On Mon, Jun 02, 2003 at 06:14:31PM +0200, Peter Asemann wrote:
> Where's the difference between the nibble and the compat mode?
Nibble mode is peripheral-to-host transfer; compatibility is
> I suppose that in nibble mode you can use the "read" function which will not
> work in compat mode?
Exactly: and you can't "write" in nibble mode (that's meaningless).
> This should make not difference if, for example, some "user land" driver
> decides to read the status lines to implement nibble mode on it's
> own, I suppose?
Right. If you aren't going to both with IEEE 1284 negotiation, you
can do what you want with the status, control, and data lines.
> Regarding byte mode, I guess PPDATADIR will only work in byte mode,
Rather the other way around: byte mode only works if the data lines
can be tristated.
> So in byte mode a program that does not use read and write but reads and
> writes data and status and control register on it's own would be able to
> perform all operations possible with a tristate spp port?
'byte mode' is a logical IEEE 1284 state, achieved by negotiating to
it. It's not something the parallel port chip knows about.
> I find there's a ioctl missing which tells you if the port is in forward or
> reverse direction... but I guess if my program is interrupted by another
> program or yields the port so another program may use it, my program's
> settings regarding the direction of the port are restored... aren't they?
Yes, they should be. (If not there's a bug.)
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