http://rhombus-tech.net/community_ideas/laptop_15in/news/
it's by no means perfect, but i have at least data on-screen. i
suspect EM interference is causing the corruption, so another revision
of PCB1 will need the LVDS IC layout to be reworked. this is however
huge progress. the only 2 parts of PCB1 that need to be checked and
debugged are the MicroSD card slot and the 1W speaker/headphone
amplifier circuits. the CM108AH USB Audio IC has already been
confirmed as operational on the USB …
[View More]bus, as has the GL850G and the 3
USB ports.
l.
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i've got an enquiry out with Linear, however it looks like there's a
serious design flaw with the LTC4155 - not one that's safety-related
but one that makes it functionally completely useless.
the clue is in looking at page 15 of the datasheet - a diagram which
shows the internal operation. in the bottom left corner is a
power-selection arrangement, where there are two AND gates. note that
they're not symmetrically arranged. the difference between the two is
that WALLSNS output is connected …
[View More]to the *input* (inverted) of the
USBGT enabler AND gate.
what that means is that it is ABSOLUTELY CAST-IRON GUARANTEED - i.e.
hard-wired in an inviolate way - that if the 5VDC input is plugged
into a wall charger, USB OTG Host Power is ABSOLUTELY 100% WITHOUT
FAIL ABSOLUTE guaranteed to be terminated without warning.
which:
(a) violates the USB-OTG Power Specification
(b) is in direct contravention of the statement on page 1 of the
LTC4155 datasheet which *clearly* states that the LTC4155 is compliant
with USB-OTG Host Power Mode
(c) is in clear violation of various laws like "Trade Descriptions
Act" of the UK due to the qualifier statement in paragraph 2 which
reads "....without needing additional components".
all of which is a frickin nuisance, as i now have to go find
alternative dual-supply OTG-compliant [boost-mode] battery charger
ICs. i've found two already - bq24192i ($7 in low volume and it would
require a 2A 5V step-up converter IC as well....], or the MAX77818
which is a 0.4mm pitch BGA - perfect because it even has battery
status monitoring built-in, but the 0.4mm pitch BGA _wow_ that's gonna
be tough for small china pcb assembly factories to deal with when
they're used to QFNs and QFPs.
argh!
i'll let people know how this goes: i'm expecting to hear from Linear,
they *might* confirm that the I2C "REQUEST_OTG" mode does in fact
honour the USB OTG Host Power mode properly. if they do, then all is
well - otherwise i will need to do a redesign of PCB3.
l.
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> [*] https://developer.qualcomm.com/hardware/dragonboard-410c
>
> ("Free graphics possible" according to the Debian Wiki's ARM 64 port page...
>
> https://wiki.debian.org/Arm64Port
Adreno GPU. niiiice. minimalist hardware datasheet (with pinouts
but not mechanical layout) on arrow electronics, as well as a five
THOUSAND page datasheet on the hardware registers.
this might actually qualify as an FSF-Endorseable processor, and,
with a bit of work, might actually be a great …
[View More]candidate for an EOMA68
CPU Card. it will need a MIPI-to-RGB/TTL converter IC on-board.
there's I2C, UART, SPI, 2 SDCs (one is eMMC, the other is SD/MMC),
only one USB port (bleeeergh!), which means that a USB Hub IC is
needed..
so we're looking at... whatever the SoC cost is (knowing qualcomm
they'll want around the $12 mark for it), plus USB Hub IC and
components ($1.50), plus a MIPI-to-RGB/TTL converter IC (could be as
high as $2.50), so we'd be looking at what.... $15....
... and the allwinner A64 we know is only $5. with 2 USB interfaces,
RGB/TTL output....
whyy, god, whyyyyy... :)
l.
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.... i have the LTC 4155 15W power IC as well as the STC3115 battery
monitor ICs recognised on the I2C bus with 5V power applied, yippeee.
embarrassingly, i had the 5V DC socket wired reverse-polarity. this
is, uhh, an officially-sanctioned test of the reverse-voltage
protection on the power board design. no, really :)
on a 2nd (minimally-populated) board i have the 5V regulated output
up, but not on the fully-populated board. what i'll do is fill in all
the components from the minimally-…
[View More]populated board, testing it as i go
along.
i'm looking forward to _not_ setting fire to the apartment when i plug
in the e-bike lithium battery. unlike many of these "laptop"
batteries it has no current protection circuit built-in, and it's
perfectly capable of delivering 20 amps maximum current :)
l.
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ok, been quite busy, 3 to 4 different things going on.
first one: i've been working on getting the eoma68-a20 board up and
running (booting) out of NAND flash, that's been quite hair-raising.
using a sunxi 3.15-10-rc5 kernel i was able to use the standard
mtd-tools package to erase and write to the hynix TSOP48 NAND chip,
placing an SPL-enabled recent version of u-boot onto it. this all
worked fine... except it turns out that MLC NAND can self-destruct
just by reading! all i can say is, no …
[View More]wonder allwinner's bootloader
process is so damn complex! it's like a 4-stage boot: boot0 (minimum
bring-up), boot1 (capable of reading NAND as well as SD/MMC FAT
partitions), then u-boot (modified to read allwinner's strange
partition format) and finally linux kernel.
second, the jz4775 CPU Card is finally underway:
http://rhombus-tech.net/ingenic/jz4775/news/
this is the first FSF-Endorseable CPU Card, using the 1.2ghz low-power
Ingenic MIPS. it seems strange to put a $3 processor alongside $2.50
of NAND Flash and then put in almost $12 of DDR3 RAM ICs (2 GB RAM)
but the threshold where SoCs were no longer the most expensive part of
a BOM was passed a loong time ago.
third, the laptop main board, i've got everything working except the
LCD. i've blown up 2 LCDs already, it was necessary to buy 2 more.
first mistake was that it was hard to read the datasheet so the
connector was reversed: that resulted in -20V being shoved up the
backside of the +3.3v sensitive ICs on the LCD, end result when i was
finally able to make up a reversed-cable, the "magic smoke" left that
LCD. also i hadn't noticed that i'd shorted the 5V rail to the 3.3v
rail, which didn't help, and may have damaged some of the GPIOs on one
of the EOMA68-A20 boards i have here. still quite a bit to
investigate there.
fourth, i've managed to smoke about 3-4 Power ICs already - various
MOSFETs, two 3 Amp RT8288 PMICs from microdesktop boards i'm using for
test purposes - all to get the laptop power / charger board up and
running. annoying! but finally a couple of hours ago, by making up a
2nd board with minimal components, i managed to get the LTC4155 up and
recognised on the I2C bus, as well as check that it was outputting
stable 5V from USB-style input. the next phase is to populate the
over-voltage and reverse-voltage protection components.
it's getting there... it's just slower than i would like.
l.
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yaaaaa, i have battery-operation, i am currently running an eoma68-a20
off of a 10Ah e-bike battery, and both the LTC4155 charger/dual-supply
IC and the ST3115 battery guage IC are up and recogniseable on the I2C
bus.
i have yet to compile up the linux kernel modules for both these
devices, but they are both available... somewhere :)
only slight issue to track down: power drops to 4V when the 5V DC is
plugged in, i still have to investigate that, but it may be related to
the setting of 3A …
[View More]input and i only have a 2A 5V charger. i can change
the settings, and i can also "ping" the LTC4155 over the I2C bus...
maybe :)
but.... progress, yay!
l.
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