On Thu, Dec 15, 2011 at 09:30:04PM +0100, Torbjörn Lofterud wrote:
>
> Hello.
>
> I think that i might have found a small bug.
>
> Im trying to communicate with the ECU in my Volvo Car and those
> people at Volvo figured it would be a smart thing to communicate
> at 10400 baud.
>
> As a Linux geek I want to hack my car from Linux, so i set out to convince
> the ftdi_sio-driver to run at 10400 baud. As Im sure you are aware of
> custom baud-rates are a bit under-documented.
>
> Using the custom divisor the value 2308 or 2307 gives me values that is
> reasonably close to 10400, but not 10400. In order to get the quotient of
> the division to be exactly 10400 i need to change the baud_base. But im
> unable to actually change the baud_base value.
>
> Looking at the source the function set_serial_info() does sanity checking
> on the newly provided value, and im able to provoce the -EINVAL if i give
> it a value below 9600. But the code never actually updates the priv-struct
> with the new value.
>
> if ((new_serial.baud_base != priv->baud_base) &&
> (new_serial.baud_base < 9600)) {
> mutex_unlock(&priv->cfg_lock);
> return -EINVAL;
> }
>
>
> So, currenly im unable to get 10400 baud :(
>
> Am I doing it wrong, or is it a bug in the driver?
It is a bug _and_ you're doing it wrong. ;)
It's not possible to change the device specific baud_base so it's only
the above construct which is incorrect.
This seems to be due to a misunderstanding some years back (see
https://lkml.org/lkml/2005/1/20/84).
> Is there a better way to set the device to 10400 baud than to use the
> custom divisor?
AFAIK you're stuck with using a custom divisor.
Thanks,
Johan
> --- How to repeat:
>
> # setserial /dev/ttyUSB0 baud_base 9600
> # setserial /dev/ttyUSB0 -a
> /dev/ttyUSB0, Line 0, UART: unknown, Port: 0x0000, IRQ: 0
> Baud_base: 24000000, close_delay: 0, divisor: 2306
> closing_wait: infinite
> Flags: spd_cust low_latency
>
>
> Expected value: 9600
> Recieved value: 24000000
>
> Kind regards
> Torbjorn Lofterud
>
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