Tee­ing up a dis­play for an embed­ded sys­tem is a little more com­plex than buy­ing a monitor.

At the core of it is one of my favor­ite say­ings, “The won­der­ful thing about stand­ards is that there are so many to choose from.”

Start­ing from the screen end of things, I want a screen that is roughly 150x90mm in size. Because I want it view­able from the side and ideally all angles, I have a strong pref­er­ence for an IPS dis­play. I found a screen that is really nice,Topfoison’s 6″ IPS dis­play.

This dis­play uses MIPI DSI for its video sig­nal, spe­cific­ally a 4 lane MIPI DSI inter­face (because stand­ards restrict choice too much many stand­ards allow incom­pat­ib­il­ity within themselves).

MIPI DSI is an inter­est­ing stand­ard, it is a mobile industry stand­ard (Mobile Industry Pro­cessor Inter­face — pro­nounced lower­case as mipi, like nbn) which essen­tially spe­cifies a num­ber of half duplex SERDES links for throw­ing video around. Many mobile phones seem to have adop­ted the stand­ard as it removes the need for a video con­verter — redu­cing part count/cost, sim­pli­fy­ing cabling and redu­cing internal EMI. The dis­play and chip man­u­fac­tur­ers have shif­ted with the mar­ket. How­ever as it is fairly new mostly it is new/expensive hard­ware with sup­port.
If you are meant to be doing some­thing else here is some fur­ther read­ing, nice over­view, detail with pretty scope pic­tures.

So, look­ing at hard­ware to plug in to this we have:

  • BananaPi M1, the board I have been plan­ning on using.
    Is not lis­ted as sup­port­ing MIPI DSI, does sup­port rel­at­ively gen­eric LVDS out­put.
    Graph­ics pro­cessor is the ARM MALI400 MP2, the newer ARM MALI cores include a dis­play con­trol­ler but I believe this wasn’t the case for the MALI400. I haven’t been able to find doc­u­ment­a­tion on what dis­play con­trol­ler All­win­ner used in the A20 chip­set.
    Some web­sites do claim that BPI has a MIPI DSI out­put, I think they are wrong and are simply assum­ing that the Rasp­berryPi look-alike video header is a function-alike video header.
  • BananaPi M2
    Uses the All­win­ner A31s (data­sheet) chip­set which does not sup­port MIPI DSI out­put.
    The All­win­ner A31 does, but it seems they removed it when plur­al­ising chip.
    The Sino­Voip web­site lists the out­put as “LVDS/RGB/CPU dis­play inter­face (DSI) for raw LCD pan­els” on the product page. How­ever the DSI gets dropped when get­ting into the detailed LCD con­nec­tion inform­a­tion.
  • BananaPi M3
    Uses the All­win­ner A83T chip­set
    Spe­cific­ally states sup­port for MIPI DSI and MIPI CSI inter­faces, with ded­ic­ated head­ers.
    How­ever this isn’t avail­able yet, when con­tac­ted Sino­Voip sug­ges­ted it should be out around the end of this year.
  • Rasp­berry Pi
    The Rasp­berry Pi uses a Broad­com chip­set which sup­ports and has a header for 2 lane MIPI DSI out­put.
    How­ever due to driver issues this out­put isn’t gen­er­ally useable.
    There are com­plex pro­jects made with cus­tom hard­ware to con­vert the HDMI out­put to MIPI DSI.
    The Rasp­berry found­a­tion pro­duced a screen which uses the MIPI DSI out­put with ker­nel sup­port. Appar­ently they man­aged to do it in such a way that gen­eric boards aren’t sup­por­ted, just theirs.
  • Lemon Pi
    Uses an Actions S500 chip­set
    Spe­cific­a­tion states sup­port for MIPI DSI but doesn’t spe­cify how many lanes and the S500 doc­u­ment­a­tion doesn’t men­tion DSI.
    Not yet avail­able, indic­a­tions that things are hap­pen­ing so may ship this year.
    Includes (optional) built in boot­able per­man­ent storage.
  • Other boards
    There are other sys­tems out there which aren’t suit­able for vari­ous reas­ons.
    For example the H4 Hum­ming­bird uses the All­win­ner A31 with MIPI DSI out­put but at $70 isn’t competitive.
  • Mak­ing choices

    I have ordered the offi­cial Sino­Voip 7″ LCD touch­screen. This is a non-IPS 7″ dis­play con­nec­ted to the LCD con­nector via a ded­ic­ated adaptor board. It also includes a touch­screen, no details so am assume it is a capa­cit­ive panel. The main reason for get­ting this screen is that as it is dis­trib­uted by Sino­Voip it should be well sup­por­ted, the price is rather high but I haven’t inquired about pro­duc­tion quantities.

    I am also nego­ti­at­ing an order of the Top­foison 6″ IPS screen with HDMI adaptor. The adaptor seems to add about $5 – 10 USD per unit and I expect a HDMI cable will be a few dol­lars, so the wir­ing ends up being a sub­stan­tial per­cent­age of the screen costs. Cur­rently using MIPI DSI dir­ectly isn’t an option but I will def­in­itely ree­valu­ate down the track once the next gen­er­a­tion of boards comes out.