Should P2 boards use Mini Displayport as the video standard?
ke4pjw
Posts: 1,079
in Propeller 2
Do you guys think it would be good for P2 based boards that produce video, to standardize on Mini Displayport? As I understand it, there is no royalty. I know there are cheap cables that automatically convert to VGA or HDMI. (Purchased a MiniDP to VGA cable earlier this week for my Surface dock.) The connector is small and convenient and after the respin, the P2 should be able to produce HDMI fairly easy, right?
Just wondering aloud, waiting for by ES board to arrive
--Terry
Just wondering aloud, waiting for by ES board to arrive
--Terry
Comments
DisplayPort video signals are not the same as DVI/HDMI video signals. It doesn't make a lot of sense to me to create a non-standard device that only puts an HDMI signal onto the DisplayPort connector. It wouldn't meet the DisplayPort spec and adapters that convert a DisplayPort signal to other ports wouldn't work.
Does anyone know if there is any electrical or signalling difference between DisplayPort and HDMI? Is it merely a connector issue?
I think the LVDS signaling is 3.3v vs 5V for HDMI.
I say don't try to make a standard because that's the last thing it will be.
It's an entirely different protocol. I'm not an expert, but the DisplayPort FAQ says it uses a "packetized data structure", which is how it can support things like multi stream transport, etc. Where as HDMI is just a single video link not that different from DVI....
I just don't recommend mixing and matching signals with connectors in non-standard ways, like putting an HDMI-only signal onto a DisplayPort connector.
The DVI-I connector can carry both DVI digital video (same electrical spec as HDMI) and analog VGA, so if someone wanted to put a single video connector on a P2 board that supports both analog and digital video, that is the connector that makes the most sense....
marsman2020, you are probably correct. When I last researched this, I thought they (Display Port and HDMI) were very similar. Sounds like I am most likely mistaken.
See wiki
That suggests they all use LVDS as the transport, but it needs a dual-mode (ie a change in the card config) to change from one to the other.
So that's more than just a connector issue.
The P2 has been tested with 250MHz HDMI, and HDMI is what the Rasp Pi supports, so that seems the more natural pathway for P2 and any PCB connectors to take.
HDMI also supports Audio, not sure if P2 has managed Audio + Video yet ?
Another issue is that P2 VGA can be 1080p, whereas P2 HDMI is limited to 480p.
If we use a VGA to HDMI converter we have an unnecessary digital-analog-digital conversion, loosing quality.
If we use a standard HDMI to VGA converter, we are limited to 480p. Here is a rare cable that might be wired straight through instead of using a converter IC: https://newegg.com/Product/Product.aspx?Item=9SIA4UB7JW5355&Description=hdmi%20to%20vga%20cable&cm_re=hdmi_to_vga_cable-_-1DG-0007-000T0-_-Product
HDMI needs 8 pins. We could build a custom adapter that routes 5 to VGA, 2 for analog audio, and maybe one for composite video.
DVI-I can do both with standard off-the-shelf adapters. It's a locking connector. DVI-I shares essentially no pins between analog and digital. Just I2C, power, and ground. I don't know if bridging the analog and digital pins together would cause strange issues. It would depend how the cables or adapters were wired. If the adapter connected to only one set of pins it should be fine.
VGA and microHDMI wouldn't be much bigger than DVI-I. That might be a better bet for sharing the pins. Add a 1/8" TRRS jack for audio and composite video. That's likely to be cheaper than building a custom adapter cable.
Or use separate connectors so they can both be used at the same time. I wonder if P2 can do VGA input. Or HDMI input? Might be possible...
I would like to keep the boards as small as possible so would prefer a MicroHDMI connector. I'm fairly confident that an adapter could be made for VGA monitors that would allow the MicroHDMI cable to be used for hi res VGA and audio as well.
Forcing every P2 user to use the same "standard" or "connector" simply won't work!
Composite Video, Componet Video, VGA Video, HDMI Video, Displayport are all different, and don't forget there are other "standards" and "connector" types including "LVDS" and "DVI" etc.
Personally I have several Televisions, that range in size from 6 inches in size to 58 inches in size. These TVs have many types of inputs: Composite Video, Componet Video, VGA Video, HDMI Video and DVI video, but none have Displayport Inputs.
I also own many Computer Monitors, most of them accept one or more of the Video Types I have listed above for TVs. A few of my Computer Monitors also accept Displayport video.
Forcing analog signals through connectors designed for digital signals, and vice-versa does not work well.
My experience is that using passive adapters to adapt from say from HDMI to Mini HDMI or Micro HDMI or even DVI (without sound) works well.
Using adapters with active electronics inside is simply a no-go for many of my projects.
MHL would be a great option for minimizing space as it uses a microUSB connector. Since it multiplexes 3 channels of TDMS data onto 1 the minimum bitrate is probably 750Mbps, 3x that of DVI. Way too high for P2.
I'd like to see ATSC output. 1 pin for 1080p30 output into any TV. It should be doable when the IQ modulator is fixed. Since the data is send compressed, we could store it compressed in the P2. We'd have to because the P2 can't do MPEG encoding for HD video.
Displayport ismuch more complex to implement. The cheap cables are not actually coverters. The Intel video display chipsets can output DVI/HDMI (which are the same electrical interface) over the Displayport pins allowing a simple adapter. But that means they have to have hardware for both. That is easy when your Intel and have hundreds of millions of transistors to play with. Adding that capability is virtually free. Its much more difficult on the P2 without adding extra hardware either on die or as a separate part on the board. HDMI for right now seems a good way to go. Everything supports it and there are active adapters that can convert to DP if you really need it. In the future that may be an issue if DP completely replaces HDMI. However TVs use HDMI and typically do not use display port so there is no sign of a total replacement going on yet. By the time that happens, say in 10 years, they can probably pair it with a DP (or whatever the latest greatest whiz bang interface is) on a chiplet in the same package. There is potentially a shift coming in the manufacturing industry, where complex devices with large and varied functionalities will be built with off the shelf parts assembled together in multichip packages from commodity components. That could actually be very good for companies like Parallax. The P3 could potentially be sold as hub chiplets and cog chiplets and maybe interface chiplets. Parallax could sell devices made of perhaps 1-4 hubs connected together and anywhere from 1 to 16 4 core cog chiplets to their own customers core customers. Perhaps they could supply an interface chiplet that would be used instead of a cog chiplet to provide industry standard interconnects to other devices allowing other manufacturers to build P3 based parts with expanded functionality using off the shelf chiplets for things like video or communcations,and have it all come together as a seamless whole.
The thing is, thats just speculation. You can see the industry moving that direction. DARPA is putting a lot of money into it. Intel has released the specs on their chiplet communications buss royalty free. But who knows, the entire thing could flame out in two years, manufacturers could decide they want to use the technology to create multichip devices that are not much different than what they already sell, and in 3 years were back to the status quo. Personally ,Im not to concerned about Parallax future proofing the P2 when no one really knows what that future is going to be.
Display port is very different. I beleive its packetized. The simple passive adapters are only usable on devices that have an actually HDMI port built in and can multiplex it onto the pins for the DP.
(On the subject of the multichip packages, Parallax already has one Chip, and as such is already half way there. You should bring this up with your wife or gf. All you need are some "Chiplets" and Parallax can be an industry leader.
Even the header on the P2-ES would handle this although i wouldn't try to have an actual pcb sitting directly on the pins, but at the end of a cable if need be.