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POC VERSION TWO

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BigDumbDinosaur

Post subject: Re: POC Version 2

Posted: Mon Oct 01, 2012 7:27 pm

Joined: Thu May 28, 2009 9:46 pm
Posts: 8479
Location: Midwestern USA

GARTHWILSON wrote:

Maybe it was just down for a hiccup. Try again. I didn't have any trouble. Looks interesting.

Just tried it again. The site doesn't respond to SeaMonkey, Firefox or Internet Exploder.

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GARTHWILSON

Post subject: Re: POC Version 2

Posted: Mon Oct 01, 2012 7:33 pm

Joined: Fri Aug 30, 2002 1:09 am
Posts: 8538
Location: Southern California

Strange-- I just tried again and still no problem, with firefox running under Unbuntu Linux.

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BigEd

Post subject: Re: POC Version 2

Posted: Mon Oct 01, 2012 7:46 pm

Joined: Thu Dec 11, 2008 1:28 pm
Posts: 10976
Location: England

You should know about
http://www.downforeveryoneorjustme.com/

Cheers
Ed

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BigDumbDinosaur

Post subject: Re: POC Version 2

Posted: Tue Oct 02, 2012 5:51 am

Joined: Thu May 28, 2009 9:46 pm
Posts: 8479
Location: Midwestern USA

BigEd wrote:

You should know about
http://www.downforeveryoneorjustme.com/

Cheers
Ed

Yes, I familiar with it. It turns out the website wanted to do something with javascript that I have blocked on all our office PCs. I relaxed the setting, browsed to the page and looked at the product. What it is is a terminal that uses a PC keyboard and VGA monitor. It's not suitable for my application. However, thanks for the reference.

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Dr Jefyll

Post subject: Re: POC Version 2

Posted: Tue Oct 02, 2012 12:49 pm

Joined: Fri Dec 11, 2009 3:50 pm
Posts: 3367
Location: Ontario, Canada

BigDumbDinosaur wrote:

What it is is a terminal that uses a PC keyboard and VGA monitor.

Sounds as if there's been a misunderstanding of some kind. dottech.org has a description of DownForEveryoneOrJustMe.com along the following lines:

"It is happened to the best of us: we load up the computer to visit our favorite website and instead of being greeted with the familiar homepage, we get a 404 or connection error message. Before the withdrawal symptoms set in, it is always nice to know if the reason you can't access the website is because you have a connection problem and you can fix it or because your favorite website truly is down and it is out of your control."

The topic is relevant since, eariler in the thread, problems were mentioned with accessing brielcomputers.com

-- Jeff

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Last edited by Dr Jefyll on Tue Oct 02, 2012 1:03 pm, edited 1 time in total.

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BitWise

Post subject: Re: POC Version 2

Posted: Tue Oct 02, 2012 1:01 pm

Joined: Tue Mar 02, 2004 8:55 am
Posts: 996
Location: Berkshire, UK

Here's another keyboard/VGA solution with a simple interface

http://microvga.com/

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Open Source Projects - https://github.com/andrew-jacobs

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rwiker

Post subject: Re: POC Version 2

Posted: Tue Oct 02, 2012 3:02 pm

Joined: Thu Mar 03, 2011 5:56 pm
Posts: 284

BigDumbDinosaur wrote:

BigEd wrote:

You should know about
http://www.downforeveryoneorjustme.com/

Cheers
Ed

Yes, it is a way of getting an old-fashioned terminal using current (more or less) parts. It costs about $20 more than the other option you were looking at, but can be used without having to modify your own design. Alternatively, it might be possible to make something similar as part of the POCv2.

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Dr Jefyll

Post subject: Re: POC Version 2

Posted: Tue Oct 02, 2012 3:25 pm

Joined: Fri Dec 11, 2009 3:50 pm
Posts: 3367
Location: Ontario, Canada

Maybe I'm the one who's got the misunderstanding. What has http://www.downforeveryoneorjustme.com/ got to do with terminals? It doesn't seem like the same subject Ed was referring to. But the matter of an inaccessible web site seems seems sensible and in context.

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https://laughtonelectronics.com/Arcana/ ... mmary.html

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BigEd

Post subject: Re: POC Version 2

Posted: Tue Oct 02, 2012 6:14 pm

Joined: Thu Dec 11, 2008 1:28 pm
Posts: 10976
Location: England

Hi Jeff
I think 'it' shifted from: referring to the website, to: referring to the product (Briel's "PockeTerm" terminal computer)
The PockeTerm is a glass teletype: see http://www.retrothing.com/2009/07/the-b ... eterm.html - $70 as a kit, using a Propeller for the controller.
Cheers
Ed

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BigDumbDinosaur

Post subject: Re: POC Version 2

Posted: Tue Oct 02, 2012 7:10 pm

Joined: Thu May 28, 2009 9:46 pm
Posts: 8479
Location: Midwestern USA

BigEd wrote:

None of those "solutions" would be a solution. I already have terminals, which I don't want to have to continue to use. My plan is to embed the console hardware into the system. The process can be accomplished with an Atmel AVR and bus transceiver for the keyboard (a modified form of Daryl's design), and a Picasso VGA module for the monitor. The required software to run the console is not complicated and in the case of driving the video, uses about 80 percent of what I have already written and tested in POC V1. The only other required ingredients would be the PS/2 keyboard (or possibly a WYSE ASCII keyboard, which has the same on-board controller as that used in many PC keyboards) and a standard VGA video monitor.

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BigDumbDinosaur

Post subject: Re: POC Version 2

Posted: Mon Oct 08, 2012 6:22 pm

Joined: Thu May 28, 2009 9:46 pm
Posts: 8479
Location: Midwestern USA

Hmmm...the Picaso VGA module doesn't have support for a hardware cursor. A cursor is essential in an application that supports/requires interactive input. Doing one in software, such as was done in the Commodore 64, would be laborious.

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BigDumbDinosaur

Post subject: Re: POC Version 2

Posted: Wed Oct 10, 2012 5:19 am

Joined: Thu May 28, 2009 9:46 pm
Posts: 8479
Location: Midwestern USA

BigDumbDinosaur wrote:

Aaah, the plot further thickens. Aside from not having a hardware cursor, the Picaso also has no facilities for partial screen clearing or clearing to the end of a line. This device is starting to look less attractive. The partial screen clearing and clearing to the end of a line could be simulated in software through a somewhat cumbersome process of using a graphic function to overlay text with a solid block of the same color as the background. It's not too code-intensive, but really shouldn't be necessary, given the general intelligence of the device. Also, I would be concerned about how fast the display would be using such a technique.

A flashing cursor would be very laborious to implement and would have to be interrupt-driven, using a technique that was used with the Commodore video interface controllers (VIC) used in the VIC-20, C-64 and C-128 (40 column display). In those machines, the IRQ handler had to keep track of where the "cursor" (there was no real cursor in the VIC) was located and the character that was under it. Periodically the IRQ handler would switch the character from normal video to reverse video and then later reverse the process. The actual change to the character was accomplished by changing the character code (not PETSCII) in video RAM.

The same technique would be necessary with the Picaso and would be complicated by the fact that the module, being a serial device, must be buffered and interrupt-driven. Having both a foreground and interrupt-driven process writing on the same buffer would pose some synchronization problems. Complicating matters, the Picaso does not have the ability to display reverse video characters. Reverse video would have to be simulated by interchanging foreground and background colors at the cursor location. A static cursor would be a bit simpler but not much, since the basic problem of normal vs. reverse video remains.

The idea of using this VGA module was to equip POC with a built-in console (using a PS/2 keyboard, as well as a VGA monitor). However, the inability of the Picaso module to support to very basic and necessary functions in a console display has me reconsidering.

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Last edited by BigDumbDinosaur on Wed Oct 10, 2012 5:01 pm, edited 1 time in total.

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BigEd

Post subject: Re: POC Version 2

Posted: Wed Oct 10, 2012 6:29 am

Joined: Thu Dec 11, 2008 1:28 pm
Posts: 10976
Location: England

I think you're too harsh - although of course it may not be the device for you - because the features it does provide, at that cost and convenience, could easily outweigh the drawbacks you mention. I'm surprised you are fazed by the cursor problem, when you're up for writing a filing system!
Cheers
Ed

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BigDumbDinosaur

Post subject: Re: POC Version 2

Posted: Wed Oct 10, 2012 5:43 pm

Joined: Thu May 28, 2009 9:46 pm
Posts: 8479
Location: Midwestern USA

BigEd wrote:

Not fazed but concerned about what it would take to produce a cursor.

The cursor problem stems from a fundamental capability that the Picaso lacks. Consider how it is done in the Commodore 64, whose VIC chip lacks a hardware cursor.

The C-64 has 1K of RAM that is the display RAM for the VIC, with a one-for-one correspondence between a byte in display RAM and a visible location on the screen. When you print a character to the screen that character is converted to a screen code and the resulting value written to display RAM at a location determined by the current cursor position. Also, the display kernel (screen editor) code writes the current color value in a parallel block of RAM to set the character's color. The display functions then update the cursor position so the cursor "moves" to the next position on the screen.

Now here's where it gets tricky: if the cursor is moved to an arbitrary position (e.g., by using the kernel PLOT function) then the display kernel has to know what character is in the new cursor position. The reason is that the visible cursor is generated by rendering the character under the cursor in reverse video, which is accomplished by temporarily substituting a different character code for the one that is in display RAM at the cursor position. If the screen kernel didn't know what the character code was at that location to begin with it couldn't reverse it. The entire process is contingent on the screen kernel being able to read what is at any given screen location and alter it to produce reverse video. This cannot be done with the Picaso because there is no function that can retrieve the character that was previously written to an arbitrary screen location (there is X-Y coordinate setting available for each character when written).

In order to support a true cursor, that is, one that can be moved to any screen location and will appear as a reverse video version of the character at that location, I'd have to maintain a set of maps in RAM, one containing codes corresponding to each character on the screen and another containing codes corresponding to the attributes of each character. On an 80 x 24 display, that would mean 3840 bytes of RAM devoted to the display maps, plus (presumably zero page) bytes to keep track of the cursor position. Further compounding the problem, if the screen is scrolled, the entire display map has to be shifted to reflect the changes. The code required to manage the display now becomes quite large, no small consideration when stuffing it into a ROM.

Now, if the cursor is to flash (which is essential with CRT monitors to avoid burn-in problems) the IRQ has to repeatedly switch the cursor on and off, which entails writing to the Picaso each time the cursor state is to be changed. The Picaso, being a serial device, is driven by IRQs which read from the TxD buffer and write to the device when it is ready. In order for the IRQ to change the cursor state it would have to also write to the Picaso, creating an obvious conflict with foreground activity that may also be producing screen output.

So it has nothing to do with being fazed by the problem, merely a reluctance to commit so much in the way of system resources to generating a cursor.

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BigEd

Post subject: Re: POC Version 2

Posted: Wed Oct 10, 2012 6:22 pm

Joined: Thu Dec 11, 2008 1:28 pm
Posts: 10976
Location: England

Well, it's clearly built as a graphics display. A nice mail asking for an enhancement might be the thing.

But as for the cursor, isn't this what XOR cursors were invented for? You don't need to map the damage, you just re-apply.

Cheers
Ed

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