[sebhc] HDOS boot/space bar question.

Glenn Roberts gfroberts at adelphia.net
Sun Jul 30 06:10:18 CDT 2006

You are correct, the SPACE requirement is the way the HDOS boot program 
detects the BAUD rate on your terminal. On the H8 you'll hear a 200 ms tone 
and see S.P.A.C.E. spelled out on the LED's (I'm guessing the H89 just 
beeps?) as an indication that you need to hit the space bar. The code tries 
reading from the UART using different baud rate divisors until it does not 
see a "framing error". At that point it has a valid baud rate divisor. If 
the disk is not write protected it will store that 16 bit divisor back onto 
the disk (I believe at offset 5 in the first sector - 042.205). On 
subsequent boots if the code sees a non-zero divisor it will skip the 
"SPACE" code and go right to the "BOOT" prompt.

By default it will wait 60 seconds at the BOOT prompt, then auto-boot. You 
can patch this value to something less (at 044.254). Besides typing "B" for 
boot, you can also type "C" for checksum or "I" for ignore. If I'm reading 
the code properly it looks like 'C' performs a checksum on the code image 
loaded from the boot track to make sure it's not corrupt. I believe 'I' will 
cause the disk to auto-boot on subsequent boots (I'm having a problem with 
my H17 right now or I'd try these myself). From the code comments it looks 
like 'I' was added as part of HDOS-2.

The code for all of this is in the INIT program:


- Glenn

----- Original Message ----- 
From: "Mark Garlanger" <garlanger at gmail.com>
To: "sebhc" <sebhc at sebhc.org>
Sent: Saturday, July 22, 2006 12:26 PM
Subject: [sebhc] HDOS boot/space bar question.

> Does anyone know what makes HDOS decide if it needs the user to press
> space bars before booting? I heard that it was to detect the baud rate
> between the computer and terminal, but only some of my disks require
> that, even though they are all ver. 2.0. I was thinking that a bunch
> of my disk were bad since they weren't booting, until I remembered
> about the 'space bar' thing.  Also, if I remember correctly, there is
> a way to make HDOS just boot, instead of presenting the <BOOT>
> question. How can you change it?  My final question is about HDOS
> capitalizing everything. A few of my disks decide that everying must
> be capitalized, how do I change that?
> Thanks,
>   Mark
> --
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