Dev16

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Mario Charest

Dev16

Post by Mario Charest » Fri Nov 21, 2003 7:18 pm

Will using Dev16 instead of Dev32 result in lower performance. I'm thing
kernel switching to 16 bit mode and back to 32 what ever that means.

- Mario

David Gibbs

Re: Dev16

Post by David Gibbs » Fri Nov 21, 2003 9:20 pm

Mario Charest <postmaster@127.0.0.1> wrote:
Will using Dev16 instead of Dev32 result in lower performance. I'm thing
kernel switching to 16 bit mode and back to 32 what ever that means.
This may depend on the x86 processor. To my knowledge, the kernel doesn't
switch to/from 16/32 bit mode, but the code is different -- different
op codes, etc. And, my understanding is that on later generation x86
processors, the execution of 16-bit instructions is slower than 32-bit
instructions.

-David
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QNX Training Services
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David Gibbs

Re: Dev16

Post by David Gibbs » Fri Nov 21, 2003 9:22 pm

Mario Charest <postmaster@127.0.0.1> wrote:
Will using Dev16 instead of Dev32 result in lower performance. I'm thing
kernel switching to 16 bit mode and back to 32 what ever that means.
BTW, why do you want to use Dev16?

I assume for one particular Dev.driver that is only available in
16-bit mode. In that case, I'd suggest using both.

In fact, you can gain performance by using multiple Dev invocations
for different sets of devices.

-David
--
QNX Training Services
http://www.qnx.com/support/training/
Please followup in this newsgroup if you have further questions.

Adam Mallory

Re: Dev16

Post by Adam Mallory » Fri Nov 21, 2003 9:29 pm

David Gibbs <dagibbs@qnx.com> wrote in message
news:bplvjm$6u5$2@nntp.qnx.com...
Mario Charest <postmaster@127.0.0.1> wrote:

Will using Dev16 instead of Dev32 result in lower performance. I'm
thing
kernel switching to 16 bit mode and back to 32 what ever that means.

This may depend on the x86 processor. To my knowledge, the kernel doesn't
switch to/from 16/32 bit mode, but the code is different -- different
op codes, etc. And, my understanding is that on later generation x86
processors, the execution of 16-bit instructions is slower than 32-bit
instructions.
It doesn't flip modes (ie. thunking), but there are different entry/exit
sequences for some 16bit stuff (mainly stack alignments and the like).

-Adam

Mario Charest

Re: Dev16

Post by Mario Charest » Sun Nov 23, 2003 5:39 pm

"David Gibbs" <dagibbs@qnx.com> wrote in message
news:bplvm6$6u5$3@nntp.qnx.com...
Mario Charest <postmaster@127.0.0.1> wrote:

Will using Dev16 instead of Dev32 result in lower performance. I'm
thing
kernel switching to 16 bit mode and back to 32 what ever that means.

BTW, why do you want to use Dev16?

Remember QWindows ;-) Think is customer is using Dev16 everywhere even on
machines that aren't using QWindows.
I assume for one particular Dev.driver that is only available in
16-bit mode. In that case, I'd suggest using both.

In fact, you can gain performance by using multiple Dev invocations
for different sets of devices.
-David
--
QNX Training Services
http://www.qnx.com/support/training/
Please followup in this newsgroup if you have further questions.

David Gibbs

Re: Dev16

Post by David Gibbs » Mon Nov 24, 2003 3:44 pm

Mario Charest <postmaster@127.0.0.1> wrote:
"David Gibbs" <dagibbs@qnx.com> wrote in message
news:bplvm6$6u5$3@nntp.qnx.com...
Mario Charest <postmaster@127.0.0.1> wrote:

Will using Dev16 instead of Dev32 result in lower performance. I'm
thing
kernel switching to 16 bit mode and back to 32 what ever that means.

BTW, why do you want to use Dev16?

Remember QWindows ;-) Think is customer is using Dev16 everywhere even on
machines that aren't using QWindows.

I assume for one particular Dev.driver that is only available in
16-bit mode. In that case, I'd suggest using both.
Yup, Dev.win is one of those Dev drivers only available in 16-bit.

I'm sure I wrote a tech-note about using a 16-bit Dev for Dev.win,
and 32-bit Dev for everything else many years back.

Yup... /windows/readme/Dev.win :)


-David
--
QNX Training Services
http://www.qnx.com/support/training/
Please followup in this newsgroup if you have further questions.

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