Re: Desperately trying (this is the correct one) ... (Happy) end...


Wiggins, Rick
 

Hi Ray,
I just want to second all your points. USB is very convenient, but
Ethernet is much more robust. I also find that serial is very robust.
Rick

--- In ap-gto@..., "Ray Gralak" <rgr@...> wrote:

Hi John,

There are many examples of USB unreliability if you search the net
(as with
almost any other hardware interface). I've personally seen USB
errors happen
hundreds of times in my day job. And they *absolutely* do happen
to USB
storage systems. I think for storage systems to be reliable the
firmware/software app needs to confirm the writes and repeat if
necessary.

In any case I think USB is a bad choice for telescopes/cameras in
general.
Ethernet is far more robust and works on every system available
without
having to create a driver. Also, USB plugs can come out too
easily. Ethernet
connectors have a more reliable plug, and even if it does get
unplugged
won't bring your mount link down if you use a connectionless
network
protocol (i.e., UDP).

-Ray

-----Original Message-----
From: ap-gto@... [mailto:ap-gto@...]
On Behalf Of John Winfield
Sent: Thursday, December 13, 2007 12:48 PM
To: ap-gto@...
Subject: [ap-gto] Re: Desperately trying (this is the correct
one) ... (Happy) end...

Hmm, I'm not sure I'd agree - my day job is developing USB based
storage systems and if it's good enough for reliably
transferring tens
of megabytes of data per second, it can probably cope with a few
ASCII
characters.

Presumably he's aware of the (lack of) robust error checking on
an
RS232 serial line?
The single parity bit on RS232 isn't very reliable - the USB
datagrams
are CRC32 protected.
I think the AP mount uses 8-N-1, so there's not even parity
checking
being performed on the RS232 comms currently.

John

--- In ap-gto@...
<mailto:ap-gto%40yahoogroups.com> , chris1011@ wrote:

In a message dated 12/12/2007 10:01:20 PM Central Standard
Time,
rdcrisp@ writes:


another suggestion is to abandon serial ports entirely,
as has the pc
industry across the board largely, and just adopt USB or
USB2.0 etc.
USB is not robust, according to our software engineer. It
can result in
dropped bits that can cause problems.

Rolando


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