FOTH on a Raspberry Pi

[Andy Doz]

Would this be possible?

I can get linux to work on PC's, but I have little other experience.

I can code, but not in anything remotely suitable (a language called TSL, bespoke to stuff my company makes).

Any thoughts?

[julie_m]

The problem is that the Raspberry Pi graphics "chipset" is highly proprietary, and will require some pretty severe reverse-engineering of the binary firmware to add new timings for new video modes.

Which being said, no-one should ever underestimate what can be done by a few million Freds in a few million Sheds, especially with a wiki. So, do hold your breath!

[paulsherwin]

You can run a standard Linux distribution reasonably easily, but FOTH relies on manipulating the analogue outputs on the VGA interface to produce 405 line signals. The Raspberry Pi doesn't have this interface.

I'm far from being an expert on this though.

[julie_m]

All FOTH does is run a suitable PC graphics card with "non-standard" timings, so as to match 405 line broadcasts. (It doesn't work with every graphics card on the market, because it relies on the graphics card not sanity-checking your timings; or at least not considering a scan rate of 10.125 kHz to be insane.) The X window system is specifically designed to allow user-defined "modelines" to support almost any scan rate and sync pulse polarity, so you can in theory use any old monitor.

The Pi does not have an explicit VGA port, but its composite video output contains pre-summed luminance and sync signals (also colour difference signals; which we aren't interested in here, as 405 is strictly a mono standard).

The obstacle is persuading its graphics subsystem to run the "weirdy" timings and the documentation necessary to do so is not available to mere mortals

[Andy Doz]

Pity, I thought the whole raspberry pi thing was designed to be open source. I suppose the manufacturer of the GPU doesn't necessarily subscribe to that though.

[mhennessy]

This is covered on the FAQ:

What hardware documentation will be available?

Broadcom don’t release a full datasheet for the BCM2835, which is the chip at the heart of the Raspberry Pi. We will release a datasheet for the SoC which will cover the hardware exposed on the Raspi board e.g. the GPIOs. We will also release a board schematic later on.

But I want documentation for <hardware X>!

Other documentation may be released in future but this will be at the Foundation’s discretion.

But I demand the documentation for the chip. Give it to me!

To get the full SoC documentation you would need to sign an NDA with Broadcom, who make the chip and sell it to us. But you would also need to provide a business model and estimate of how many chips you are going to sell.

But perhaps if enough people ask the foundation this question, they might consider helping out somehow. I could imagine that they'd think it was a cool use of a Pi...

Mark

[paulsherwin]

Broadcom don't have a good track record when it comes to releasing technical specs.

[Sean Williams]

Er have a contact at Broadcom will have a word with him.

[dominicbeesley]

Originally Posted by ajs_derby

(also colour difference signals; which we aren't interested in here, as 405 is strictly a mono standard)

News to me! There was the 405/NTSC that was broadcast on a test basis in the 50's and 60's.

I doubt that 405 will be possible without getting into the GPU chipset, the device drivers for this seem to be a closely guarded secret, which for me is the single most dissappointing aspect, second to rubbish documentation, of this otherwise excellent project!

I've just looked at the documentation for the firmware configuration and the options are:
sdtv_mode=0 Normal NTSC
sdtv_mode=1 Japanese version of NTSC – no pedestal
sdtv_mode=2 Normal PAL
sdtv_mode=3 Brazilian version of PAL – 525/60 rather than 625/50, different subcarrier


Having said all that it _might_ be possible to ask the foundation to have a look at adding a 405 line mode as they do make changes to the firmware quite often...I doubt this request would get top-billing. I'm guessing it should be either quite easy (set timings and memory layout) or impossible (timings etc are hardware limited).

As an aside I have written a simple C test program that output an NBTV testcard from the sound output...

[julie_m]

Oh, I know about the tests of NTSC on 405, but nothing serious ever came of this. And a good job too, it would most probably have put people off the idea of colour TV altogether! At least with PAL, things on the screen come out looking something like the same colour as they are in real life

[cmjones01]

I wouldn't be surprised if the TV output was restricted in hardware to 'standard' modes anyway, given the complexity of generating the video signal digitally. There may be more mileage in reprogramming the HDMI output, which is likely to have more flexible timings, then converting it to analogue. That could even be done by the back door: I don't know whether the Raspberry Pi takes notice of the monitor DDC information, but it certainly has an I2C bus connected to the right place on the connector. What if someone was to connect something to that which indicated that a monitor supported a 405-line interlaced video mode?

Chris

[Tractorfan]

Hi,
What please is FOTH? I might learn something if I knew what it was!
Cheers, Pete

[cmjones01]

Originally Posted by Tractorfan

What please is FOTH?

http://www.g1jbg.co.uk/fothtv.htm

[julie_m]

FotHTV is our very own Kat Manton's amazing project to generate arbitrary TV standards (especially "obsolete" ones such as 405 and 819 lines) using a standard PC. The name is taken from "The Fools on the Hill", a disparaging nickname once applied to some of the early television pioneers, by those who never expected it to work.

[cheerfulcharlie]

Originally Posted by ajs_derby

Oh, I know about the tests of NTSC on 405, but nothing serious ever came of this. And a good job too -- it would most probably have put people off the idea of colour TV altogether! At least with PAL, things on the screen come out looking something like the same colour as they are in real life

Not as bad as you might think maybe?

http://www.youtube.com/watch?v=uAkNGdBTDQ4

[dominicbeesley]

It didn't seem to bother the Americans or Japanese for the best part of 60 years! I have to say it works _almost_ as well as pall you just have to twiddle a control occasionally. However most folks sit and happily watch modern flat screens with off hue over saturated colours on modern tellys that have no excuse...

Back on topic I think I might have to work out a request for putting in a 405 mode for the PI...

[Tractorfan]

Hi,

Thanks to all for explaining what FOTH is. I was thinking it was a technical term like: Field Oversampling Timebase Humdinger, or something like that. The "Fools on the Hill" never entered my head. I enjoyed that programme too.

I think I'll stick to my tape recorders and wind-up gramophone!

Cheers,
Pete

[emeritus]

When this thread started, I thought it was a typo for the obsolete computer language FORTH, as used on the Jupiter Ace computer.

[julie_m]

Originally Posted by emeritus

When this thread started, I thought it was a typo for the obsolete computer language FORTH, as used on the Jupiter Ace computer.

Well, there's bound to be an Open Source FORTH implementation that would run on it.

And, of course, whenever you print anything in Linux, the app creates PostScript; a Forth-like typesetting language built into many laser printers. This is then converted to the printer's native format by a compatibility layer called GhostScript; a PostScript interpreter with a modular architecture, allowing plugins to be written for various printers.

But we're drifting here .....

[audion_1908]

Hi, what about using the raspberry pi with an HDMI to VGA adapter and running it with a custom HDMI mode, and with the use of an rf modulator you would have 405 line tv? down side would be the cost of the HDMI to VGA adapter.

Custom HDMI modes for the raspberry
http://www.raspberrypi.org/phpBB3/viewtopic.php?f=29&t=24679