how CAN-bus Linux driver MCP251x.c works

[cheng chen]

On Fri, Jan 14, 2011 at 11:28 PM, Dave Hylands <dhylands at gmail.com> wrote:

> Hi Cheng,
>
> On Fri, Jan 14, 2011 at 6:23 AM, cheng chen <freakrobot at acm.org> wrote:
> > I am studying CAN-bus chip Linux driver, MCP251x.c in the kernel source.
> > However, I find a little confused about how this driver works, it
> registers
> > itself as a SPI slave device using the structure
> > struct spi_driver  mcp2510_can_driver = {
> >     .driver = {...}
> >     .probe=
> >     ...
> > }
> > In probe function, it registers itself as a "net_device" with
> > "mcp251x_netdev_ops". So I am not sure how this system works.
> > I know that the userspace must see it as a network driver. But can
> userspace
> > really see this driver? Or what it can see is the module "can.ko" -- the
> > protocol stack ?
> > Does the network stack talks to SPI and SPI talks to mcp2510 chip and
> > transmit messages can-bus? Or something else?
>
> I haven't looked at the code but I have looked at the chip, and I've
> been sort of following along on the Socket-CAN list.
> https://lists.berlios.de/mailman/listinfo/socketcan-users
>
> It would register itself with the network stack, and the network stack
> will expect to send and receive packets. The CAN driver then needs to
> send these packets to the chip over a SPI bus. So it uses the SPI
> infrastructure to send these packets to the actual MCP2510.
>
> Every system has different SPI devices, so this way, the MCP2510
> driver doesn't have to know how the actual SPI layer works, it just
> knows it needs to use the SPI protocol to talk to the MCP2510.
>
> From userspace, you would use the socket API to send you data to
> whatever device you're communicating with via CAN.
>
> So the whole thing should go together something like this:
>
> user space talks to socket API
> network driver talks to CAN driver
> CAN driver talks to SPI driver
> SPI driver talks to SPI hardware
> messages go over the SPI bus to MCP2510
> MCP2510 sends messages over the CAN bus to the actual device
>
> Dave Hylands
>

Thanks for your help, I understand the frameworks now.
But if I want to make the CAN driver(mcp251x.c) works on my own embedded
board, should do some work to make the SPI fit my hardware?

-- 
Cheng(誠)

Fedora Project Contributor -- Ambassador
https://fedoraproject.org/wiki/User:Freakrobot
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My Page: http://freakrobot.blogbus.com/
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