[Arm-netbook] moved to taiwan, started passthrough card

Luke Kenneth Casson Leighton lkcl at lkcl.net
Mon Dec 26 06:04:32 GMT 2016

ok so much of this is in the upcoming update, we made a snap decision
to go to taiwan because of the 30 limit on the china dual-entry visas.
i'm staying with a friend who has a stack of equipment including IR
oven, small pick-and-place machine, scope etc. so it's a much easier
arrangement, i'm helping him out as well.

the rk3288 board is going to first prototyping, we're getting
quotations from PCB manufacturers.  that leaves me free to move to the
next PCB design, and i picked the passthrough card... which turns out
to be much more complicated than i was expecting.  i _could_ do a
simple version (just a TFP401a) but it would have to have 2 USB ports
and a break-out arrangement for the remaining pins.... i decided
instead to wire them all to a STM32F072.

now, the idea here is to pre-load a userspace USB-based DFU bootloader
into the NAND flash, and to require firmware to be uploaded after it
reports the contents of the EOMA68 EEPROM ID.  the TFP401a's I2C will
be connected to the STM32F072, it can emulate an EEPROM and can load
EDID data which tells the TFP401a what the LCD's resolution is.

normally the LCD resolution would be fixed... but here it is not
possible to know what the LCD resolution is going to be.... also we
have no idea in advance what the various functions are of the EOMA68
pins: maybe the SD/MMC pins are used for an SD card (in which case the
STM32F072 can be programmed to be a USB mass-storage device), but
maybe they are used as GPIO, or maybe they are used for a WIFI SIP
module: we just don't know.  hence the need to be flexible and for
firmware to be uploaded on a per-boot basis.

i would _like_ to use a more powerful EC but i haven't the time to
learn a new EC... so the STM32F072 it is.


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

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