Re: [Bluez-users] Once again: Socket CF card and Kernel 2.6

[Marcel Holtmann <marcel@holtmann.org>]

Hi Mathias,

> > > I just got it working by doing a little change in the serial driver 
> > > (8250.c). I tested it with 2.6.11 but I think it could work for any 2.6 
> > > kernel.
> > 
> > please provide a patch for your change.
> 
> So - after some cleaning - here it is. A short description:
> 
> The BlueZ driver requests a baud rate
> of 230400 which is uartclk/8 (serial_cs sets uartclk=1843200). However
> serial8250_set_termios() refuses to program a baud rate larger than
> uartclk/16 which should be ok for most UARTs. I looked into the 2.4
> driver and found some code that changes the internal prescaler to values
> between 1:16 and 1:4 to support baud rates up to uartclk/4 respectively
> (this is done for 16C950 UARTs only). The datasheet of oxford's oxcf950
> chip confirms this feature.
> 
> Apply the patch to the file drivers/serial/8250.c
> 
> Please let me know if there are problems or if it does work.

I only have the old Socket cards (dtl1_cs driver) at hand and so I can't
test it, but my Xircom card is still not working.

> > > One thing I discovered while debugging this: the hci_uart driver 
> > > seems to initialize the actual UART with only 230400 baud. Is this 
> > > really the case or are those UARTs clocked at nonstandard (higher) 
> > > frequencies so that this setting does result in a higher real baud rate?
> > 
> > The hci_uart is only a line discipline. Every initialization and baud
> > rate settings are done with hciattach.
> 
> ok so it's hciattach that sets the baudrate - but that wasn't the point
> (or I misunderstood your answer?): I wonder if the bluetooth module is
> really accessed at only 230400 baud (that's the rate which is given to
> the 8250 driver) which seems a little bit slow thinking of bluetooths
> >700kbaud maximum rate...

For the Socket card the baud rate is 230400 and yes, this is to slow for
the full bandwith of a piconet. However I never did any bandwith test
with this card, but actually there are cards out there where the UART
limits the total possible bandwidth.

Regards

Marcel




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