Uncreative Labs

Joined: 19 Apr 2012 Posts: 9

I have lost the utilitiy for my XT "speed.com" due to floppy disk bad sectors! Help! This utility is my only means of putting the machine in "turbo" (8 Mhz) mode.

Please, if you have it or know where I can get it, let me know. I have searched Google exhaustively to no avail.

Joined: 03 Feb 2006 Posts: 488 Location: pennsylvanai

there may be a jumper
or a keyboard sequence
searh for that.

Joined: 19 Apr 2012 Posts: 9

wdegroot wrote:

there may be a jumper
or a keyboard sequence
searh for that.

I thought about that. I tried before but I'll try again.

Thanks for replying.

Joined: 19 Apr 2012 Posts: 9

I've found several schematics of the system and am now positive there is no hardware control switch for the speed. I can only guess that the "speed.com" utility alters the values in the timer through a port in order to change the clock speed.... sigh.

Joined: 03 Feb 2006 Posts: 488 Location: pennsylvanai

Ok sent me an email to an address where I can send the programs

wdegroot@ptd.net

use "turbo xt "in the title

Joined: 19 Apr 2012 Posts: 9

wdegroot wrote:

Ok sent me an email to an address where I can send the programs

wdegroot@ptd.net

use "turbo xt "in the title

Done.

Joined: 19 Apr 2012 Posts: 9

This morning through an amazing stroke of luck, I have found the file. I have now put the "turbo" back into my XT and all is well.

Joined: 03 Feb 2006 Posts: 488 Location: pennsylvanai

read this
It runs at 4.77 MHz by default, but switches supposedly to 8 Mhz Turbo mode with a "Ctrl Alt -" key combination (there is a 24 MHz TTL oscillator in the board).
The design seems similar to other Taiwanese XT clone boards, but this has 3 PAL ICs: one is at bottom center near the RAM sockets and the other two are located in the left, between the two Crystal oscillators. From one of these two PALs there are two wires soldered in the bottom side that also enable Turbo mode when shorted.

The problem is that benchmark results report slower clock rates or less performance than expected (Checkit for example says that the 8088 is running at 6 MHz). Without turbo engaged the performance is the expected at 4.77 MHz.

I have tried different bioses with the same result.
Any idea or advice to discover how is wrong?

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March 3rd, 2011, 09:46 AM #2
per
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Perhaps the system clock is changed too when you trigger turbo mode? I would believe that the system and CPU have separate crystalls, but if it's a really cheap board, it may not be the case.

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Obsolete:Commodore A500 ( ~1990 ), IBM PS/2 model 70/386 type 8570-161 ( 1991 ), Atari Lynx II ( ~1992 ), Generic Intel 486SX PC ( ~1993 ), AT/T Globalyst Pentium w/FDIV bug MB ( 1994 ), Compaq 486DX4 laptop ( ~1995 ).

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March 3rd, 2011, 01:53 PM #3
mikey99
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That looks very similar to the XT clone board I have. Mine has an IBM Basic burned
into those ROM chips.

I haven't tried running a benchmark on this but I'll try sometime over the next few days
as I do currently have this board installed in a case . EDIT: I dont think mine is a Turbo board
though, because it has a V20 installed :

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March 3rd, 2011, 02:00 PM #4
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Quote Originally Posted by per View Post
Perhaps the system clock is changed too when you trigger turbo mode? I would believe that the system and CPU have separate crystalls, but if it's a really cheap board, it may not be the case.
They do have different crystals--the 8254 continues to use 1.19 MHz as its clock regardless of turbo setting.

This board was an ERSO-standard design with lots of little tweaks. I have yet another version that looks more like Mikey's board, but there are 3 DIP packages just above the switches.

Again, the trick here is to figure out what the frequency coming into the CPU clock is. If it's 6MHz, you look upstream and see how an 18MHz signal could be derived from a 24MHz source. If it's 8MHz, then you look to see who's adding the wait states.

Just for yucks, have you tried a different CPU in the socket?

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March 3rd, 2011, 11:54 PM #5
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Yes, I tried with a 8088 in plastic package (the original 8088-2 has ceramic package) and the result is the same. How can I see what is adding wait states?

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March 4th, 2011, 02:56 AM #6
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Most likely suspect is RAM timings. The ram is probably down at the system bus speed and the 8088 with it's 8 bit bus is then spending a lot of time waiting.

It boils down to how assembly is executed on the 8088. Thanks to the 8 bit bus that let it be built with cheaper componants it takes a minimum of 2 clocks to read a word-sized parcel of data, and the pre-fetch will always grab a word... Real world this works out to about 4.13 clocks to read the average x86 instruction from memory thanks to the DRAM refresh interval.

Now, if the instructions being executed take more than that 4 clocks to execute, the next word can be grabbed while it's being processed -- the problem is that if the opcodes take less than four clocks -- inc, dec or bitwise operators for example -- multiples of those in a row end up 'rounded up' waiting for the data to be retrieved from RAM. Micheal Abrash called these types of effects the "cycle eaters".

http://www.phatcode.net/res/224/file...h04/04-01.html

Which is why a benchmark might only report a 30-40% speed increase despite the CPU's clock speed being doubled. The tandy 1000's 7.14 mhz clock speed sees similar issues waiting on memory which is why really long instructions (like jmp, mul, etc) see the speed boost but short instructions (shl ax,1; inc ax) actually end up some 80-90% of the time the same speed as they do at 4.77mhz, as the CPU is sitting there with it's thumb up it's backside waiting on RAM for the next instruction.

Which is why the 8088 is often a very poor candidate for higher clock speeds unless the RAM can keep up. At really high clock speeds (12mhz+) you often end up with little if any speed bonus over 10mhz as the code is executing inside the CPU so fast, it's outpacing the prefetch queue unless you are on a design that uses more modern ram with a more robust caching controller. (see why many of the rare 20mhz XT class boards used 70ns 30 pin SIPPs or SIMMs)

Last edited by deathshadow; March 4th, 2011 at 03:02 AM.

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March 5th, 2011, 01:11 AM #7
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Thank you for the link, I found it very interesting.

Here are some benchmarks:

LandMark6:
at 4.77 MHz: CPU Clock: 4.77 MHz, performs like a 2.49 MHz AT
at 8.00 MHz: CPU Clock: 7.997 MHz, performs like a 3.78 MHz AT

Norton Utilities 4.5 System Information:
at 4.77 MHz: CPU 1.0
at 8.00 MHz: CPU 1.4

Checkit 3.0

at 4.77 MHz: CPU Clock: 4.77 MHz, 344 Dhrystones / 6.6K Whetstones
at 8.00 MHz: CPU Clock: 6.14 MHz, 558 Dhrystones / 10.6K Whetstones

Do you find this results normal?

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March 5th, 2011, 08:03 AM #8
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A quick check with Norton 4.5 on my own "Turbo XT" (this one) gives an SI of 1.7 at 8MHz (that's with an 8088 installed).

So it looks as if yours probably has some memory speed issues. Not all "Turbo XTs" were created equal.

But given the similarity of mine to yours and the look that yours is somewhat more modern, I've got to wonder about those wire jumpers on yours.

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March 6th, 2011, 11:06 PM #9
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So the board is performing worse than expected at 8 MHz... now that it is confirme, I will trace the 24 MHz oscillator path to the 8284. I suspect the two PALs will be in the middle of this path, at least physically they are placed in the board between oscillator and the 8284.

The two wires have one side soldered to one of the PALs, in the back side of the PCB. The other side is soldered to a 2 pin header. Shorting this header makes the board switch to Turbo mode, the same as pressing "Ctrl Alt -" key combination.

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March 7th, 2011, 12:26 AM #10
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If we think perofrmance-wise, each clock cycle usually takes 4 clocks. When 4 clocks is expected at 8MHz and one extra waitstate is added, the performance will resemble 6.4MHz.

On the other hand, 24MHz/4 = 6MHz too.

Current systems owned by me:
Vintage:IBM PC/XT submodel 087 ( 1983 ), [Kon]tiki-100 rev. C (1983), Compaq Portable I ( 1984 ), IBM PC/XT submodel 078 ( 1985 ), IBM PC/XT286 ( ~1986 ), 3x Nintendo Entertainement Systems ( 1987 ).
Obsolete:Commodore A500 ( ~1990 ), IBM PS/2 model 70/386 type 8570-161 ( 1991 ), Atari Lynx II ( ~1992 ), Generic Intel 486SX PC ( ~1993 ), AT/T Globalyst Pentium w/FDIV bug MB ( 1994 ), Compaq 486DX4 laptop ( ~1995 ).

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Joined: 02 Oct 2004 Posts: 594 Location: Western NC

Walter, if you post something copied from another site, it's best to give credit (somewhere at the start of the post) to that site. We don't want to get "nuked" for "web-plagiarism". Please edit the above post to do so...

Joined: 03 Feb 2006 Posts: 488 Location: pennsylvanai

http://www.vintage-computer.com/vcforum/showthread.php?24210-Poor-performance-in-a-Turbo-XT-motherboard

realy tra I only intended to copy and paste the key sequense
not the whole darn thing
maybe someone here can ask
I am registed there but somehwo it is not working

He reports the files I sent him do not work\
but he found the proper files
HOW
I think he said it was LUVK

I did several searches and could not find the util
It was in the midst of my broer craching and 3 re-installs

Joined: 19 Apr 2012 Posts: 9

I've tried every Ctrl-Alt key combo possible to no avail. I really think the speed.com utility is the only way. I am busy disassembling the code to figure out how it works. I will post the results when I have them. So far I'm still at the part where it parses the command line arguments, I have to skim through the string tables as it's a COM type executable without a separate DATA segment.

BTW: if anyone is curious where I found the program - as well as a couple more I never had to begin with, here is the link

http://www.welook4things.com/sub_laser_xt_docs.html