What is the current limit for each usb host port for the Pocket P.C?
As i want to be able to connect a laptop size USB HDD with 5v 0.9A 4.5W rated power consumption. So i can use the pocket computer as a ultimate music player with a 4TB USB HDD strapped/stuck to the back :). So i can have have all my music with me, in lossless and a usb DAC also stuck on the back for audiophile low noisefloor headphone amp/lineout.
Thank you
Looking at the pcb schematic.
It looks like for the usb port power, TPS2069 is used. Which has a 1.5A Continuous Current limit. As port 1 and port 2 have there own tps2069 each. Would it be correct to say usb port 1 and 2 have a 1.5A constant limit?
Thank you
Sounds like a cool application of Pocket P.C.
To answer your question:
The top left port has it’s own dedicated TPS2069 which is limited to 1.5A.
The bottom left, USB Host, and bottom right port, which is an OTG port, are both powered by a a single TPS2069 which is also limited to 1.5A.
The device has a SY7088 5V boost regulator which is capable of providing up to 2.7A of current.
It would be safe to use the top left port to power your USB HDD and the bottom left port for your USB DAC.
Thanks muchly for the reply 
That sounds like an interesting project. I once had a similar idea, but I tried using a DAC with my phone and I quickly realized it’s a no-go, in order for it to be usable I’d need to put everything in one case, with no cables hanging out of it.
But everyone has different needs, so that’s just something to think about and it’s up to you to decide whether you’d be happy with your setup.
Leaving usability behind, let’s talk batteries. The biggest problem with this kind of setups is that all the components combined will be a huge battery drain. The hard drive is by far the biggest problem, so although expensive, it could be fixed by using a low-power SSD instead. Or just a bunch of SD cards in a JBOD configuration. Only one SD card would be powered up most of the time.
Next is the SBC itself. From my experience, those are more power hungry than a typical smartphone, so you already need a decent size battery even with no external hardware attached. You could save some power by using a monochrome OLED panel.
As for the DAC, it totally depends - just stick to the ones designed for portable usage and you should be fine. For example, my FiiO E17k is quite small and I think it lasts at least 5 hours of normal listening on its own internal battery.
All things considered, you’d need to make lots of compromises to make it fit in a pocket and last longer than 15 minutes on battery 
Are you willing to build yourself a clean Linux distribution with minimal power consumption and just enough UI packages to support your OLED screen? Don’t forget you’ll also need to implement the audio player to work with it and probably some custom controls.
I think a relatively powerful MCU, such as ESP32 (or maybe something more powerful) could do a better job, as you don’t actually need a full Linux-compatible computer to decode FLAC files and push them into a USB DAC. The key advantage here is that this kind of devices can last days on a battery from an old dumb phone.
I just realized you’re talking about the model with screen and keyboard. Nevermind the part about display and controls, I realize it’s way easier to set up the software this way, although more power hungry. I guess it could last a couple hours with a very low power DAC (or one with its own battery). But I still wouldn’t use it with an external HDD, especially if it’s a 3.5" one. Are there any 4TB 2.5" HDDs? I don’t think so…
thats ok. there are 2.5 tb hdd. i have one already. was around £80 in 2020
yep i assume it will need a usb power bank for longer run time. I dont intend it to be pocket side. i know it won’t be! i made a food tub box computer before using a SBC. a fair about of work but one day sd card crashed i guess and i gave up getting to work again. never bought lexer sd cards ever again! thankfully there are now app A1 rated sd cards :smiley.
dangling cables are a pain. was going to see what neat, short right angle usb-c to usb 3 micro cables there are for the hdd.
Heh i infact already have fiio e17k. 2 in fact… i would use one for this or my hifimediy dac/headphone amp.
i was going to use it with a sound system, so compared to the tons of kit. its small and lite in comparison. would fit inside the case with the amp electrics on or straped to a diy boombox. maybe the dj software Mixxx could run on it. then with a dj controllor makes for mini low power dj setup :). Gotta lean djing then XD but thankfully i already know of some djs :).
currently i am use Fiio M3K for a DAP with rockbox open source firmware on it 
. i love it. been using it with my diy boomboxes. also what i can use for personal use. its so tiny and compact. shame its glued together. replacing the batt one day will be a pain!
also currently am converting my music collection from flacs to opus for a portable device copy. to see how small it is lossy. i guess it still will be huge. ill be lucky if it fits on 1tb. there are thankfully 1tb micro sd cards now but they do cost £180. Was so tempting but then for that sort of money i could get a pocket pc…
some vids of what i have been upto http://yt.aross.me
and some pics of some projects https://joindiaspora.com/tags/mytechproject