[Coco] Re: atari USB device

[jdaggett at gate.net]

Dave 

Where I was definitely wrong on the Isochronous mode is that the limit is 1023 bytes 
per pipe, not packet. 

My understanding is at 1.5 Mbps, one bit time is 667 nS. So in 1 mS one can 
transmit 1500 bits or ~187 bytes theoretically. Add in the overhead for polling and 
the actual data bytes transmitted is markably reduced. It seems realistic that 8 bytes 
to 64 bytes of actual data would be a limiting amount in what can be sent in the 1 
mS time slot. 

Considering that there initially be few devices on the bus, peripherals like the 
keyboard or mouse can be allocated more bandwidth. 

james


On 22 Nov 2004 at 8:51, Dave Gacke wrote:

From:           	"Dave Gacke" <dgacke at ektarion.com>
To:             	"'CoCoList for Color Computer Enthusiasts'" 
<coco at maltedmedia.com>
Subject:        	RE: [Coco] Re: atari USB device
Date sent:      	Mon, 22 Nov 2004 08:51:29 -0600
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> 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>
>  <mailto:coco-
> request at maltedmedia.com?subject=subscribe>
> 
> > 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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