[Arm-netbook] microdesktop v1.7 arrived, works fine... but...

[Luke Kenneth Casson Leighton]

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crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68


On Thu, Apr 6, 2017 at 1:38 PM, Joseph Honold <mozzwald at gmail.com> wrote:
> On 04/06/2017 12:12 AM, Luke Kenneth Casson Leighton wrote:
>> now, i _could_ convert to eMMC but it's too much of a major redesign:
>> it involves disrupting the RGB/TTL tracks, and may require at least
>> two more rounds of pre-production prototyping...
>>
>> ... it's too much: it's too risky... and i'm getting fed up.  so.
>> what i'm going to do instead is: cut the NAND IC entirely, then wire
>> SDC2 (which is the same pins as the NAND) to the *ON-BOARD* Micro-SD
>> card slot, instead.
>
> Not that I'm against dual SD slots, but from what I see, NAND and eMMC
> share the same pins so it should be easy enough to add the bga
> footprint and the required passives.

 should... but (a) if i get it wrong it's yet another $1500-$2000 and
yet another 8 week delay, which means that it could be $3000-$4000 and
16 weeks because it will be necessary to do *two* more revisions, one
to find out that the PCB design was wrong and one to add corrections

 and (b) yes the same wires can be used but no the boot order cannot
be changed because as it's the exact same wires there's still no room
to cross over MMC3 and MMC0 to make MMC0 the "on-board" boot and MMC3
the EOMA68 off-board microsd.

 the other alternative is to turn the A20 round by 90 degrees and to
use two DDR3x16 RAM ICs instead of four DDR3x8 RAM ICs.

 howevver...

 (a) the cost of 2x DDR3x16 RAM ICs to make up 2GB is a COMPLETELY
INSANE $20 just for the memory alone.

 (b) replacing the memory layout and adjusting the power management is
basically a total redesign of the board, i might as well chuck the
ENTIRE design away and start completely from scratch.

i estimate that would take about three revisions, thus would be
somewhere between $4,500-$6,000 and take an estimated 10-12 weeks.

 and it'll be a $40 PCB.  which there isn't enough cash for.

 basic logical reasoning says: remove the NAND IC.

l.