Hi Luc,
On Mon, 13 Sep 1999, Luc Hermans wrote:
> In my embedded linux application I've written a modbus interface (RS485)
>
> on /dev/ttyS1 (cfmakeraw) the RTS is used to enable/disable the RS485
> driver.
>
> I use the ioctl(fd[c], TIOCMSET, &status) fucntion.to change RTS'
>
> Before sending I enable RTS, send all data, (the RS485 echo's all)
> wait until all data is received, and then disable RTS.
>
> The problem is that the RTS is sometimes dropped to slow, up to 5ms,
> witch is to long (because I get an answer from the polled device withing
> 3ms)
> but sometimes also fas, lesser then 500us.
>
> What is the cause of this ?
> I work with an i386 40MHz cpu at 9600 baud
This is because of task-switching within the kernel. You may circumvent
this by putting your protocol inside a device driver, as I have done with
my "driver for KeenView". This is similar to yours, a RS-485 network with
multipoint microterminals. Please look at my home page for the driver.
If you need some assistance, I will be happy to give it.
best regards,
Rildo
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