Hi all,
This is a follow up to the SocketCAN integration into NuttX discussion. As
discussed before we proposed the idea to include SocketCAN support in NuttX to
provide a generic well-known interface for CAN transmission. The initial
feedback was great and Gregory Nutt looked into the possibility to integrate
SocketCAN (socket family and legal issues). The other feedback we also got was
about the realtime behavior which might suffer due to SocketCAN. To measure the
impact in realtime behavior I created a testbed using Zephyr RTOS, which
already implemented SocketCAN in their RTOS. The results of this testbed have
been posted here https://forum.uavcan.org/t/socketcan-api-on-a-rtos/750. To
summarize: from the Zephyr SocketCAN I noticed a delay increase from interrupt
to userspace application of ~ 55us and measured jitter didn't increase and
stayed < 0.001us.
I would like gather feedback if 65us is acceptable and if the NuttX network
stack might perform better or worse than that.
Furthermore I've got some questions about some implementation details, below
the figure shows my estimated guess of the current NuttX CAN implementation and
the NuttX Ethernet implementation. If we're going to implement SocketCAN do we
want to support the old NuttX CAN implementation and SocketCAN implementation
at the same time through a single hardware driver? Do people use the NuttX CAN
implementation? Can we implement SocketCAN through the NuttX Ethernet
implementation and completely skip the NuttX CAN implementation?
NuttX CAN Implementation NuttX Ethernet Implementation
+-------------------------------+ +-------------------------------+
| Application | | Application |
+-------------------------------+ +-------------------------------+
+-------------------------------+ +-------------------------------+
| POSIX Interface | | POSIX Interface |
+-------------------------------+ +-------------------------------+
+-------------+ +-------------+ +-------------+ +-------------+
|System calls | |VFS (fs/vfs) | |System calls | |BSD socket |
| | | | | | |net/sockets |
+-------------+ +-------------+ +-------------+ +-------------+
+-------------------------------+ +-------------------------------+
| NuttX CAN Driver (can.c) | | NuttX Network driver |
| +------------+ +------------+ | | +------------+ +------------+ |
| |Syscall glue| |Char driver | | | |Syscall glue| |BSD Socket | |
| | | |glue | | | | | |glue | |
| +------------+ +------------+ | | +------------+ +------------+ |
+-------------------------------+ +-------------------------------+
+-------------------------------+ +-------------------------------+
| Hardware CAN driver | | Hardware MAC driver |
+-------------------------------+ +-------------------------------+
+-------------------------------+ +-------------------------------+
|OS (sched/), memory manager | |OS (sched/), memory manager |
|(mm/), common libraries (libs/)| |(mm/), common libraries (libs/)|
+-------------------------------+ +-------------------------------+
+-------------------------------+ +-------------------------------+
| Hardware | | Hardware |
+-------------------------------+ +-------------------------------+
(Note this is ASCII art use a monospace font to view correctly)
Everything is still a WIP but I would like gather feedback and come up with an
architectural concept for the SocketCAN implementation.
Best regards,
Peter van der Perk
