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Raspberry Pi Model "C" without DSI and CSI?

morgaine

I found those DSI and CSI connectors puzzling from the start.

 

The Pi already provides two display options as standard, HDMI and composite video.  Although some people will be interested in a 3rd option such as a MIPI Alliance display board attached to the DSI connector, it seems very peculiar to be increasing the BOM cost of every Pi manufactured by incorporating this 15-pin DSI connector into the design.  After all, it is certain to be only of minority interest as a result of the 2 other options being available as standard.

 

The CSI-2 interface is also a 15-pin MIPI Alliance connector, and it's another peculiar choice to find on every Pi.  After all, webcams are universal, low cost, and attach through USB which Pi already supports, so only a very small minority are likely to be interested in purchasing a dedicated CSI camera board.  And yet, as with the DSI connector, this extra burden has been added to the BOM cost of every Pi, even the $25 model A.

 

It doesn't seem to make much sense on cost, to my way of thinking, and there is yet another non-monetary "cost" to consider --- adding those two 15-pin MIPI connectors must have contributed PCB layout/routing difficulties as well, and has probably meant that other useful signals were not brought out.

 

Given the above, it's worth speculating what another Raspberry Pi model could be like, if those two connectors were crossed off the list for a hypothetical new Raspberry Pi Model C.

 

The simplest case just removes those two connectors and replaces them with nothing.  This could be enough to warrant a new price point for the Model C, below the $25 mark, particularly if the tracks and the corresponding vias are removed along with the connectors.  In the quest for a lower price point, perhaps even the current GPIO headers and corresponding tracks could be considered optional as well..

 

A much more interesting case would be to remove DSI and CSI but add another row of GPIO-type headers on the opposite edge of the board to the current 26-pin P1.  This would provide the physical support for a daughterboard which many people have suggested would be useful.  I suspect that the SoC has plenty of other interesting signals that could be routed to such a second row of headers.

 

 

Morgaine.

  • I believe Gert has joined this forum today, so maybe we can get some insight

    into such design decisions.

  • in reply to Former Member

    That's cool.  I think Pi engineers have a problem on the other site.  For some reason they feel like they're under permanent attack and so they answer defensively, which really makes no sense in an engineering discussion which isn't about people.  Here the interest is much more clearly about volts and amps.

  • I agree about USB.  I have to keep reminding myself when thinking about integration that it's just Linux with USB host, so lots of peripherals have the potential to work.  One advantage though for the CSI connector may be that it allows the camera to be handled by the GPU's powerful encoding capabilities (if made accessible by RPi team).  In general though, I agree that more standard I/O headers would be nice in a future version, especially if symmetrical like on the BeagleBone.

  • in reply to fustini

    I'm totally undewhelmed by any facility that can only be provided by the Foundation and Broadcom.  It isn't fit well with open educational goals in my view, but instead creates a closed educational monopoly.

  • in reply to morgaine

    Hello Morgaine,

    You raise a very interesting point, which motivates this question: Since the RPi concept has uncovered a large market, then what is to stop others from designing an open HW board that competes with the RPi?  Where is it written that an RPi class board needs to use a Broadcom SoC or be sanctioned by the RPi foundation?  I think the current order backlog for the RPi indicates an opportunity for other enterprising "capitalists" to enter the market with designs that are more open and will generate more economic opportunities for both HW daughter card designers and SW deverlopers.

    Allen H.

  • in reply to Former Member

    Allen, that's exactly what I've been wondering ever since the Pi began to approach reality and actual launch.

     

    The other ARM licensees can't be happy that their competitor Broadcom is getting all the limelight and appears to be well positioned into creating a monopoly in education.  I fully expected a response from one or more of them (especially TI and ST) in the same price niche as Pi, because even when there is very little profit on the basic board, you still make money from accessories and add-ons and there is a big PR / exposure benefit from it too.

     

    So far, the only well known response to Pi has been from Olimex, who are well known for being lightning fast in coming up with new board designs.  Unfortunately their existing low-end ARM Linux board doesn't compete in the same price niche as Pi so it's not going to make it big in the Pi space (they're mainly targetting open hardware fans).  This surprised me, because they are very good at creating low-price ARM boards --- for example I have this very nice Cortex-M3 board for under 18 pounds UK -- http://www.olimex.com/dev/olimexino-stm32.html

     

    So yes, I agree strongly.  The opportunities for competition are there, and the need for it is clear to avoid Broadcom's monopoly over education which would be a very bad thing, and there is even a bullet point to be gained -- more open hardware, more documentation, less proprietary rubbish, and as you very nicely put it, "more economic opportunities for both HW daughter card designers and SW deverlopers."

     

    I agree entirely.

     

    Morgaine.

  • I think what you are thinking of is a alpha borad witch has a HDMI port and a USB port wich it is powerd from and takes input from utilising a powerd usb hub. would that be what you are thinking of by any chance?

  • in reply to Former Member

    No, the hypothetical Model C board would just be a model A with DSI/CSI connectors and routing removed for further BOM cost and price reductions.  The same could be done with model B.  Adding rows of GPIO headers runs up costs in the opposite direction, so I'm really talking about a range of possible models.