[Coco] Re: atari USB device

[Dave Gacke]

Hi James,

Unfortunately your math is a little off.

The part that everyone seems to miss about USB is the poll time. Since it is
a polled device bus, at low speed, your polls come at 10ms intervals, and
full speed they are at 1ms, and I forget what they are at high speed.

Anyway, you are severely limited by the rate at which you are polled. Per
poll you can pass 1 packet, so its easy to figure out the throughput from
that.


Dave

-----Original Message-----
From: coco-bounces at maltedmedia.com [mailto:coco-bounces at maltedmedia.com] On
Behalf Of jdaggett at gate.net
Sent: Sunday, November 21, 2004 7:34 PM
To: msmcdoug at optushome.com.au; CoCoList for Color Computer Enthusiasts
Subject: Re: [Coco] Re: atari USB device

Mark

In handshake mode at high speed the data payload is either 8, 16, 
32, or 64 bytes. In Low speed mode the max data payload is 8 
bytes. Well capable for the Coco.

Isochronous mode, without hondshakes,  the data payload is limited 
to 1023 bytes.  

This is per the copy of the USB 1.1 Specs that I have. 

I personally think that Isochronous mode should never need to be 
used. 

What Torsten was thinking of was that a sector size for a Coco disk 
is 256 bytes. The SL811HS has the upper sixteen bytes of the 
buffer reserved for registers. This would leave the largest packet 
data size of 240 bytes. That ends up being 16 bytes shy of a disk 
sector. 

The only way to read a complete sector would be to break the 
sector up into 4 64 byte packets. Each packet would take 42.7 
microseconds to transfer and about 512 machine cycles to do a 
load and store for the Coco. At  high speed that is about 286.2 
micro seconds. Essential about 1.5 milliseconds to transfer data 
from a disk into the Coco. 

Not sure if we gain that much speed advantage. But maybe some. 
The Disk drive itself is really the slow element of the whole process. 

james


On 22 Nov 2004 at 9:42, Mark McDougall wrote:

Date sent:      	Mon, 22 Nov 2004 09:42:27 +1100
From:           	Mark McDougall 
<msmcdoug at optushome.com.au>
Organization:   	Technetium Development Pty Ltd
To:             	CoCoList for Color Computer Enthusiasts 
<coco at maltedmedia.com>
Subject:        	Re: [Coco] Re: atari USB device
Send reply to:  	msmcdoug at optushome.com.au,
	CoCoList for Color Computer Enthusiasts 
<coco at maltedmedia.com>
	<mailto:coco-
request at maltedmedia.com?subject=unsubscribe>
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> USB data packets (at least v1.x) are only 64 bytes in length. So I'm
> not sure what the 240 bytes refers to in your post. With the USB
> protocol handling the handshaking the CoCo is left to emptying the
> 64-byte packets as fast (or as slow) as it likes. I really don't see
> an issue here.



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