On 12/14/16, Benson Mitchell benson.mitchell+arm-netbook@gmail.com wrote:
On Tue, Dec 13, 2016 at 9:51 AM, dumblob dumblob@gmail.com wrote:
Can we provide both interfaces (RGB/TTL + MIPI DSI) on the same pins while having a HW way to choose from these?
Yes we can! EOMA already counts on several types of PC Cards (originally called PCMCIA). At minimum two - thinner (Type I - 3.3 mm) and thicker (Type II - 5 mm). Let's declare the thicker cards to be high-end and offer only MIPI DSI while thinner cards low-end with just RGB/TTL. Problem solved!
To be specific, EOMA68 includes Type I, Type II and Type III already. There are differences in permitted power, and RGB resolution. These differences run in opposite directions, in order to make sure that any combination that fits will work.
WRT resolution, Type I is the high-end, with card-minimum/housing-maximum 1920x1080, because a Type I housing will accept _only_ Type I cards. Thus anything with a 1920x1080 screen has a Type I slot, and any card that physically fits will drive that display.
nooo, 5.0mm is the 1366x768 because the 5.0mm needs to be prevented and prohibited from being physically inserted into incompatible 3.3mm (1920x1080) slots.
(AIUI, a Type II housing can have a 1920x1080 display, as long as that display will accept and upscale a 1366x768 signal.
NO. absolutely not. that is a completely unacceptable technical burden on the manufacturers of the housings, forcing them to have additional circuitry which may or may not be used.... and may or may not be actually available on the open market.... and may actually end up being far more costly than the processor utilised in the Card.
any kind of resolution scaling at these framerates and buffer sizes it actually needs a full processor - with several hundred megabytes of DDR2 / DDR3 RAM - to perform the conversion.
so no - absolutely not. you connect the LCD to the EOMA68 bus on the Housing, the LCD's resolution is fixed as decided by the manufacturer of the Housing, and that's the end of it.
Then either a Type I card or a Type II card exceeding the minimum specs can output full 1920x1080, but it will work with even the minimum Type II card's 1366x768.)
The point is, any card _must_ work in any housing it physically fits in. So if you want Type I to support MIPI, that's great -- but that Type I still fits in a Type II, so it must also be able to output RGB/TTL on the same pins,
... correct.... but worse than that it must be on the *exact* dual-function pins as arbitrarily specified in the propsed [completely not-thought-through] standard.
and there must be a mechanism to autonegotiate this depending on the housing.
correct.
I don't think adding autonegotiation here is particularly hard (basically just defining a flag in the I2C EEPROM),
correct.
but the need to support both interfaces negates some of the benefits of MIPI,
not really relevant
and adds complexity to all cards supporting MIPI,
"insane, hard to implement and with ICs that probably don't actually exist" complexity
and I'm not sure that complexity (multiplexer, and in some cases, MIPI->RGB conversion IC) can actually fit on a crowded EOMA68 card.
correct.
The "high-end" specification shall then also be extended allowing higher thermal dissipation (5W is too low - maybe 15W would be OK as it's still easy to cool passively) etc. to accommodate "high-end" (actually mainstream, but in this context it's high-end) requirements.
Type I and Type II are currently limited to 5W, while Type III is limited to 10W. Again, these have to be in this order, because any card must work in any housing it physically fits. So a 5W card can be powered by a 10W power supply, but not the other way around.
I think 10W is a hardware limit of the connector (4 pins at 0.5A per pin);
correct. ah, i'd forgotten about that. yeah you do not want to be overheating the pins. so, 10W limit it is.
Speaking about thermal dissipation, I'm not sure that in case of the high-end card type, this limit should be a fixed one.
Obviously, technically skilled people will overclock and overwatt specific EOMA68 cards in housings that they know can supply more power.
outside of the standard.... probably.
But the minute you change this behavior from "hackers breaking the rules" to "there are no rules", you've made it so that the whole promise of EOMA ("Just plug it in; it will work") can no longer be kept.
correct. and that's why these things have to be thought through very, very carefully, and simplly not permitted - outright banned - if there is even the slightest possibility of confusion or harm.
remember the goal is 100 million units and above per year. even the SLIGHTEST chance of confusion could result in millions of units returned, resulting in a catastrophic loss of confidence in the standard.
there is NO WAY the standard can be "sacrificed" just for the benefit of some arbitrary "nice-to-have" decision or short-term profit.
I personally would be fine with that -- in fact, I would be fine with a lot of things that are defined in the EOMA68 standard being just a matter of labeling, and leave it on the user to choose compatible parts.
as long as the compatibility is "everything, always works [even if it's a bit slower]" i don't care.
the MOMENT that becomes "it MIGHT work, but it might not" then the standard's fucked and six years (and counting) have been utterly wasted, irrevocably destroyed in an instant.
But Luke's not designing this standard for me; he's designing it for people who would get confused and buy a 25W card and a 10W-max tablet housing, and not understand why they don't work.
absolutely correct.
If you're targeting those people (which you have to, to get volume), you have to make it work for them.
absolutely correct.
this isn't a "techie standard wanna plug in yer favurit memry upgrad just undo da scruz n read duh instrucshunns on da in'ur'ne' "
just as that pc journalist said a couple months back (about gaming pcs being too hard), it's for people with big fat fingers who are afraid to drop the screwdriver and damage things.
one button.
press it.
card comes out.
put new one in.
it will work.
that simple.
and it stays that simple.
this is not negotiable.
l.