David Campbell (campbell@gear.torque.net)
Sat, 16 May 1998 08:14:31 +0000
> > does anyone know about driver or software (Linux) for the Creative Labs Web
> > Blaster II parallel port camera or any effort to write such a driver?
>
> If you have the option go for a PCI card and Composite camera pair. Parallel
> port cameras murder your performance. If you've already got the card then
> as far as I know nobody has attemped it
If the camera is operating in a "still snapshot" mode then it should be
about as bad as parallel port drive. Certain coding techniques can (and
have been) used to reduce the performance losses (the ZIP drive used to
freeze a machine so badly that "ls" would pause for several seconds
under certain circumstances).
*check web pages*
In "live video" mode the data transfer rate is approx 2.2 MB/sec
(raw) which exceeds the fundamental limit of a parallel port
(ISA bus: approx 1200 nsec per transfer => 833kB/sec, I have a little
timing program to check this one).
Using differential and data compression techniques could squeeze the
2.2MB/sec down to 833kB/sec. It may be possible to break the 833kB/sec
limit but it is dependent on several factors:
a) The ECP dma channel is unused
b) The ECP irq channel is unused
Considering how many devices (*curse soundblaster sound cards*) steal
IRQ 5, IRQ 7 and DMA 1 (most common settings for ECP ports - other values
possible) it is unlikely that these values are free.
My discussions on the phone to the Iomega driver developer for the ZIP
Plus drive indicates that comercial hardware suppliers are loathed to
include DMA support into their drivers (Iomega do not even attempt to use
DMA). For those who are not hardware hackers - DMA can transfer data from
IO ports to memory faster than the CPU, a guess is twice as fast.
Enough technical explanations, I need to get back to adding parport
support for the ZIP Plus driver.
David Campbell
=======================================================
campbell@torque.net
"All parallel ports are equal - Some are more equal than others"
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This archive was generated by hypermail 2.0b3 on Wed 30 Dec 1998 - 10:17:44 EST