cannot bring up /dev/rpmsg_pru31 with rpmsg_pru

I am trying the PRU_RPMsg_Echo_Interrupt1 example in pru-software-support-package with BeagleBone Black. The code builds ok. It was successfully loaded and started on PRU1. The state under /sys/class/remoteproc/remoteproc2 shows “running”.

However, when I start the rpmsg_pru, I am not getting the expected message in dmesg like " new rpmsg_pru device: /dev/rpmsg_pru31 ", and of course, rpmsg_pru31 was not created under /dev.

Below is the dmesg I am getting:

[   78.045391] pruss 4a300000.pruss: creating PRU cores and other child platform devices
[   78.126593] remoteproc remoteproc1: 4a334000.pru is available
[   78.126717] pru-rproc 4a334000.pru: PRU rproc node /ocp/pruss_soc_bus@4a326004/pruss@0/pru@34000 probed successfully
[   78.137710] remoteproc remoteproc2: 4a338000.pru is available
[   78.137836] pru-rproc 4a338000.pru: PRU rproc node /ocp/pruss_soc_bus@4a326004/pruss@0/pru@38000 probed successfully
[  366.901804] remoteproc remoteproc2: powering up 4a338000.pru
[  366.911257] remoteproc remoteproc2: Booting fw image am335x-pru1-fw, size 78140
[  366.911887] pruss 4a300000.pruss: configured system_events[63-0] = 0x08000000.00000000
[  366.911901] pruss 4a300000.pruss: configured intr_channels = 0x00000002 host_intr = 0x00000002
[  366.914522] remoteproc remoteproc2: registered virtio0 (type 7)
[  366.914538] remoteproc remoteproc2: remote processor 4a338000.pru is now up
[  366.983900] virtio_rpmsg_bus virtio0: rpmsg host is online

and lsmod result