baudrate detection

baudrate detection

[John Whitmore]

Hi linux-can,

I'm coming from the embedded micro controller end of using CAN and have created
my own CAN Network nodes. Now I'm working with a MCP2515 connected to the
Raspberry Pi, so looking at the Linux Kernel.

On my existing nodes the Initialisation of the CAN device the node either knows
the baudrate to setup or it does not. A node that is a fixed node on the
network knows the baudrate of the network, although this can be changed on the
fly. Other devices are not a fixed part of the network and are connected
dynamically to the network for testing or management purposes. These nodes
don't know the baudrate of the network so automatically detect it. When they
detect the baudrate they then connect and inform the higher application code
that the network is connected, so they can proceed.

I was thinking of adding this auto baudrate detection functionality to the
RaspberryPi but being new to Linux development I'm struggling with whether
this functionality should be in Kernel or User Space. I was initially thinking
User Space but given that numerous applications can be using the CAN Network
you really want to centralise this functionality. That possibly means Kernel
Space?

So before I start to do something I thought I'd ask the experts. Does
automatic baudrate detection belong in Kernel Space or out in Userland? Maybe
it's already in the existing Kernel I've just missed it.

JW

Re: baudrate detection

[Marc Kleine-Budde]

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On 12/12/2013 07:40 PM, John Whitmore wrote:
> I'm coming from the embedded micro controller end of using CAN and have created
> my own CAN Network nodes. Now I'm working with a MCP2515 connected to the
> Raspberry Pi, so looking at the Linux Kernel.

A SPI based CAN adapter like the mcp2515 are known to have bad
performance, you probably will have better CAN experience with an USB
adapter.

> On my existing nodes the Initialisation of the CAN device the node either knows
> the baudrate to setup or it does not. A node that is a fixed node on the
> network knows the baudrate of the network, although this can be changed on the
> fly. Other devices are not a fixed part of the network and are connected
> dynamically to the network for testing or management purposes. These nodes
> don't know the baudrate of the network so automatically detect it. When they
> detect the baudrate they then connect and inform the higher application code
> that the network is connected, so they can proceed.
> 
> I was thinking of adding this auto baudrate detection functionality to the
> RaspberryPi but being new to Linux development I'm struggling with whether
> this functionality should be in Kernel or User Space. I was initially thinking
> User Space but given that numerous applications can be using the CAN Network
> you really want to centralise this functionality. That possibly means Kernel
> Space?
>
> So before I start to do something I thought I'd ask the experts. Does
> automatic baudrate detection belong in Kernel Space or out in Userland? Maybe
> it's already in the existing Kernel I've just missed it.

I think for prototyping the algorithm you should start in userspace, the
you can present it here and then we can discuss if it's better suited in
a library or in the kernel space.

Marc
-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
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