- From: Ian Abbott <abbotti_at_mev.co.uk>
- Date: Fri, 18 Feb 2005 18:07:11 +0000
On 18/02/05 14:48, David Schleef wrote: > On Thu, Feb 17, 2005 at 06:35:32PM -0500, Frank Mori Hess wrote: > >>On Monday 14 February 2005 07:36 am, Ian Abbott wrote: >> >>>Hi, >>> >>>After using comedi_dio_config (INSN_CONFIG) on a DIO subdevice managed >>>by the 8255 driver, the 8255 chip sets all its output lines to 0 but the >>>copy of the output state saved by the 8255 driver in the 'state' member >>>remains unchanged. >>> >>>Would it be better if: >>> >>>(i) the 8255 driver zeroed its output state when configuring the i/o >>>directions, or >>>(ii) the 8255 driver rewrote its current output state to the chip when >>>the i/o directions have changed? >> >>I think the first option is better, since it makes more clear to the user >>that something bad has happened. If the driver rewrites the output state, >>it still won't prevent a transient glitch on the output, which could cause >>people problems. > > You're supposed to be able to write an output state to a DIO > device that is configured to input. When reconfigured for > output, the driver should change the lines from high-impedance > to the preset state. That's what my second option would do, but there would be an unavoidable glitch on any output channels that were set to 1 before the reconfiguration. Well, the driver could avoid writing the 8255 mode if it hasn't changed and so avoid the glitch in that case. -- -=( Ian Abbott _at_ MEV Ltd. E-mail: <abbotti_at_mev.co.uk> )=- -=( Tel: +44 (0)161 477 1898 FAX: +44 (0)161 718 3587 )=-
Received on 2005-02-18Z18:07:11