[ltp] Some experiences with serial ports, internal modem and

[linux-thinkpad@www.bm-soft.com]

On 26-Feb-01 Thomas Hood wrote:
> --- Till.Straumann@TU-Berlin.de wrote:=20
>> Some remarks on IRQ sharing among serial devices and IR port
>>=20
>>  - serial irq sharing must be enabled in the kernel
>
...
>=20
> Qualification.  I am running Linux 2.4.2.  I did *not* select
> CONFIG_SERIAL_SHARE_IRQ=3Dy. =20

Well, I'm still running 2.2

>
>>  - I also made the experience that after unloading the FIR
>>    driver, things became sometimes unstable. Especially,=20
>>    the using the "irtty" after having used the FIR driver
>>    does _not_ work. BTW: I use dongle_id=3D0x9 for the FIR...
>=20
> This is a bug, I presume.  Any idea of where the bug is?

Unfortunately not... It's also quite old (already present
~1 year ago)

>=20
>>  - IRQ sharing with the MWAVE modem does not work
>=20
> But it might work if the serial driver were a module
> which wasn't loaded at the same time as mwavedd.o ?

Of course - to make absolutely sure that there's no
conflict, you may also selectively disable/enable irqs
using the setpnp tool. "Interrupt sharing" means several
devices using the same line _concurrently_.

> Since the motivation for sharing interrupts is not
> having enough interrupts to go 'round, I should point
> out the following.
>=20
> - Serial and parallel port drivers only "grab" the interrupts
>   they use while they are loaded and their corresponding 
>   device nodes are open.

yep. It's possible for drivers that dont implement irq sharing
to use the same line if they are not really using it concurrently.

> - The parallel port will work without using an interrupt.
>   The parport_pc driver is capable of "polled" operation.

The serial driver also.

> - You only need to assign an IRQ to "MIDI" if you are=20
>   using the MPU-401 UART to communicate with an *external*
>   MIDI device.  The 98% of use who don't have external
>   MIDI devices need only one interrupt for the sound card.

AFAIK, there is no access to the MIDI UART unless you have
a docking station...

--Till.

BTW: when you this message has been routed by LINUX
running on an Apple Airport Wireless LAN router :-)

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