On 17.04.23 09:26, Marc Kleine-Budde wrote:
On 16.04.2023 21:46:40, Oliver Hartkopp wrote:
I had the 5ms that are actually used in the code in mind. But this is a
good calculation.
@Judith: Can you acknowledge the value calculation?
The "shortest" 11 bit CAN ID CAN frame is a Classical CAN frame with DLC = 0
and 1 Mbit/s (arbitration) bitrate. This should be 48 bits @1Mbit => ~50
usecs
So it should be something about
50 usecs * (FIFO queue len - 2)
Where does the "2" come from?
I thought about handling the FIFO earlier than it gets completely "full".
The fetching routine would need some time too and the hrtimer could also
jitter to some extend.
I was assuming something like this.
I would argue that the polling time should be:
50 µs * FIFO length - IRQ overhead.
The max IRQ overhead depends on your SoC and kernel configuration.
I just tried an educated guess to prevent the FIFO to be filled up
completely. How can you estimate the "IRQ overhead"? And how do you
catch the CAN frames that are received while the IRQ is handled?
Best regards,
Oliver
