  the
system.

This  interrupt  contains three separate service routines.   Service  0  sends
characters  out the port one at a time to the printer.  Service 1 is  used  to
intialize the printer port and service 2 returns the printer status.

BIOSTEST  primarily  invokes  these routines.  It is up  to  the  operator  to
determine  whether or not the hardware is responding correctly.  For  example,
under  service  0  a  test pattern of printable characters  is  sent  out  the
parallel  port using interrupt 17.  To ascertain the correctness of the  call,
it is necessary to visually examine the output.

Service  1  merely initializes the port.  The only testing performed  on  this
service  is to examine the return code for inconsistencies after the  call  is
made.

Service 2, which returns the printer status, is easily verified by  performing
such  tricks  as taking the printer offline and then invoking  the  test.   If
working properly, BIOSTEST will indicate the condition to you.


Interrupt 18 - Invoke ROM-BASIC
-------------------------------
If  you don't have a fixed disk attached to your system, chances are  at  some
time  or another you booted up your system without a disk in the  drive.   The
result  was  that  the  machine finally enters  ROM-BASIC.   Entry  into  this
firmware version of Basic is made possible by interrupt 18.

I do not know of any clone that has Basic installed in ROM.  Microsoft wrote a
generic Basic language for clones which emulates IBM's ROM-BASIC however it is
a software only version of the language.  I'm referring to GWBASIC, of course.

For  completness,  however, BIOSTEST includes this test.  When  this  test  is
performed, an interrupt 18 is invoked which, on an IBM, should call up the ROM
resident version of Basic.

Do  not  expect this test to perform correctly on clones.  It  is  even  quite
possible that the machine may totally hose up when this call is made.


Interrupt 19 - Boot Strap Loader
--------------------------------
As  soon as the computer is turned on, ROM BIOS begins initializing  the  data
area  and  performing  diagnostic tests.  At the conclusion  of  these  tests,
control is turned over to the boot strap loader via interrupt 19.

This  routine  will simple invoke the interrupt 19 code.  When  this  happens,
your  computer should simple perform a complete reboot as would occur had  you
just turned your system on.

Interestingly enough, not all systems seem to respond this interrupt the same.
In particular, hard disk based systems will sometimes 'hang' when this test is
performed.   In  general, however, if your system comes up from  a  power  off
condition, the system should be considered ok.  This test is optional and  not
a  true  gage of compatibility.  It was included in BIOSTEST for the  sake  of
completness.


Interrupt 1A - Time of Day
--------------------------
Around 6:30 every morning, we all feel as though our lives are controlled by a
clock.  Well, we have at least one thing in common with a computer!

In the case of the PC, the second hand of the clock is advanced  approximately
18.2  times  every  second.  For you techies out  there,  the  strange  timing
interval is the result of a 1.2 mHz clock divided with a counter by 65536.

At  each advance, a register is incremented.  Determining the actual  time  is
therefor a matter of transforming this count into something more meaningful by
us  mortals.  ROM BIOS doesn't give us the upper level support to do  this;  a
service request under DOS interrupt 21 does, however.

What  ROM  BIOS does give us, however, is the ability to  read  the  so-called
clock and to set the clock.  These facilities fall under interrupt 1A services
0 and 1 respectively.

This  test  will read the hardware registers and then perform a bios  call  to
read the registers.  If they are identical, the test passes.

The second test performs just the opposite; a new value is set into the clock.
Once done, the hardware is examined to see if the call was successful.  Should
the registers differ, a failure warning will be issued.


Printout of ROM BIOS Data Area
------------------------------
ROM BIOS is contained on non-volatile memory.  As such, it does not change, it
need  not be reloaded every time the system is powered up an can operate  much
faster than the volatile memory chips affectionately referred to as RAM.

This is all well and good, but in order to operate certain variables that  are
used  by ROM BIOS must be able to change.  To accomodate this, a certain  area
of  RAM memory was set aside specifically for ROM BIOS support.  This area  is
called the ROM BIOS data area.

There  is a wealth of information stored within these areas.  As a  matter  of
fact,  it  is very common for software packages to examine  certain  locations
within this area for information pertinent to the operation of the program.

If  you  were to examine a technical manual which lists the  actual  ROM  BIOS
(such  as the IBM Technical Reference Manual), each variable in this area  has
been  assigned a label.  This procedure produces a hardcopy listing of all  of
the  data located within this data area and displays it along with its  actual
name as it appears within the tech manual.

This utility is very useful for comparing certain values contained within  the
data  area  from  those  of the real thing.  In order  to  get  the  printout,
however, a printer must be attaced to your system.


The Romdate Utility
-------------------
Hidden  deep  within  the  recesses  of most ROM  BIOS  are  three  fields  of
information  which you might find of interest.  These fields include the  type
computer system, the date of the ROM BIOS and the copyright notice.

The  field  containing the type of computer is important  since  many  machine
specific programs examine that memory location in order to determine the  host
computers  configuration.   Rather than return a  meaningless  code,  BIOSTEST
returns the type system identified by the system code.

Another  location within the ROM BIOS has historically been used to provide  a
date stamp for the ROM BIOS itself.  BIOSTEST will display this date.

Finally, a third location yields an ASCII string which consists of a copyright
notice.  This is really quite interesting (and important, as well).  There are
some  software packages that specifically test this area in order to find  the
three  magic  characters "IBM".  This was supposedly done to  prevent  certain
software from running on clones.

In order to maintain compatibility, software houses producing ROM BIOS decided
to install their own copyright notice which also contains the magical letters.
Some are quite humorous and may range from "IBM compatible" to "This is not an
IBM...".

This utility will print the first 60 or so ASCII characters found in the  area
traditionally reserved for such purposes.


The Romcheck Utility
--------------------
ROM  BIOS  is actually nothing more than a collection of  software  procedures
which  have been stored inside the computer non-volatile memory.  Software  of
this nature is referred to as "firmware".

Many  systems contain other devices not directly supported by either  the  ROM
BIOS  or  DOS.   Two such examples that are most common  are  the  fixed  disk
extension  to  interrupt  13 and the Enhanced Graphics  Adapter  extension  to
interrupt  10.   In  order to provide support for  these  devices,  the  cards
themselves contain either ROMS or EPROMS containing the firmware necessary  to
support that device.

During  a power on self test, the ROM BIOS tests certain areas of  memory  for
these ROMS and, if located, pass control to these programs.  The programs,  in
turn,  create the necessary hooks into the operating system which  enable  the
device to function.

This utility will scan the computers memory from C000:0000 up to F400:0000  in
search of these ROMS.  Should a ROM be found, its address will be displayed on
the screen.

The  most  common ROM will be found at address C800:0000.  This  ROM  provides
support  for the fixed disk.  EGA cards, on the other hand, will generally  be
found at C000:0000.


Conclusion
----------
The  program  BIOSTEST  is an attempt on our part to provide  a  standard  and
meaningful test to ascertain a PC clones compatibility to its predecessor, the
IBM PC.

In  developing  our  test, we tried to  simulate,  wherever  possible,  actual
situations where the ROM BIOS would or could be invoked.  Our tests are simple
yet quite through.

There is, of course, the possibility that an unknown bug or glitch in the  ROM
BIOS  could  go  undetected by BIOSTEST.  To  remove  this  possibility  would
require  programming effort in excess of that used to originally develope  the
BIOS itself!

Quite frankly, there are few systems in the market today whose ROM BIOS is not
compatible.   Our program will help to identify the small minority of  systems
containing a flawed ROM BIOS.