[LAU] Portable/Touch devices Linux friendly

david gnome at hawaii.rr.com
Sat Dec 1 23:34:48 UTC 2012

On 12/01/2012 06:20 AM, Len Ovens wrote:

> On Sat, December 1, 2012 1:04 am, david wrote:
>> On 11/30/2012 06:47 AM, Paul DeShaw wrote:
>>> Have you seen the ZaTaB  (http://zareason.com/shop/zatab.html )?  Open
>>> bootloader, made for hacking.
>> At the moment, I'm not interested in hacking. I'm willing to root
>> another vendors product if I need to. ;-)
> How easy is it to get things with "micro" USB plugs on them? Taking
> adapters everywhere I go sounds like something I don't want to do. Only
> two USB ports? Assuming an external Audio IF and a keyboard (or MIDI
> IF)... nothing left.

Adapters would be the way to go. It has wifi. Maybe use it as a control 
surface, with MIDI IF connected to it, and connect to an external PC for 
sound generation? But that's a lot more than just an adapter or two.

Most of the keyboards for typing on tablet computers use Bluetooth, so 
the shortage of USB ports wouldn't be a problem.

>>> I haven't seen one in person.
>> I've looked at it, haven't seen one in person. I'm disappointed with the
>> low resolution and the weak processor compared to the Kindle Fire HD or
>> the Nook HD+ 9 tablets. Both of those tablets can be rooted and have
> For Audio, my question is are the USB ports on their own IRQ? On any of
> these? In fact we should be writing to the manufactures and asking which
> model USB ports on their own irq. (same with PCI(e) slots) Maybe if they
> thought it was something people were not buying their stuff because of...
> that would be something they look into. The new irq controllers seem to
> have way more irqs than are used.

Haven't a clue.

> As an example, I have an Acer aspire netbook with 3 USB ports. The left
> side port is USB2 and shares its IRQ (16 I think) with lots of things. The
> other two plugs are both USB3, but USB3 has it's own IRQ. If I plug my
> Audio IF into USB2, forget low latency work... Jack still get xruns once
> in a while at -p1024. However, if I plug it into USB3 (on its own) I can
> run -p64 without xruns (till I over use the cpu). This is a USB1.1 device,
> so it is not asking for much bandwidth... (ART USB Dual Tube Preamp)
> However, USB 2.0 might handle this better.

My desktop PC has USB3. When I connect my USB2 card reader to it, 
throughput goes way down compared to when connected to my laptop's USB2. 
Don't know why, it just does.

> In general, it seems that the computer world (hardware and software) has
> decided to maximize throughput at the expense of latency. I was looking at
> the spec for PCIe transfer (version 1 - 4) and it seems optimized for
> throughput as the version increases. The early versions sent fewer/smaller
> packets through for each header and so the header itself was smaller. The
> later versions seem to have larger packet sizes, and send more packets
> through per header (great for throughput), but the header is now bigger.
> In low latency audio work, the idea is to get a small packet of data
> rather often but that small packet would be burdened with padding to make
> up minimum packet size plus a large header packet to go with it. I am not
> sure the the minimum number of packets per header may need to be used as
> well (all zeroed out if we don't need them) I have not looked at the USB
> specs for transfer to see if there is a similar trend or not.

Commercial OS manufacturers are pushing computers as devices for 
consuming, not producing. Latency doesn't matter when watching a movie, 
just steady sustained throughput. Tablet computers are viewed as 
consumption devices even more than non-tablets ...

> In the hardware world, there seems to be the idea that sharing irqs is
> fine if the buffer size(read latency) for peripherals kept large.

I don't know why they share them, either.

I think the manufacturers' main focus is always on, "How can we make 
this cheaper?" ;-)

gnome at hawaii.rr.com
authenticity, honesty, community

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