Re: API to support hardware priorities

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 11/09/2015 04:27 PM, Benedikt Spranger wrote:
>> Do you mean the mailbox feature, where you queue a frame into
>> hardware, but sending is delayed until a certain CAN-ID is RX'ed?
> No.
> The C-CAN/D-CAN and some other Controller can be configured to have
> mailboxes for a certain Id. For example you can configure MBX 1 for
> Id 23, MBX 2 for Id 42 and 3-7 act as FIFO. So every packet matching Id
> 23 should queued up to MBX 1, every package matching Id 42 to MBX 2 and
> all other Packages to the FIFO.

OK, I was not aware of that feature. I'll have a look to the datasheets.
What's the benefit of associating a mailbox to a specific ID in the
hardware?

> Having a multiqueue TX part may help but may have some drawbacks. If the
> FIFO (or an other queue) is full the driver calls netif_stop_queue().

In this scenario there will be two netif_queues per CAN driver....

> Sending bulk data can block out a "high priority" Package. On the other
> hand a application writing bulk data in blocking mode should not
> receive a EAGAIN and not be punished by a "mixed up" queue i.e.
> violating the package send order.

...one serving the bulk hardware FIFO and one serving the high prio HW
queue.

Marc

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