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.