BBB can bus - no Tx/Rx

Embedded Linux Discussions
1

Hi Robert,

CAN1 is exported to BONE_P9_26/P9_24. the CAN interface is up (listed by ifconfig). No apparent problems on BBBw. But No Rx/Tx.
From


Is device overlay needed for BBBw (4.19.50-ti-r20) ?
On bus, it is properly terminated (60 Ohm).
But, when BBBw CAN1 is connected to P9_26/P9_24, the termination becomes 83Ohm.
BBBw doesn’t have default terminator, right?
Any suggestions that something may have been neglected ?

Thank you,
David

2

Hi @dzhou, so on teh am335x, the can lines must be connected to a bus, otherwise they just don’t work…

If you load the can overlay, the pinmux should be correct.

PS, i still haven’t found a good way to test the can bus in teh lab here, really need to find a cheap can bus emulator/network/tester…

Regards,

3

Hi Robert,

I connected to a CAN bus. I am using PCAN for testing. I also have PCAN-Diag (PEAK). The bus itself is OK. But if connected to CAN1 on BBBw dev board, the termination from 60 Ohm to 80 Ohm. So the BBBw CAN interface has changed termination there.

the am335x_evm.dts has :

	dcan1_pins_default: dcan1_pins_default {
		pinctrl-single,pins = <
			AM33XX_IOPAD(0x968, PIN_OUTPUT | MUX_MODE2) /* uart0_ctsn.d_can1_tx */
			AM33XX_IOPAD(0x96c, PIN_INPUT_PULLDOWN | MUX_MODE2) /* uart0_rtsn.d_can1_rx */
		>;
	};

So, I assume it is already configured. (interface is up and running, no error messages related to CAN1 during initialization).

Thank You,

David

4

as long as you have it enabled thru the node:

&dcan1 {
	status = "okay";
	pinctrl-names = "default";
	pinctrl-0 = <&dcan1_pins_default>;
};

It should be all good.

Regards,

5

Well, in the am335x_evm.dts:

&dcan1 {
	status = "disabled";	/* Enable only if Profile 1 is selected */
	pinctrl-names = "default";
	pinctrl-0 = <&dcan1_pins_default>;
};

It says disabled. Enable only if Profile1 is selected. Don’t know what is the Profile 1. But this status is initial run-time status, right? It can be enabled through configuration without recompiling dtbo?

Also, the P9_26 seems pulled up (high). Is possible the pin mux for P9_26 has a confliction?

Regards,

David

David

6

Then dcan1 is disabled and the pin’s are never pinmux’ed…

Regards,

7

So, I have to rebuild dtbo for (CAN1 only), and update the Linux O/S?

Thank you,

David

8

Yeah, just update your device tree with it enabled.

Regards,