4. IPC for AM64x

The AM64x processor has up to two Dual-Core Cortex-R5F subsystems (R5FSS), and a Cortex-M4F subsystem, in addition to a Dual core Cortex-A53 subsystem. The R5FSS can be operated in dual core mode (i.e., Split mode), or single core mode (i.e., Single-CPU mode). Please refer to the AM64x Technical Reference Manual for details.

This article is geared toward AM64x users that are running Linux on the Cortex A53 cores. The goal is to help users understand how to establish communication with the R5F and M4F cores.

There are many facets to this task: building, loading, debugging, memory sharing, etc. This article intends to take incremental steps toward understanding all of those pieces.

4.1. Software Dependencies to Get Started



Please be sure that you have the same version number for both Processor SDK RTOS and Linux.

Please refer to the MCU+SDK IPC documentation for R5F and M4F IPC architecture and builds:

4.2. Typical Boot Flow on AM64x for ARM Linux users

AM64x SOC’s have multiple processor cores - Cortex-A53, Cortex-R5F, and Cortex-M4F ARM cores. The A53 typically runs a HLOS like Linux/Android. The remote cores (R5Fs and M4F) run No-OS or RTOS (FreeRTOS etc). In normal operation, the boot loader (U-Boot/SPL) boots and loads the A53 with the HLOS. The A53 then boots the R5 and M4F cores.



Please note early boot is not yet supported on AM64x devices.

4.3. Getting Started with IPC Linux Examples

The figure below illustrates how the Remoteproc/RPMsg driver from the ARM Linux kernel communicates with the IPC driver on a remote processor (e.g. R5F) running RTOS.


In order to setup IPC on remote cores, we provide some pre-built examples in the SDK package that can be run from ARM Linux.

The remoteproc driver is hard-coded to look for specific files when loading the R5F cores. Here are the files it looks on AM64x device:

| Core Name        | RemoteProc Name | Description        | Firmware File Name   |
| R5F0-0           | 78000000.r5f    | R5F cluster0-Core0 | am64-main-r5f0_0-fw  |
| R5F0-1           | 78200000.r5f    | R5F cluster0-Core1 | am64-main-r5f0_1-fw  |
| R5F1-0           | 78400000.r5f    | R5F cluster1-Core0 | am64-main-r5f1_0-fw  |
| R5F1-1           | 78600000.r5f    | R5F cluster1-Core1 | am64-main-r5f1_1-fw  |
| M4F              | 5000000.m4f     | M4F core           | am64-mcu-m4f0_0-fw   |

Generally on a target file system the above files are soft linked to the intended executable FW files.:

root@am64xx-evm:~# ls -l /lib/firmware
lrwxrwxrwx 1 root root      55 Jan  9  2022 am64-main-r5f0_0-fw -> /lib/firmware/mcusdk-benchmark_demo/am64-main-r5f0_0-fw
lrwxrwxrwx 1 root root      55 Jan  9  2022 am64-main-r5f0_1-fw -> /lib/firmware/mcusdk-benchmark_demo/am64-main-r5f0_1-fw
lrwxrwxrwx 1 root root      55 Jan  9  2022 am64-main-r5f1_0-fw -> /lib/firmware/mcusdk-benchmark_demo/am64-main-r5f1_0-fw
lrwxrwxrwx 1 root root      55 Jan  9  2022 am64-main-r5f1_1-fw -> /lib/firmware/mcusdk-benchmark_demo/am64-main-r5f1_1-fw
lrwxrwxrwx 1 root root      72 Jan  9  2022 am64-mcu-m4f0_0-fw -> /lib/firmware/pdk-ipc/ipc_echo_baremetal_test_mcu3_0_release_strip.xer5f

4.4. Booting Remote Cores from Linux console/User space

To reload a remote core with new executables, please follow the below steps.

First, identify the remotproc node associated with the remote core:

root@am64xx-evm:~# head /sys/class/remoteproc/remoteproc*/name
==> /sys/class/remoteproc/remoteproc0/name <==

==> /sys/class/remoteproc/remoteproc1/name <==

==> /sys/class/remoteproc/remoteproc2/name <==

==> /sys/class/remoteproc/remoteproc3/name <==

==> /sys/class/remoteproc/remoteproc4/name <==

Then, use the sysfs interface to stop the remote core. For example, to stop R5F cluster0-Core0:

root@am64xx-evm:~# echo stop > /sys/class/remoteproc/remoteproc1/state
[  778.963928] remoteproc remoteproc1: stopped remote processor 78000000.r5f

If needed, update the firmware symbolic link to point to a new firmware:

root@am64xx-evm:~# ln -sf /lib/firmware/pdk-ipc/ipc_echo_baremetal_test_mcu1_0_release_strip.xer5f am64-main-r5f0_0-fw

Finally, use the sysfs interface to start the remote core:

root@am64xx-evm:~# echo start > /sys/class/remoteproc/remoteproc1/state
[ 1141.491165] remoteproc remoteproc1: powering up 78000000.r5f
[ 1141.497109] remoteproc remoteproc1: Booting fw image am64-main-r5f0_0-fw, size 86352
[ 1141.507920]  remoteproc1#vdev0buffer: assigned reserved memory node r5f-dma-memory@a0000000
[ 1141.518539] virtio_rpmsg_bus virtio1: rpmsg host is online
[ 1141.525859] virtio_rpmsg_bus virtio1: creating channel rpmsg_chrdev addr 0xe
[ 1141.536806]  remoteproc1#vdev0buffer: registered virtio1 (type 7)
[ 1141.544195] remoteproc remoteproc1: remote processor 78000000.r5f is now up


The RemoteProc driver does not support a graceful shutdown of R5 and M4 cores in the current Linux Processor SDK. For now, it is recommended to reboot the board when loading new binaries into an R5F or M4F core.

4.5. DMA memory Carveouts

System memory is carved out for each remote processor core for IPC and for the remote processor’s code/data section needs. The default memory carveouts (DMA pools) are shown below.

The default DMA pools assume that the R5F subsystems are operating in Split mode. If an R5F subsystem is run in Single-CPU mode, then R5F Core0 continues to use memory carveouts. However, R5F Core1 is unused in Single-CPU mode, so the Core1 memory carveouts can be reallocated to other cores. See the devicetree bindings documentation for more details: Documentation/devicetree/bindings/remoteproc/ti,k3-r5f-rproc.yaml

| Memory Section   | Physical Address   | Size    | Description                |
| R5F0-0 Pool      | 0xa0000000         | 1MB     | IPC (Virtio/Vring buffers) |
| R5F0-0 Pool      | 0xa0100000         | 15MB    | R5F externel code/data mem |
| R5F0-1 Pool      | 0xa1000000         | 1MB     | IPC (Virtio/Vring buffers) |
| R5F0-1 Pool      | 0xa1100000         | 15MB    | R5F externel code/data mem |
| R5F1-0 Pool      | 0xa2000000         | 1MB     | IPC (Virtio/Vring buffers) |
| R5F1-0 Pool      | 0xa2100000         | 15MB    | R5F externel code/data mem |
| R5F1-1 Pool      | 0xa3000000         | 1MB     | IPC (Virtio/Vring buffers) |
| R5F1-1 Pool      | 0xa3100000         | 15MB    | R5F externel code/data mem |
| M4F Pool         | 0xa4000000         | 1MB     | IPC (Virtio/Vring buffers) |
| M4F Pool         | 0xa4100000         | 15MB    | M4F externel code/data mem |

root@am64xx-evm:~# dmesg | grep 'Reserved'
[    0.000000] Reserved memory: created DMA memory pool at 0x00000000a0100000, size 15 MiB
[    0.000000] Reserved memory: created DMA memory pool at 0x00000000a1000000, size 1 MiB
[    0.000000] Reserved memory: created DMA memory pool at 0x00000000a1100000, size 15 MiB
[    0.000000] Reserved memory: created DMA memory pool at 0x00000000a2000000, size 1 MiB
[    0.000000] Reserved memory: created DMA memory pool at 0x00000000a2100000, size 15 MiB
[    0.000000] Reserved memory: created DMA memory pool at 0x00000000a3000000, size 1 MiB
[    0.000000] Reserved memory: created DMA memory pool at 0x00000000a3100000, size 15 MiB
[    0.000000] Reserved memory: created DMA memory pool at 0x00000000a4000000, size 1 MiB
[    0.000000] Reserved memory: created DMA memory pool at 0x00000000a4100000, size 15 MiB

By default the first 1MB of each pool is used for the Virtio and Vring buffers used to communicate with the remote processor core. The remaining 15MB of the carveout is used for the remote core external memory (program code, data, etc).


The resource table entity (which describes the system resources needed by the remote processor) needs to be at the beginning of the 15MB remote processor external memory section.

For details on how to adjust the sizes and locations of the remote core pool carveouts, please see section Changing the Memory Map.

4.6. Changing the Memory Map

The address and size of the DMA memory carveouts needs to match with the MCU (R5F & M4F) external memory section sizes in their linker mapfiles.


reserved-memory {
                #address-cells = <2>;
                #size-cells = <2>;

main_r5fss0_core0_dma_memory_region: r5f-dma-memory@a0000000 {
        compatible = "shared-dma-pool";
        reg = <0x00 0xa0000000 0x00 0x100000>;

main_r5fss0_core0_memory_region: r5f-memory@a0100000 {
        compatible = "shared-dma-pool";
        reg = <0x00 0xa0100000 0x00 0xf00000>;

main_r5fss0_core1_dma_memory_region: r5f-dma-memory@a1000000 {
        compatible = "shared-dma-pool";
        reg = <0x00 0xa1000000 0x00 0x100000>;

main_r5fss0_core1_memory_region: r5f-memory@a1100000 {
        compatible = "shared-dma-pool";
        reg = <0x00 0xa1100000 0x00 0xf00000>;

main_r5fss1_core0_dma_memory_region: r5f-dma-memory@a2000000 {
        compatible = "shared-dma-pool";
        reg = <0x00 0xa2000000 0x00 0x100000>;

main_r5fss1_core0_memory_region: r5f-memory@a2100000 {
        compatible = "shared-dma-pool";
        reg = <0x00 0xa2100000 0x00 0xf00000>;

main_r5fss1_core1_dma_memory_region: r5f-dma-memory@a3000000 {
        compatible = "shared-dma-pool";
        reg = <0x00 0xa3000000 0x00 0x100000>;

main_r5fss1_core1_memory_region: r5f-memory@a3100000 {
        compatible = "shared-dma-pool";
        reg = <0x00 0xa3100000 0x00 0xf00000>;

mcu_m4fss_dma_memory_region: m4f-dma-memory@a4000000 {
        compatible = "shared-dma-pool";
        reg = <0x00 0xa4000000 0x00 0x100000>;

mcu_m4fss_memory_region: m4f-memory@a4100000 {
        compatible = "shared-dma-pool";
        reg = <0x00 0xa4100000 0x00 0xf00000>;

rtos_ipc_memory_region: ipc-memories@a5000000 {
        reg = <0x00 0xa5000000 0x00 0x00800000>;
        alignment = <0x1000>;


Be careful not to overlap carveouts!

4.7. RPMsg Char Driver

The below picture depicts the kernel driver components and the user space device model for using RPMsg Char driver for communicating with the remote processor.


The RPMsg char driver exposes RPMsg endpoints to user-space processes. Multiple user-space applications can use one RPMsg device uniquely by requesting different interactions with the remote service. The RPMsg char driver supports the creation of multiple endpoints for each probed RPMsg char device, enabling the use of the same device for different instances.

RPMsg devices

Each created endpoint device shows up as a single character device in /dev.

The RPMsg bus sits on top of the VirtIO bus. Each virtio name service announcement message creates a new RPMsg device, which is supposed to bind to a RPMsg driver. RPMsg devices are created dynamically:

The remote processor announces the existence of a remote RPMsg service by sending a name service announcement message containing the name of the service (i.e. name of the device), source and destination addresses. The message is handled by the RPMsg bus, which dynamically creates and registers an RPMsg device which represents the remote service. As soon as a relevant RPMsg driver is registered, it is immediately probed by the bus and the two sides can start exchanging messages.

The control interface

The RPMsg char driver provides control interface (in the form of a character device under /dev/rpmsg_ctrlX) allowing user-space to export an endpoint interface for each exposed endpoint. The control interface provides a dedicated ioctl to create an endpoint device.

4.8. ti-rpmsg-char library

The ti-rpmsg-char package is located at the ti-rpmsg-char git repo <https://git.ti.com/cgit/rpmsg/ti-rpmsg-char>.

A thin userspace rpmsg char library is provided. The library abstracts the rpmsg char driver usage from userspace. This library provides an easy means to identify and open rpmsg character devices created by the kernel rpmsg-char driver.

This library support TI K3 family of devices (i.e AM65x, AM64x, J721E, and J7200 SoCs).

The library provides 4 basic APIs wrapping all the rpmsg char driver calls. Please check documentation in ‘include/ti_rpmsg_char.h’ for details..

This function checks that the needed kernel drivers (remoteproc. rpmsg, virtio) are installed and accessible from the user space. Further it also checks the SoC device supports the requested remote processor.
This function finalizes and performs all the de-initialization and any cleanup on the library. This is the last function that needs to be invoked after all usage is done as part of the application’s cleanup. This only need to be invoked once in an application, there is no reference counting. The function also needs to be invoked in any application’s signal handlers to perform the necessary cleanup of stale rpmsg endpoint devices.
Function to create and access a rpmsg endpoint device for a given rpmsg device.
Function to close and delete a previously created local endpoint

All remote proc ids are defined in rproc_id.h

The below table lists the device enumerations as defined in the rpmsg_char_library. The validiaty of the enumerations wrt AM64x is also specified.

| Enumeration ID   | Device Name        | Valid   | Description                       |
| R5F_MCU0_0       |N/A                 | No      | R5F SS in MCU domain              |
| R5F_MCU0_1       |N/A                 | No      | R5F SS in MCU domain              |
| R5F_MAIN0_0      | 78000000.r5f       | Yes     | R5F Cluster0 Core0 in Main Domain |
| R5F_MAIN0_1      | 78200000.r5f       | Yes     | R5F Cluster0 Core1 in Main Domain |
| R5F_MAIN1_0      | 78400000.r5f       | Yes     | R5F Cluster1 Core0 in Main Domain |
| R5F_MAIN1_1      | 78600000.r5f       | Yes     | R5F Cluster1 Core1 in Main Domain |
| DSP_C66_0        |N/A                 | No      | C66 DSP                           |
| DSP_C66_1        |N/A                 | No      | C66 DSP                           |
| DSP_C71_0        |N/A                 | No      | C71 DSP                           |
| M4F_MCU0_0       | 5000000.m4f        | Yes     | M4F core in MCU Domain            |


The R5F clusters on AM64x can be in either single core or dual core mode. In single core mode enumerations ‘R5F_MAIN0_1 and R5F_MAIN1_1’ are not valid.

4.9. RPMsg examples:

RPMsg user space example


These steps were tested on Ubuntu 18.04. Later versions of Ubuntu may need different steps

Access source code in the git repo here <https://git.ti.com/cgit/rpmsg/ti-rpmsg-char>. rproc_id is defined at include/rproc_id.h <https://git.ti.com/cgit/rpmsg/ti-rpmsg-char/tree/include/rproc_id.h>.

Build the Linux Userspace example for Linux RPMsg by following the steps in the top-level README:

  1. Download the git repo
  2. Install GNU autoconf, GNU automake, GNU libtool, and v8 compiler as per the README
  3. Perform the Build Steps as per the README

Linux RPMsg can be tested with prebuilt binaries that are packaged in the “tisdk-default-image-am64xx-evm” filesystem:

  1. Copy the Linux RPMsg Userspace application from <ti-rpmsg-char_repo>/examples/rpmsg_char_simple into the board’s Linux filesystem.
  2. Ensure that the remote core symbolic link points to the desired binary file in /lib/firmware/pdk-ipc/. Update the symbolic link if needed. Reference section Booting Remote Cores from Linux console/User space for more information.
  3. Run the example on the board:
Usage: rpmsg_char_simple [-r <rproc_id>] [-n <num_msgs>] [-d <rpmsg_dev_name] [-p <remote_endpt]
                Defaults: rproc_id: 0 num_msgs: 100 rpmsg_dev_name: NULL remote_endpt: 14

root@am64xx-evm:~# rpmsg_char_simple -r 2 -n 10
Created endpt device rpmsg-char-2-1027, fd = 3 port = 1025
Exchanging 10 messages with rpmsg device ti.ipc4.ping-pong on rproc id 2 ...

Sending message #0: hello there 0!
Receiving message #0: hello there 0!
Sending message #1: hello there 1!
Receiving message #1: hello there 1!
Sending message #2: hello there 2!
Receiving message #2: hello there 2!
Sending message #3: hello there 3!
Receiving message #3: hello there 3!
Sending message #4: hello there 4!
Receiving message #4: hello there 4!
Sending message #5: hello there 5!
Receiving message #5: hello there 5!
Sending message #6: hello there 6!
Receiving message #6: hello there 6!
Sending message #7: hello there 7!
Receiving message #7: hello there 7!
Sending message #8: hello there 8!
Receiving message #8: hello there 8!
Sending message #9: hello there 9!
Receiving message #9: hello there 9!

Communicated 10 messages successfully on rpmsg-char-2-1027

RPMsg kernel space example

The kernel space example is in the Linux Processor SDK under samples/rpmsg/rpmsg_client_sample.c

Build the kernel module rpmsg_client_sample:

  1. Set up the kernel config to build the rpmsg client sample. Use menuconfig to verify Kernel hacking > Sample kernel code > Build rpmsg client sample is M:
$ export PATH=<sdk path>/linux-devkit/sysroots/x86_64-arago-linux/usr/bin:$PATH
$ make ARCH=arm64 CROSS_COMPILE=aarch64-none-linux-gnu- distclean
$ make ARCH=arm64 CROSS_COMPILE=aarch64-none-linux-gnu- tisdk_am64xx-evm_defconfig
$ make ARCH=arm64 CROSS_COMPILE=aarch64-none-linux-gnu- menuconfig
  1. Make the kernel and modules. Multithreading with –j is optional:
$ make ARCH=arm64 CROSS_COMPILE=aarch64-none-linux-gnu- -j8

Linux RPMsg can be tested with prebuilt binaries that are packaged in the “tisdk-default-image-am64xx-evm” filesystem:

  1. Copy the Linux RPMsg kernel driver from <Linux_SDK>/board-support/linux-x.x.x/samples/rpmsg/rpmsg_client_sample.ko into the board’s Linux filesystem.
  2. Ensure that the remote core symbolic link points to the desired binary file in /lib/firmware/pdk-ipc/. Update the symbolic link if needed. Reference section Booting Remote Cores from Linux console/User space for more information.
  3. Run the example on the board:
root@am64xx-evm:~# modprobe rpmsg_client_sample count=10
[  192.754123] rpmsg_client_sample virtio0.ti.ipc4.ping-pong.-1.13: new channel: 0x400 -> 0xd!
[  192.762614] rpmsg_client_sample virtio0.ti.ipc4.ping-pong.-1.13: incoming msg 1 (src: 0xd)
[  192.767945] rpmsg_client_sample virtio1.ti.ipc4.ping-pong.-1.13: new channel: 0x400 -> 0xd!
[  192.778102] rpmsg_client_sample virtio0.ti.ipc4.ping-pong.-1.13: incoming msg 2 (src: 0xd)
[  192.787125] rpmsg_client_sample virtio2.ti.ipc4.ping-pong.-1.13: new channel: 0x400 -> 0xd!
[  192.793103] rpmsg_client_sample virtio0.ti.ipc4.ping-pong.-1.13: incoming msg 3 (src: 0xd)
[  192.799752] rpmsg_client_sample virtio3.ti.ipc4.ping-pong.-1.13: new channel: 0x400 -> 0xd!
[  192.809324] rpmsg_client_sample virtio0.ti.ipc4.ping-pong.-1.13: incoming msg 4 (src: 0xd)
[  192.823064] rpmsg_client_sample virtio0.ti.ipc4.ping-pong.-1.13: incoming msg 5 (src: 0xd)
[  192.833132] rpmsg_client_sample virtio0.ti.ipc4.ping-pong.-1.13: incoming msg 6 (src: 0xd)
[  192.843179] rpmsg_client_sample virtio0.ti.ipc4.ping-pong.-1.13: incoming msg 7 (src: 0xd)
[  192.853170] rpmsg_client_sample virtio0.ti.ipc4.ping-pong.-1.13: incoming msg 8 (src: 0xd)
[  192.863228] rpmsg_client_sample virtio0.ti.ipc4.ping-pong.-1.13: incoming msg 9 (src: 0xd)
[  192.873335] rpmsg_client_sample virtio0.ti.ipc4.ping-pong.-1.13: incoming msg 10 (src: 0xd)
[  192.883392] rpmsg_client_sample virtio0.ti.ipc4.ping-pong.-1.13: goodbye!
[  192.891964] rpmsg_client_sample virtio1.ti.ipc4.ping-pong.-1.13: incoming msg 1 (src: 0xd)
[  192.902022] rpmsg_client_sample virtio1.ti.ipc4.ping-pong.-1.13: incoming msg 2 (src: 0xd)
[  192.912136] rpmsg_client_sample virtio1.ti.ipc4.ping-pong.-1.13: incoming msg 3 (src: 0xd)
[  192.922181] rpmsg_client_sample virtio1.ti.ipc4.ping-pong.-1.13: incoming msg 4 (src: 0xd)
[  192.932270] rpmsg_client_sample virtio1.ti.ipc4.ping-pong.-1.13: incoming msg 5 (src: 0xd)
[  192.942319] rpmsg_client_sample virtio1.ti.ipc4.ping-pong.-1.13: incoming msg 6 (src: 0xd)
[  192.952403] rpmsg_client_sample virtio1.ti.ipc4.ping-pong.-1.13: incoming msg 7 (src: 0xd)
[  192.962433] rpmsg_client_sample virtio1.ti.ipc4.ping-pong.-1.13: incoming msg 8 (src: 0xd)
[  192.972538] rpmsg_client_sample virtio1.ti.ipc4.ping-pong.-1.13: incoming msg 9 (src: 0xd)
[  192.982616] rpmsg_client_sample virtio1.ti.ipc4.ping-pong.-1.13: incoming msg 10 (src: 0xd)
[  192.992836] rpmsg_client_sample virtio1.ti.ipc4.ping-pong.-1.13: goodbye!
[  193.001472] rpmsg_client_sample virtio2.ti.ipc4.ping-pong.-1.13: incoming msg 1 (src: 0xd)
[  193.011614] rpmsg_client_sample virtio2.ti.ipc4.ping-pong.-1.13: incoming msg 2 (src: 0xd)
[  193.020184] rpmsg_client_sample virtio2.ti.ipc4.ping-pong.-1.13: incoming msg 3 (src: 0xd)
[  193.028628] rpmsg_client_sample virtio2.ti.ipc4.ping-pong.-1.13: incoming msg 4 (src: 0xd)
[  193.037089] rpmsg_client_sample virtio2.ti.ipc4.ping-pong.-1.13: incoming msg 5 (src: 0xd)
[  193.045484] rpmsg_client_sample virtio2.ti.ipc4.ping-pong.-1.13: incoming msg 6 (src: 0xd)
[  193.053874] rpmsg_client_sample virtio2.ti.ipc4.ping-pong.-1.13: incoming msg 7 (src: 0xd)
[  193.062261] rpmsg_client_sample virtio2.ti.ipc4.ping-pong.-1.13: incoming msg 8 (src: 0xd)
[  193.070614] rpmsg_client_sample virtio2.ti.ipc4.ping-pong.-1.13: incoming msg 9 (src: 0xd)
[  193.079000] rpmsg_client_sample virtio2.ti.ipc4.ping-pong.-1.13: incoming msg 10 (src: 0xd)
[  193.087397] rpmsg_client_sample virtio2.ti.ipc4.ping-pong.-1.13: goodbye!
[  193.094355] rpmsg_client_sample virtio3.ti.ipc4.ping-pong.-1.13: incoming msg 1 (src: 0xd)
[  193.102729] rpmsg_client_sample virtio3.ti.ipc4.ping-pong.-1.13: incoming msg 2 (src: 0xd)
[  193.111134] rpmsg_client_sample virtio3.ti.ipc4.ping-pong.-1.13: incoming msg 3 (src: 0xd)
[  193.119512] rpmsg_client_sample virtio3.ti.ipc4.ping-pong.-1.13: incoming msg 4 (src: 0xd)
[  193.127928] rpmsg_client_sample virtio3.ti.ipc4.ping-pong.-1.13: incoming msg 5 (src: 0xd)
[  193.136292] rpmsg_client_sample virtio3.ti.ipc4.ping-pong.-1.13: incoming msg 6 (src: 0xd)
[  193.144761] rpmsg_client_sample virtio3.ti.ipc4.ping-pong.-1.13: incoming msg 7 (src: 0xd)
[  193.153207] rpmsg_client_sample virtio3.ti.ipc4.ping-pong.-1.13: incoming msg 8 (src: 0xd)
[  193.161691] rpmsg_client_sample virtio3.ti.ipc4.ping-pong.-1.13: incoming msg 9 (src: 0xd)
[  193.170119] rpmsg_client_sample virtio3.ti.ipc4.ping-pong.-1.13: incoming msg 10 (src: 0xd)
[  193.178632] rpmsg_client_sample virtio3.ti.ipc4.ping-pong.-1.13: goodbye!