Issue 8 discussions...

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Dave
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Re: Issue 8 discussions...

Postby Dave » Fri Jun 28, 2019 4:29 pm

Deadlines. I suck at them! UltimIDE will be here in 2014!

All I can do is tell you my progress, share the decisions (some hard, some easy) and let you figure out for yourselves when it'll be a thing.


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Re: Issue 8 discussions...

Postby Derek_Stewart » Fri Jul 12, 2019 10:55 pm

Hi,

What isthe status of the Issue 8 board?


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Derek
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Dave
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Re: Issue 8 discussions...

Postby Dave » Sun Jul 14, 2019 7:56 pm

Things are going slow right now.

I'm investigating a couple of low level decisions about the video system. I'm not really happy with any of the options that have been presented to me, or any I have devised myself. I'm still noodling it out.


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Dave
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Re: Issue 8 discussions...

Postby Dave » Thu Aug 01, 2019 7:37 pm

And summer arrived. Nasta always goes radio silent all summer, and I have summer stuff to do!

See you when the nights get shorter!


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Re: Issue 8 discussions...

Postby Nasta » Fri Aug 02, 2019 8:57 pm

Not silent, just very busy until Oct. 1st - yesterday. Lots of deadlines before most suppliers go to collective holidays.


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Dave
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Re: Issue 8 discussions...

Postby Dave » Fri Aug 02, 2019 10:39 pm

AKA fun times. :D

It’s a cycle you’ve followed for years. I follow a similar cycle.

I will be away for a whole year in 2021 o 2022. Just setting expectations.


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Re: Issue 8 discussions...

Postby Derek_Stewart » Sat Aug 03, 2019 3:03 pm

Hi Dave,

So does mean no Issue 8 board then...?


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Derek
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Re: Issue 8 discussions...

Postby Nasta » Sat Aug 03, 2019 7:14 pm

Well, the schematic has more or less been fixed for a while.
One thing that has been done is that the original video RAM (first 64k) has been replaced by real dual port RAM, which uncouples CPU and video accesses completely, there is never any contention or slowdown.
This also makes it possible to access the screen RAM much faster with proper hardware, to a point where it becomes possible to get a true QL display on a regular VGA screen (also the CPU side can be accessed much faster if needed).

The plan was then to move the video sub-system onto a small daughterboard. The actual dual port RAM stays on the ISS8 board.
The video sub-system can then in principle be many things, one of which is the original 8301, which would of course be used to produce the exact same display as usual, as a first option, and for people who want to keep exact original functionality, including compatibility with original QL (compatible) monitors and TVs.
The first alternative, to be introduced next, would be hardware that does the exact QL video, but on a VGA compatible monitor - reason being, ISS8 is supposed to be as close to the original machine, but we have a serious problem getting compatible monitors, plus, what we can get is old and prone to failure.

The underlying problem is that the video RAM data port that is used to generate video, should ideally be kept 16-bit wide (Although the rest of the machine still uses an 8-bit data bus), and the address bus non-multiplexed, because it seriously simplifies replacement video hardware. This requires more pins on any sort of daughterboard that carries the video hardware, which complicates things - and indeed having a daughterboard does by itself.
On the other hand, leaving it at the 8301 is wasting a huge opportunity - while it may be possible to make a replacement that interfaces through the 8301 socket, the required logic becomes almost 2x more complex, and it would have to come as there is still that undeniable thing of 8301s failing, eventually being in short supply, and as i said already, monitors being in even shorter supply well before the 8301 becomes a real issue.
Sorting out this conundrum from the standpoint of physical execution of the board is currently the biggest issue.

HOWEVER! Note this does not imply introducing higher resolutions or more colors. Because video RAM is limited, little would be gained a the cost of breaking compatibility, so any such functionality belongs to the (expanded :) ) expansion port -remember, ISS8 is supposed to look externally as close to a regular QL as possible, with some (considerable) extra options should the user decide to enable them.


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Re: Issue 8 discussions...

Postby tcat » Tue Aug 13, 2019 5:30 pm

Hi,

Rereading the topic now and again. I wish to ask, what makes it different to hook 8302 on CPU data bus as with Iss#6 vs RAM bus in Iss#5, is there any performance gain?

Many thanks
Tomas


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Re: Issue 8 discussions...

Postby mk79 » Wed Aug 14, 2019 12:33 pm

tcat wrote:Rereading the topic now and again. I wish to ask, what makes it different to hook 8302 on CPU data bus as with Iss#6 vs RAM bus in Iss#5, is there any performance gain?
The RAM side of the bus is often occupied with RAM refresh, so communication to 8302 stalls every time the RAM is being refreshed. You don't have this problem when it's on the CPU side of the bus. So yes, it's faster, but it also has the advantage that the communication is continuous during an access cycle. I don't think you'll measure any or much difference in actual QL speed.



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