[Arm-netbook] laptop main board, power board and ingenic jz4775 cpu card

Luke Kenneth Casson Leighton lkcl at lkcl.net
Tue Nov 24 04:03:16 GMT 2015

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 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:

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.


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