Default display parameters for DSI


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by thecottonsilk » Sat May 05, 2012 11:54 am
Its verify interesting to note the DSI availability on RPi.

Is DSI streaming enabled by default? or we need to set some display parameter ?

Also can anybody throw some light on default set of display timing parameters for DSI on RPi..
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by mahjongg » Sat May 05, 2012 12:05 pm
DSI is NOT working at the moment, as no driver has been written for it yet. the RpiF has announced they will come with an LCD for the DSI connector, and they will probably release patches for the kernel driver to support it, but that doesn't men other (DSI) LCD's will also be supported, or any documentation. But well see about that when it happens.
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by Gert van Loo » Sat May 05, 2012 1:34 pm
I asked about DSI from our local expert. In contrast to a camera, it is not too dificult to setup the DSI interface to talk to a display. But it still requires the GPU to do all the work so we need to wait for a Linux-talks-to-GPU-talks-to-DSI drivers.

Also it does not make sense to do this until somebody finds a BIG stack of common available DSI screens in the price range of Rapberry-Pi customers.

Maybe we just need to point all display vendors to this post and see if anybody is interested in the potential of in selling a few hundred thousand screens :-)
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by ceteras » Thu May 10, 2012 9:11 am
I find this whole DSI/CSI connector story a little awkward, after all has been done to minimize costs and keep features to a minim that would make sense for the Foundation, these two connectors were placed and routed then soldered in the final version without a use in sight anytime soon. An I2S header would have made a lot more sense.

@Gert, I think it does make sense to provide the community with the needed support for DSI even before a mass-produced cheap display is found.

Many of us already have a DSI display in some older phone. I have an nokia 5800 for instance (also I have the display pinouts and a soldering iron). If I had the software support for initializing the DSI port, I would work to get my display running, then post the results for anyone interested to make their own. Many others would do that too and a pool of knowledge on the matter could develop.

Some phone replacement screens can be found for as little as 10pounds.

All you need is actually just one display, to test your software, then share it for others to try to configure it for other displays.

You know the saying: "if you build it, they will come"! :)
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by jamesh » Thu May 10, 2012 9:15 am
Indeed. We just need to find the time to find a screen, build an interface board, and write the software to interface to the DSI driver to Linux.

It will happen. It just needs time. After all the board has ONLY just started getting in to the hands of customers.
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by rew » Thu May 10, 2012 11:24 am
ceteras said:

Many of us already have a DSI display in some older phone. I have an nokia 5800 for instance (also I have the display pinouts and a soldering iron).

Hi Ceteras, I too have a '5800 display lying around. I'm still using the 5800 that's still around it. I'd order a replacement 5800 screen if I knew the 5800 display was DSI with the proper number of channels. Do you know if this is the case?
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by ceteras » Thu May 10, 2012 12:47 pm
Good question, actually I'm not that sure anymore.

The 5800 screen has two interfaces, according to the schematic.

One is LoSSI (low speed screen interface), 4 pin : serial data in/out, clock, chip select, reset.

The other one is HiSSI, DSI style, one clock pair and two data pairs (only one data pair used in the schematic).

If this HiSSI is DSI or not, it remains to be seen.

The schematic can be found on the internet.
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by rew » Fri May 11, 2012 7:22 am
The chip has two data lanes. The display has two datalanes. The text labels for the bus attachments are there, there is a decoupling inductor on the otherwise "unused" data pair.

I'm guessing there are two lines missing in the schematics we have.

(On the other hand, it could be that this was a very late modification to the schematics before it went "hardware").
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by thecottonsilk » Fri May 11, 2012 9:19 am
JamesH said:


Indeed. We just need to find the time to find a screen, build an interface board, and write the software to interface to the DSI driver to Linux.


I think, development of DSI driver for Linux should get started in parallel based on a couple of widely available resolution displays (1024x600, 1366x768, etc., need not be this resolution only, just gave an example to start with)
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by Neil » Fri May 11, 2012 9:19 am
rew said:


…. there is a decoupling inductor on the otherwise "unused" data pair.


Classic!

Oh, and they're not an unused data pair, the connector is clearly only for 2-lane DSI, although the 2835 can support 4-lane as well.  A shame there's no I2C to read out the EDID but as long as you know which display you're hooking up that shouldn't be a problem.
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by jamesh » Fri May 11, 2012 10:48 am
thecottonsilk said:


JamesH said:


Indeed. We just need to find the time to find a screen, build an interface board, and write the software to interface to the DSI driver to Linux.


I think, development of DSI driver for Linux should get started in parallel based on a couple of widely available resolution displays (1024x600, 1366x768, etc., need not be this resolution only, just gave an example to start with)


Parallelism assumes you have an extra processor....
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by thecottonsilk » Fri May 11, 2012 11:06 am
JamesH said:


Parallelism assumes you have an extra processor....


I didn't mean that processor parallelism..I meant we should get started with driver development sooner. If porting of existing DSI driver/s is good enough, then may be its a worth shot..
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by Paul Webster » Fri May 11, 2012 12:00 pm

I didn"t mean that processor parallelism..


I suspect that JamesH was referring to a human processor.
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by cheery » Fri May 11, 2012 12:28 pm
I think we should try pick some really good DSI display and implement support for that. Here"s some requirements:


  • 90dpi or more

  • Comes in matte surface (factor in at choices)

  • Good&fast color response

  • Capacitive touch (factor in at choices, though may not be really necessary)

  • Square, regular pixel layout and none of that idiotic power-saving non-square layouts. (http://www.extremetech.com/com.....microscope)


You might want it cheap. But I must say it's equally good idea to poke your eyes out and therefore save all the money entirely on the display, as it is to make trade offs about the display quality.
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by jamesh » Fri May 11, 2012 12:42 pm
I'm thinking (having looked at the current DSI drivers available on the VC4), that we should be able to remotely set up parameters in the driver via a linux library, that way most DSI screens could be used - just program the parameters up from the host. We actually have a driver that works a bit like that already - just need the Linux library to vchiq stuff + some GPU side code to handle passing the input to the driver to be written.

So, it's not a huge job, but it's still a job without someone to do it.
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by cheery » Fri May 11, 2012 2:57 pm
I'm willing to help on this if it's still on the table when I'll get my RPi.
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by rew » Sat May 12, 2012 8:08 pm
The problem, I'm afraid, is that James is hinting at that there is GPU code involved. Thus only broadcom engineers like Gert, James and Dom are able to work on that. (And within that population of a few Broadcom engineers, many are not experienced in writing that GPU code, so only one or two people with too little time remain).
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by disneysw » Mon May 14, 2012 11:47 pm
I have a few observations about the DSI interface, which I am hope others can qualify.
It appears that all that is required to drive DSI display are one or more data lanes. There is no requirement for a separate I2C EDID bus as the primary lane is bi-directional and acts as a command and control bus - correct?

Looking at the schematic for a Nokia N8 it uses two lanes plus two GPIO for backlight control which signal a DB1754 LED backlight controller. None of the GPIO was brought out to the DSI connector, so the simplest way to control a backlight is to jumper the connector to some of the GPIO pins?

Google Nokia_N8-00_RM-596_schematics_v2.0byfirdous.pdf and view http://www.parts4repair.com/product_ima ... 8_zoom.jpg for more info.


Even if I connected the display, it seems there is no signal on the DSI pins so I guess there is nothing can be done with the DSI interface at this point?
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by dengulebaron » Sat May 19, 2012 7:18 pm
Neil wrote:A shame there's no I2C to read out the EDID but as long as you know which display you're hooking up that shouldn't be a problem.


But the RPi does provide two I2C buses or are you referring to the displays?
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by Norefall » Sat Jun 23, 2012 9:38 am
@Gert, any news on when this driver is coming?

rPi have many volunteers who can take over if you at least have made the GPU side of the code. I think this should be given priority over the camera module/driver.
Since rPI do not have VGA, this is the only solution that provides low-cost display with acceptable quality (and ultra low-power).
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by jamesh » Sat Jun 23, 2012 9:43 am
I'm afraid no-one has looked at this yet.

I think the camera module is more important TBH. I think more people want camera than display, since you can already plug in a scree of some description.
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by cheery » Sat Jun 23, 2012 3:36 pm
I'd want both... but meh.
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by AndrewS » Sat Jun 23, 2012 11:17 pm
cheery wrote:I'd want both... but meh.

Couple of Raspis, couple of cameras, couple of small screens... http://www.tinmith.net/backpack.htm :D
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by Gert van Loo » Sun Jun 24, 2012 3:27 pm
I love that!
With a raspberry-Pi we could probably do that all with the helmet alone.
Ok, we might need a small battery pack at the girth as the weight on the element would be a bit uncomfortable.
.
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by sumith » Fri Sep 14, 2012 6:02 am
Hi ,

I am just started using raspberry pi. I found a DSI connector in the board. For my project I want to use a touchscreen display.

1.Can I use this DSI connector for touchscreen display? If yes,could you tell me how?
2. If it is not possible,how I can connect touchscreen display to raspberry pi?

Please reply me as soon as possible.

Thank you
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