Had no trouble reading the specnext group

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Re: Had no trouble reading the specnext group

Post by Alcoholics Anonymous » Mon Mar 11, 2019 3:25 pm

PiyoTaro wrote:
Mon Mar 11, 2019 8:08 am
Since it seems that the article of "co-processor" to which David Ball was posted on February 26th (during this period) is not interested, so I would like to repost this post.
https://www.facebook.com/groups/specnex ... %22O%22%7D
*Contents: An introduction article of "PiTubeDirect" Pi second processor project on GitHub. Author hoglet67. https://github.com/hoglet67/PiTubeDirect/wiki
I don't understand why people seem so interested in this. Why would you want to slow down the pi to emulate another cpu when you can run it as a native arm machine?

I can understand it on a bbc machine as it had this tube thing from the beginning to allow another cpu to be used in the machine. You had to have a z80 to run cp/m to be taken seriously as a business machine. So taking this tube thing to its logical conclusion you can put really fast versions of these cpus on it by emulating them in a pi.

But on a next what would be the purpose of having a 100MHz z80 emulated on a pi when you could be running the pi as a 1GHz Arm??

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Re: Had no trouble reading the specnext group

Post by varmfskii » Mon Mar 11, 2019 4:34 pm

People don't generally understand how the device actually operates. They visualize what would happen if the Z80 in Spectrum could be run at 100MHz (or more) without all the additional issues. They see everything running 32 times as fast. This isn't helped by the fact that well behaved programs on the Beeb using the tube a;most look this way due to the ability to use "OS" hooks to call I/O operations.

Of course the situation on the ZX Spectrum Next is nothing like this. You are actually left with the reality that The (like the tube) the co-processor interface is (or will be) merely a bidirectional communication interface between the Next and the Pi. There are many things that have the potential to make good use of this, but few if any of them involve emulating a Z80 on the Pi side.
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Re: Had no trouble reading the specnext group

Post by Alcoholics Anonymous » Mon Mar 11, 2019 5:06 pm

Yes I suppose that's the case.

The pi0 is barely able to keep up with a 2MHz interface to the 6502 in the bbc in the pitube mainly due to interrupt latency. They switched to using the GPU to make the interface reliably work. In this arrangement the pi is running bare metal software (ie all it does is emulate a cpu in a small memory space and monitor the interface to the bbc acting as terminal).

The tkpie that victor was using a long time ago as interface to the pi had the pi again running bare metal code so that all it did was watch the z80 interface to sniff out writes to ula memory so it could construct a ula video signal on the pi's hdmi port. This was a little flaky apparently.

Anyway neither makes good use of the pi. The pitube is doing much more by having it emulate the entire machine on the pi with only io and video writes reflected back to the bbc terminal. But I don't think the pi0 will be able to emulate a zx next at any reasonable speed so that wouldn't be an option here unless the GPU can be harnassed to handle most of the video work.

Allowing the pi to run full speed and mostly independently so that it is not synchronized to the z80 bus does allow it to act as more things, including a native arm machine running linux. There are some good ideas that have been suggested but it's probably premature to mention them because if they don't come about people may be disappointed (I know I would be :P )

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Re: Had no trouble reading the specnext group

Post by SpectrumOldi » Tue Mar 12, 2019 8:13 am

Let it run Retropie?
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Re: Had no trouble reading the specnext group / out of the title of this thread

Post by PiyoTaro » Sun Mar 24, 2019 12:16 pm

On March 13, there was a report that there was a global connection failure at FB. However, the "public group" was viewed normally.

Since I did not explain "Tube" of "BBC Micro" (I was mistaken for BBCMicro as a Spectrum compatible machine while fighting with Google translation), I corrected the previous statement.
And the reply to me is out of the title of this thread. I rebuilt a new thread.

Note: that ZXSpectrum compatible machines use "CPU socket" instead of "edge connector" as a system extension method such as DMA and AY. It seems that I wanted to write this.

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Re: Had no trouble reading the specnext group

Post by Alcoholics Anonymous » Thu Mar 28, 2019 5:05 pm

For the next itself, I don't think it makes sense to use the pitube thing from the bbc. Finding a way to use the pi at its full potential is really what we're after. There are a few ideas on this but the first step is likely to be a uart connection so that the pi and next can communicate quickly and asynchronously. This will open up the possibility of using the pi as a resource and to gain access to a linux install as a terminal.

A bbc core with the pitube feature is very likely going to appear, especially given that a first untested stab at it has already been written by hoglett. I can see some things will need to be fixed up but the bits are there. The first cased release is probably getting a minimal linux install for the pi but later on, there will have to be some figuring out to find a way to boot the pi up in the way needed by a specific next core. For the bbc, a bare metal program that implements pitube. For the next itself, something else, etc.

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