[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [bluetooth-dev] Bluetooth module/serial port latency



On Fri, 15 Jun 2001 shemang@xxxxxxx.com wrote:
Hemang,
 The driver has not latency itself. I tested this by programming the
serial port directly using outb's and inb's and hooking 2 PCs
with a wire through the serial port. There was no latency in writing
to the port with the serial.c driver by Teo Ts'O (supplied with Linux).
It ran almost as quick (95%+ speed) as direct outb's and inb's.
 The problem is I don't know what's the minimum latency I can get
with the bluetooth serial port interface. Are you sure it's the driver's
latency that's delaying me? What's the fastest time you've ever got
when sending an ACL data package over (time between when you write to
the serial port till the other host receives from its serial port)?
 I'm not really using or writing an HCI driver. I'm just writing
commands and data to the port and then wait(poll / read) for events
or data in reply.
 Again, thanks for your help and I'd appreciate if anybody could
enlighten me on this latency stuff cause it looks that bluetooth
is streaming fast but it doesn't get a fast start...

 v v

> Vladimeros,
>  I presume your reading or writing to the serial port and the time in which
> it sends depends on a lot of factors on Linux..
> for example the number of modules in the kernel. the number of processes
> running, etc. There would be no way to say that you could send out the
> whole packet in 15ms. If you are using sk_buff structures and the memory
> management associated with the sk_buff structure you should be able to do
> it without either packet loss or packet corruption most of the times..
>  If you are using the HCI driver and the UART driver interface you should
> use a UART driver which uses this kind of memory management. You could use
> the tp4bduart driver from www.alphaworks.ibm.com for this..though.
>
> Hemang C S
> Networking Software Group, IBM Software Labs, India,
> 7B1,Golden Enclave, Airport Road,
> Bangalore - 560017
> email ID:shemang@xxxxxxx.com
> Ph no. 91-80-5267117 Ext. 3715
>
> Think!!!!                                                   Think!!!
> Think!!
>
>
>
> Vladimeros Vladimerou <vladimer@xxxxxxx.edu> on 15/06/2001 00:45:26
>
> Please respond to Vladimeros Vladimerou <vladimer@xxxxxxx.edu>
>
> To:   bluetooth-dev@xxxxxxx.com
> cc:    (bcc: Hemang C Subramanian/India/IBM)
> Subject:  [bluetooth-dev] Bluetooth module/serial port latency
>
>
>
>
> Hi everyone!
>
> I'm using an ericsson BT Application Kit on a linux machine and I'm
> trying to write my own HCI driver using the serial port.
> I'm using the read() command to read from the /dev/ttyS0 file.
> I need to get 32-byte packets going back-and-forth two machines
> through the bluetooth modules. I need a packet to reach the destination
> host in less than 15ms. Is that possible?
> Right now, if I try to read from the ttyS0 file for data before the
> other module starts sending it, I get errors. Some zeros get inserted
> in the beginning and I lose some bytes in the end.
> When I wait though for 1 second after the data was sent from the
> remote module and THEN read the port, I get zero errors and no
> latency.
> Does anyone know what's going on here?
>
> v v
>
>
> -
> To unsubscribe from this list: send the line "unsubscribe bluetooth-dev" in
> the body of a message to majordomo@xxxxxxx.com
>
>
>
> -
> To unsubscribe from this list: send the line "unsubscribe bluetooth-dev" in
> the body of a message to majordomo@xxxxxxx.com
>

-
To unsubscribe from this list: send the line "unsubscribe bluetooth-dev" in
the body of a message to majordomo@xxxxxxx.com