linuxaudio.org

On 12/01/2012 06:20 AM, Len Ovens wrote:
> On Sat, December 1, 2012 1:04 am, david wrote:

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>> 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.

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>>

>> 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

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> 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

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> 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

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> 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?" ;-)
--

David

gnome@hawaii.rr.com

authenticity, honesty, community

http://clanjones.org/david/

http://dancing-treefrog.deviantart.com/

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