SK-TDA4VM: Build a Kernel Module to stream bytes over CAN Interface.

Alark Mishra

Part Number: SK-TDA4VM

Hello,

It can seem strange but I am looking to build a kernel module or you can guide me if there is anything present which can fulfil my requirement.

Requirement is:

Build a kernel module that can stream bytes through CAN interface like (can0, can5 and can9).
This streaming of bytes will not follow CAN protocol instead simple transferring of bytes from one physical destination to another.

Why this requirement ?

We have a third party product that is taking UART data over CAN Physical layer (through TJA1044v3 chip) which is basically shifting UART voltage level to CAN differential voltage level. In order to communicate with this either of the methods can be done:

Connect a similar TJA1044V3 interface with SK-TDA4VM and transmit UART data over that, or
Build a kernel module that can transfer UART data (stream of bytes in certain order) over CAN interfaces.

I wish to opt for 2nd method as that will decrease the latency giving us better response time as that is also one requirement of system.

Please let me know how can I proceed with this.

Cordially,
Alark Mishra

over 1 year ago

0 Takuma Fujiwara over 1 year ago

TI__Guru 51823 points

Hi Alark,

TI does not provide a guide for kernel module programming, but there are plenty of kernel development guides online, as the Linux community is very open and helpful. For example, this may be a good documentation to look at: https://www.kernel.org/doc/html/v6.1/process/howto.html.

For CAN specifically, you could reference this FAQ to get started with CAN for SK-TDA4VM: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1132406/faq-sk-tda4vm-how-do-i-use-the-can-bus-headers-on-sk-tda4vm-using-edge-ai-sdk. It's not necessarily a kernel module, but it is an example that uses an userspace application canutils that is used to interface with the CAN driver.

As for the current kernel driver for CAN, you could take a look at the driver code here: https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/drivers/net/can/m_can/m_can_platform.c?h=ti-linux-6.1.y

And device tree can be referenced here: https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/arch/arm64/boot/dts/ti/k3-j721e-main.dtsi?h=ti-linux-6.1.y#n2270, and here: https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/arch/arm64/boot/dts/ti/k3-j721e-sk.dts?h=ti-linux-5.10.y#n203. *Please note the in 6.1 kernel used for TI Processor SDK 9.x, the CAN device tree nodes in k3-j721e-sk.dts has been removed as part of cleaning up the code. These can be added back in by referencing the 5.10 kernel device tree files or you could use the TI PSDK 8.6 which uses the 5.10 kernel.

Although, it may make sense to contact the TJA1044 provider to see if they have an example that you could reference, because it sounds like being able to convert between UART data and CAN data is a key feature of that module.

Regards,

Takuma

0 Alark Mishra over 1 year ago in reply to Takuma Fujiwara

Prodigy 90 points

Hi Takuma,

Thanks for the information !

Yes I am aware about the current CAN implementation and thanks for sharing the CAN driver.

However, when I first tried 9.1 I was not able to find the CAN interface whereas we have it in 5.10 kernel (v8.6 SDK), I have build the yocto-image for 9.1 SDK Linux, I'll try to add the CAN interface in device tree and rebuild the yocto-image.

My concern still lies with building the kernel module and being able to stream bytes over CAN0 interface without sending it packed inside CAN protocol.

Request you to please confirm my understanding:

1. I can insmod the m_can_platform kernel module and operate through the following to send raw bytes over CAN bus ?

.read_reg = iomap_read_reg,
.write_reg = iomap_write_reg,
.write_fifo = iomap_write_fifo,
.read_fifo = iomap_read_fifo,

Also is there need to understand or watchout m_can, can_raw and can drivers, to stream raw bytes over CAN interface ?

Cordially,
Alark Mishra

+1 Takuma Fujiwara over 1 year ago in reply to Alark Mishra

TI__Guru 51823 points

Hi Alark,

I found this E2E that may be of interest: https://e2e.ti.com/support/interface-group/interface/f/interface-forum/929339/what-kind-of-data-send-by-can-bus-transceiver. Reading through, the usecase seems very similar to our usecase where they have some module that simply shifts voltage level between CAN and UART, and it goes through what some limitations are such as losing some CAN protocol related features ("proper data framing, arbitration, error checking, etc").

Otherwise, the CAN driver operates through those functions that you mentioned. But, since the data being received/transmitted is UART, I assume the content of the driver would look more like the serial driver in Linux, so it may make sense to reference that driver: https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/drivers/tty/serial/8250/8250_omap.c?h=ti-linux-6.1.y.

Hopefully this information helps you in your development.

Regards,

Takuma

0 Alark Mishra over 1 year ago in reply to Takuma Fujiwara

Prodigy 90 points

Hello Takuma,

Yeah the above E2E is similar to what I am facing.

I'll try to build a userspace application now that can communicate with m_can_platform driver so that I can stream bytes over CAN interface.

Thanks for the support Takuma !

In any case I'll keep you posted.

Regards,
Alark Mishra

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SK-TDA4VM: Build a Kernel Module to stream bytes over CAN Interface.