AlanCox
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Re: VGA

Sat Nov 12, 2011 6:30 pm

Yeah my monitors are all without HDMI, ditto my TV and I don't think its atypical right now. But in 2 years time ?

PAL I think is best avoided - its a nightmare getting all the TV frequency stuff screened even in a boxed product and the regulations and testing for radio emissions are really tight unless you have enough money to get someone to make it abroad and lie about their testing on the forms (which clearly happens from some products I've see)

Composite is an odd one - I can't help feeling its a nostalgia connector ;)

Other way to do VGA and DVI output is to use a USB plug in display. Linux supports the displaylink devices. You won't easilly be able to get 3D from it (because the PI 3D is closed so you can't set them up together I suspect) but it should give a usable display. Costs more than the PI though 8)

jeremy
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Re: VGA

Sat Nov 12, 2011 11:54 pm

All of this has been said. The horse is dead and we should not continue to beat it.

Never reply to a topic with 8 pages of posts unless you are willing to read all of the existing posts to verify that your point hasn't already been made once or twice (or in this case, ten times.)

Please do not reply, as this message is being sent from an unattended mailbox. ;)

doveman
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Re: VGA

Wed Dec 07, 2011 4:42 pm

My own thread about this was locked pretty sharpish (sorry, I couldn't find anything by searching for VGA), so I'll have to respond here. I quite understand the reasons for the Pi not having VGA but as ways to add it in future are being considered, it seems reasonable to offer my thoughts.

Firstly, obarthelemy suggested there's a bunch of DVI LCD monitors in the $10-$40 range available on ebay, which may be true in the US but in the UK it seems you're unlikely to find much below £30, which more than doubles the total overlay per Pi.

ebay UK DVI LCD's under £40

I can see how in the developing world, where they might only have a CRT TV and no monitors, and perhaps don't sit around watching TV as much as we do in the west (meaning that the kids can get the time in on the Pi) the composite out will be brilliant though.

I wonder if a model with VGA does become a possibility, whether it will be able to make it like ATI graphics cards, which allow the use of a simple cable to convert the RGB into a TV-SCART compatible format like so https://sites.google.com/site/joecontra ... art-basics (I've recently done this to build an HTPC for someone who only has a CRT TV and no prospect of this changing any time soon). It does require the use of custom timings, but I imagine that's something that could be set as an option on the Pi.

The reason I suggest this is because then the VGA port could also drive SCART TVs, with a much better picture than composite (which could be dropped to save a few pennies), but then again I think SCART is a Euro-only thing, so this wouldn't be much use in the developing world :?

doveman
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Re: VGA

Wed Dec 07, 2011 5:08 pm

I really hope this thread doesn't get locked (at least not without directing me to a thread about this that will remain unlocked) as it might have been discussed a lot, but that doesn't mean we should prevent further sensible discussion of it, particularly as the team have said they're considering the possibility of a future model with VGA.

Of course, if the team were to say that they've decided it's not possible, then it would be fair enough to stamp on any further discussion as it would be a waste of time (unless someone comes up with a brilliant idea they might not have considered, but that seems unlikely).

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Burngate
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Re: VGA

Wed Dec 07, 2011 5:18 pm

There are several threads which have been worn thread-bare, and this is another.
The concensus on the forum appears to be: Yes we'd like it, and No we won't get it.
The Foundation (it's more than a team!) have explained their reasoning, very patiently.

Other similar are:
Why no mounting holes?
Why don't all the connectors come out at one edge?
Why no wi-fi?
Why is the GPU not open-source?

Often the answer has been "use the search", to which the reply is "Why can't I search for VGA?" and the answer to that is just "cos. So there"

jamesh
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Re: VGA

Wed Dec 07, 2011 5:47 pm

Quote from doveman on December 7, 2011, 17:08
I really hope this thread doesn't get locked (at least not without directing me to a thread about this that will remain unlocked) as it might have been discussed a lot, but that doesn't mean we should prevent further sensible discussion of it, particularly as the team have said they're considering the possibility of a future model with VGA.

Of course, if the team were to say that they've decided it's not possible, then it would be fair enough to stamp on any further discussion as it would be a waste of time (unless someone comes up with a brilliant idea they might not have considered, but that seems unlikely).

If you read through the rest of this thread I think you will find that many of your points have already been raised and discussed. If you still have any more questions after that, you can use this thread to post questions/comments.
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doveman
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Re: VGA

Wed Dec 07, 2011 6:03 pm

Quote from Burngate on December 7, 2011, 17:18
There are several threads which have been worn thread-bare, and this is another.
The concensus on the forum appears to be: Yes we'd like it, and No we won't get it.
The Foundation (it's more than a team!) have explained their reasoning, very patiently.

I've never questioned their reasoning and I'm only going by what Eben is quoted as saying here

"I agree that the lack of VGA output is a very significant problem with the device, particularly in school environments, where (at least in the UK) there are often labs full of old analog monitors. Although we can’t afford to add chips to the baseline device to support it, we’re investigating three routes to add VGA compatibility in the future:

Supporting monochrome output directly using our single-channel analog TV interface.
Bridging from the HDMI/DVI output to VGA using an add-on board or “smart cable”.
Bridging from the onboard MIPI DSI interface in the same way.

This is right at the top of our follow-on project list, once the main boards are out of the door."

If that's rubbish, don't blame me. If it's still being looked at, it seems reasonable to make suggestions and discuss it.

doveman
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Re: VGA

Wed Dec 07, 2011 6:07 pm

If you read through the rest of this thread I think you will find that many of your points have already been raised and discussed. If you still have any more questions after that, you can use this thread to post questions/comments.

I did take the time to read through this entire thread before posting and didn't consider that my points had been discussed (at least not how I put them) before, or I wouldn't have bothered posting.

I don't suppose I'll have anything else to add, but thanks for confirming that this thread is the appropriate place to do so if I do.

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Jessie
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Re: VGA

Wed Dec 07, 2011 7:15 pm

Anologue devices makes a bunch of ICs to do ADC and DAC with various video sources they usually run from $10 to $20 a peice. By the time you design a board and buy connectors it would cost about as much as the Pi.

Alternitively, someone with a big head on their shoulders could use the GPIO pins to generate VGA via a resistor-ladder DAC and a software driver. It would eat up tons of CPU time but it would be almost free.

I ditched VGA years agao, you don't realize how piss poor it looks until you get used to sitting in front of a nice monitor with DVI or HDMI and then go back and take a glimpse at a computer running off a VGA port. I fully understand there are cases for the VGA port, like places where it would cost too much to buy even a used monitor with DVI, but some people here are just crying because they want their $35 computer to have everything and that just isn't going to happen.

bradburts
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Re: VGA

Wed Dec 07, 2011 8:03 pm

You can get a HDMI to VGA cable for $5.
A DAC / GPIO solution would be hard work, you would need EDIT: (calculator typo!) 300KHz x 3 DAC updates for one frame.
I don't see the interfaces with the bandwidth available to do it from the Pi at reasonable frame rates. Text and juddering VNC style GUI is all that could be done manually I suspect.
I am told that the Pi also has an LCD interface. LCD screens can be found for not much or cannibalised. Hopefully the LCD driver will be modable to allow users to add more screens.

EDIT:
Its probably been covered already but after a little more reading it appears that the cable convertor don't work well, or at all.
Should be possible to do something with LCD interface (if programmable) or HDMI to parallel and then the three DACs..... IDK never used DACs above 1KHz so don't know what they cost at 1Mhz or more but more like $1 for 2 channels @ 100Khz.
EDIT: The first DAC I found was 20Mhz, $1.5 @ 1000 http://www.analog.com/en/digit.....oduct.html. Not gonna be <$10. Resistors sounds better.
If the LCD programmable and can match Hsynchs then I think it could be done cheap.

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abishur
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Re: VGA

Wed Dec 07, 2011 10:07 pm

@doveman, don't take it too hard. You're jumping in fresh to a three week old stale coffee situation ;) It also doesn't help that the forum can't search strings of three characters or less (so it's manual searching for USB, GPU, VGA, etc thread), but seeing as how this thread has been up since August, you're in the right spot, we don't pointlessly close threads. :)

As for what you're saying, well, really there's no one disagreeing with you per se. Everyone would love to have VGA, but more than cost, the reigning issue is the fact that the SoC itself simply doesn't support VGA :( (which I think you or someone noted in your thread which was closed)

The R-Pi does recognize, as you noticed, that this is a bit of an issue, but the sad truth is that at the present moment there is no solution beyond purchase a convertor.
Dear forum: Play nice ;-)

doveman
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Re: VGA

Wed Dec 07, 2011 10:27 pm

Thanks abishur, I guess I came late to the party and started telling all the same jokes (and I didn't bring a bottle) ;)

Anyway, I appreciate it's not simple (maybe impossible) to do anything about it and it's not a case of poor decisions by the foundation, but I'll keep my ear to the ground in case an affordable solution is found :)

abingham
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Re: VGA

Thu Dec 08, 2011 1:24 am

In the US, Monoprice.com has active HDMI -> VGA + Audio converters for $40 for qty 1, $35 for Qty 50+.

http://www.monoprice.com/produ.....8;format=2

It is annoying that they cost as much as the R-Pi does, but much less than $110....

(I have no association with Monoprice other then as a satisfied customer)

hamjudo
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Re: VGA

Thu Dec 08, 2011 2:29 am

Windows users are used to the idea of one monitor, and one keyboard, per computer. I use more than one computer, so I prefer one keyboard, and a couple monitors, per person. The monitors and the keyboard are physically connected directly to the computer in front of me. Through the magic of networking, I can connect to any of the other computers on the network. Thus I don't have to get up out of my chair to use a different computer.

I didn't see any discussion of X Windows, VNC, or their ilk in this thread. This is how us old timers always used to program embedded Linux (or back in the day, Unix) systems without VGA connectors, using VGA monitors (or the technology of the day, 13W3, or worse). We would network the embedded system to whatever desktop was handy. Then connect to it over the network. If we had to use a serial port for the network, then things involving realtime video were not an option. With 100Mbit ethernet, pretty much everything just works.

Being a long time Unix/Linux user, I generally use X Windows. However, if there is a classroom filled with ancient computers running Windows 2000, and for technical or political reasons, the teacher can't boot off of live CD (lack of CD drives would be the most common technical reason), use VNC. There are versions of VNC available for ancient Windows versions back to Windows 95.

I worked for an industrial robotics company. In theory, you could connect a VGA monitor to the computer that controlled the 4 meter long robotic arm that moved the diesel engine blocks around. Assuming you didn't get killed by getting hit with an engine block, you would get fired on the spot for being inside the work area of the robot.

Javid
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Re: VGA

Thu Dec 08, 2011 3:10 am

It's really silly to expect people to spend $40 for an adapter to hook a $35 computer to the most commonly available monitors in the target environment.

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Jessie
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Re: VGA

Thu Dec 08, 2011 4:06 am

Quote from bradburts on December 7, 2011, 20:03
You can get a HDMI to VGA cable for $5.
Devices have to be built to support these cables, and most do not. Most devices require an active form of conversion from HDMI to VGA.

A DAC / GPIO solution would be hard work, you would need EDIT: (calculator typo!) 300KHz x 3 DAC updates for one frame.
If people can do it with Atmel AVRs running at 28 Mhz then it can be done with these Broadcom processors.

I don't see the interfaces with the bandwidth available to do it from the Pi at reasonable frame rates. Text and juddering VNC style GUI is all that could be done manually I suspect.



Replies in bold.

bradburts
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Re: VGA

Thu Dec 08, 2011 8:54 am

Thanks Jessie.
I figured out that the cables don't work in my edit.

You're right, a simple text monitor would be very easy. I was thinking games and colour, doh.
For programming a shell would be good enough.
So a serial link to microcontroller complete with our own RPI font table would only cost $3.
The shell would not be hard to write either.

The DAC part of my post is about transcoding HDMI. I have not looked in detail, it much easier if rows can be made to align, perhaps DSI allows this, then you don't need a row/frame buffer.
$40 seems a lot, I only got to $10 oom but I don't have HDMI or DSI experience.

jamesh
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Re: VGA

Thu Dec 08, 2011 9:03 am

Quote from Javid on December 8, 2011, 03:10
It's really silly to expect people to spend $40 for an adapter to hook a $35 computer to the most commonly available monitors in the target environment.

Why? You still have a Linux PC for $75.
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adric22
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Re: VGA

Thu Dec 08, 2011 4:46 pm

Quote from jamesh on December 8, 2011, 09:03
Why? You still have a Linux PC for $75.
That $40 could be better spent on a monitor that can accept HDMI or DVI. I mean, you can pick up used LCD monitors for that amount of money these days.

hippy
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Re: VGA

Thu Dec 08, 2011 5:42 pm

Quote from Jessie on December 8, 2011, 04:06
If people can do it with Atmel AVRs running at 28 Mhz then it can be done with these Broadcom processors.

It should be possible to bit-bang out 16 colour VGA using just six GPIO lines and while not perfect, may not be suitable for all applications, it would be acceptable in many instances and most importantly be a very simple low-cost VGA interface.

It's already been done using an SD Card interface and shouldn't, I imagine, be too difficult to port to using GPIO and copying the frame buffer out for someone who has Linux experience ...

http://downloads.qi-hardware.c.....bb/vga/web

So - who's going to be the first to port the code ?

bradburts
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Re: VGA

Thu Dec 08, 2011 7:04 pm

The code is quite simple, just shifts and catching what pops out, as you say but....

"The driver currently runs in user space (with a lot of dirty tricks) and blocks all other system activity while running"
VGA 640x480 pixel clock is around 25MHz. I don't know what the context switch latency is on an ARM these days but I bet its a little more than 40nS.

So using software only it would be VGA and nothing else, except as can be coded within the tight VGA loop. Also got VSynch and HSych intervals but not much is going to happen in them.

A text console rendered by an Atmel / PIC / whatever is very doable and would be cheap.
Could even add character mapping graphics like the old days.
I would guess that the VGA/SVGA text console would have four components to make;
1) RPI shell to serial driver, just glue really to SPI lib and shell
2) RPI GPIO protection HW, thats wip with Gert & is only needed during development.
3) Atmel driver, we have a reference design
4) Atmel board & VGA I/O, we have a reference design

Many here have pointed out RCA displays for $30 or second hand monitors for $50, so I don't think there will be many first world takers.
Its would be for third world use. Only advantage I see is that for $3 you could have a lot clearer screen than RCA for text based programming using a discarded VGA monitor.

EDIT: Or you could use the Atmel to display a GUI but refresh rates would be very slow, say few frames per second max @640x480, depending on colour depth.

doveman
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Re: VGA

Thu Dec 08, 2011 8:58 pm

Quote from bradburts on December 8, 2011, 19:04

Many here have pointed out RCA displays for $30 or second hand monitors for $50, so I don't think there will be many first world takers.
Its would be for third world use. Only advantage I see is that for $3 you could have a lot clearer screen than RCA for text based programming using a discarded VGA monitor.

You might be right, but then again I'd question what sort of quality LCD you'd got for £30 (about the cheapest on ebay.co.uk). I bought a Benq a couple of years ago that gave me a headache as the text was shimmering when scrolling, so I sent it right back and kept using my 19" CRT. I'm happy with the new £110 Dell I've just bought (which I only got as there was a £60 cashback offer. I've given the CRT to someone who can't afford to buy a LCD), but in many cases people might be having to spend £30 to get an inferior display to the CRT one they already have (or can get free), which I doubt they'll be happy to do.

Chris
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Re: VGA

Thu Dec 08, 2011 9:07 pm

Quote from adric22 on December 8, 2011, 16:46
Quote from jamesh on December 8, 2011, 09:03
Why? You still have a Linux PC for $75.
That $40 could be better spent on a monitor that can accept HDMI or DVI. I mean, you can pick up used LCD monitors for that amount of money these days.

Where, I will by 2, no 3..... seriously WHERE????

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Re: VGA

Thu Dec 08, 2011 9:15 pm

Bit bashing VGA would be a nightmare, you may be able to do it but you won't be able to do anything else at all! Of course you could always use one of the 'other' processors in the SoC to do it (there are a few, it really depends on your definition of processor!)

The best way to do this though is also the easiest... Output the VGA signal as DPI then add a DAC or resistor network if you don't care too much about more than 256 colour. You'll probably need a couple of FETs to level shift the syncs (they're 5V) but thats it...

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bradburts
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Re: VGA

Thu Dec 08, 2011 10:30 pm

Agreed, bit bashing would have to be on a secondary processor, Atmel, PIC or whatever say.

"Output the VGA signal as DPI "
I thought the same but did not get much information on DSI from wiki. Isn't the RPI DSI? There are only 15 pins. If so we would have to chop the bit stream and latch before feeding the resistors & FETs? Easy enough, never used LVDS chipsets though.
Too much hardware for me to prototype.
If you know more about the RPI hardware or thought on this design then I would be interested.

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