5.5. Frequently Asked Questions

5.5.1. How to verify IPC between Linux and MCU R5 in Keystone devices?

Automotive applications have different memory needs and use a different memory map defined in the auto-common.dtbo file. Therefore, the default Processor SDK is shipped with firmwares for only a few auxiliary cores in the Keystone devices.

Although the out-of-the-box experience does not allow to verify the interprocessor communication (IPC) between Linux and the MCU R5, the following steps describe how this can be done using the SDK.

Steps to build IPC echotest binaries

All the IPC echotest binaries are built as a Yocto package ipc-lld-fw. Since these binaries conflict with the automotive demos, this package is not built in the SDK installed by default. This can be built using Yocto and installed into the filesystem on target.

Make sure that you have setup the Yocto build environment for this. Refer to Building the SDK section for all details.

Once the Yocto build is setup, use bitbake to build the specific package ipc-lld-fw as shown below:

TOOLCHAIN_BASE=<PATH_TO_TOOLCHAIN> MACHINE=<machine> bitbake -k ipc-lld-fw

This will create the firmware package for all the remoteproc cores in the system where the IPC echotest functionality is implemented. The package will be located at the directory <Yocto work directory>/j7_evm-linux/ipc-lld-fw/<version>/deploy-ipks/.

Installing the IPC echotest binaries

Once the package is built on the host machine, copy it to the target filesystem. Run thethe following commands to install the package to target filesystem.

The update-alternatives command in the below instructions will set the priority for the IPC firmware very high. This is to ensure that the symlinks are updated appropriately. Typical firmwares will have priorities up to 20, setting the IPC firmware priority to 100 gives it highest priority.


priority override is done only for the automotive firmwares like ethernet firmware and display sharing firmware. If you have installed additional firmwares, you should do it for others as well.

opkg install ipc-lld-fw*.ipk
update-alternatives --install /lib/firmware/j7-main-r5f0_0-fw j7-main-r5f0_0-fw /lib/firmware/pdk-ipc/ipc_echo_test_mcu2_0_release.strip.xer5f 100
update-alternatives --install /lib/firmware/j7-main-r5f0_1-fw j7-main-r5f0_1-fw /lib/firmware/pdk-ipc/ipc_echo_test_mcu2_1_release.strip.xer5f 100

After this, make sure that all the firmwares are pointing to the pdk-ipc/ version of the binaries by running the following:

ls -l /lib/firmware/j7*

Reboot the board and you will see the IPC echotest binaries loaded onto different CPU cores.

5.5.2. How to configure K3 MSMC memory for use as SRAM or L3 cache?

In Keystone devices, there exists on-chip memory at the MSMC interconnect. This can be configured either as SRAM or as L3 cache.

Automotive ADAS applications, which use C7x, benefit a lot when the MSMC memory is configured as SRAM. Alternatively, the CPU benchmark applications get performance boost when the memory is configured as cache.

Typically, MSMC memory needs to be split between SRAM and cache with the split boundary being aligned at 1MB. System firmware partitions SRAM between cache and SRAM at the bootup based on the board config data structure.

Rebuild the system firmware image (sysfw.itb) with right board config to change to desired behavior. Following are the steps to achieve this:

Modify the file soc/j721e/evm/board-cfg.c in system-firmware-image-gen repo from the installer.

/* boardcfg_msmc */
.msmc = {
        .subhdr = {
                .magic = BOARDCFG_MSMC_MAGIC_NUM,
                .size = sizeof(struct boardcfg_msmc),
        .msmc_cache_size = 0x0,

Here, the msmc_cache_size variable can take values from 0x0 to 0xf, where 0x0 describes zero cache and 0xf describes full cache. Note that due to hardware restriction, the total memory that gets configured as cache is rounded up to 1MB.

Following table describes an example of this for J721e platform.

msmc_cache_size Description
0x0 All of MSMC memory (i.e. 8MB) configured as SRAM
0x3 2MB of MSMC memory configured as cache, rest 6MB is SRAM
0x6 3MB of MSMC memory configured as cache, rest 5MB is SRAM
0xf All of MSMC memory (i.e. 8MB) configured as cache

5.5.3. How to check some device tree information from user-space of Linux?

You might need to check value of some dtb entry, for debugging, checking that your dtb really got updated after you modfified, etc. Though you can’t have a .dts-file-like view of the device tree which was loaded, you can check values using the entries in /proc/device-tree.

In the command prompt of Linux, you should see something similar to the following in the /proc/device-tree directory:

root@j7-evm:~# ls /proc/device-tree/
#address-cells  firmware                l3-cache0
#size-cells     fixedregulator-evm12v0  main_r5fss_cpsw9g_virt_mac0
__symbols__     fixedregulator-sd       memory@80000000
aliases         fixedregulator-vsys3v3  model
chosen          fixedregulator-vsys5v0  name
compatible      gpio-keys               pmu
connector       interconnect@100000     reserved-memory
cpus            interrupt-parent        serial-number
dma_buf_phys    ion                     sound@0
dummy-panel     l2-cache0               timer-cl0-cpu0

Following are some typical usages you might need:

  • Let’s say you don’t know the exact path of the device tree entry you are trying to check. There is a __symbol__ directory in /proc/device-tree, which is very helpful in such cases. It has an entry for each symbol label in the device tree. You can find the exact path for that symbol by running cat command on that entry. Following is an example demonstrating the use:

    root@j7-evm:~# cat /proc/device-tree/__symbols__/main_i2c0
    root@j7-evm:~# ls /proc/device-tree/interconnect@100000/i2c@2000000/
    #address-cells   clock-names  gpio@20     name       pinctrl-names
    #size-cells      clocks       gpio@22     phandle    power-domains
    clock-frequency  compatible   interrupts  pinctrl-0  reg
  • You can check the value of a device tree entry using cat command if it is a string. But if the value is an integer or some numeric data, you will have to run the xxd command instead of cat, to get output in a readable format. Following is an example demonstrating the use:

    # Example for a string value
    root@j7-evm:~# cat /proc/device-tree/interconnect@100000/i2c@2000000/compatible
    # Example for an integer value
    root@j7-evm:~# xxd -g4 /proc/device-tree/interconnect@100000/i2c@2000000/clock-frequency
    00000000: 00061a80                             ....
    # The above value is in hexadecimal. You can calculate it's value in decimal by using following command
    root@j7-evm:~# echo $((0x00061a80))
  • One common scenario of a device tree change is tweaking the memory for remoteproc processors like R5F. You can check if it got updated correctly, by running a command similar to following for the specific processor core.

    # Finding symbols for R5Fs
    root@j7-evm:~# ls /proc/device-tree/__symbols__/main_r5fss*
    /proc/device-tree/__symbols__/main_r5fss0                          /proc/device-tree/__symbols__/main_r5fss0_core1_dma_memory_region  /proc/device-tree/__symbols__/main_r5fss1_core0_memory_region
    /proc/device-tree/__symbols__/main_r5fss0_core0                    /proc/device-tree/__symbols__/main_r5fss0_core1_memory_region      /proc/device-tree/__symbols__/main_r5fss1_core1
    /proc/device-tree/__symbols__/main_r5fss0_core0_dma_memory_region  /proc/device-tree/__symbols__/main_r5fss1                          /proc/device-tree/__symbols__/main_r5fss1_core1_dma_memory_region
    /proc/device-tree/__symbols__/main_r5fss0_core0_memory_region      /proc/device-tree/__symbols__/main_r5fss1_core0                    /proc/device-tree/__symbols__/main_r5fss1_core1_memory_region
    /proc/device-tree/__symbols__/main_r5fss0_core1                    /proc/device-tree/__symbols__/main_r5fss1_core0_dma_memory_region
    # Finding location from the symbols
    root@j7-evm:~# cat /proc/device-tree/__symbols__/main_r5fss0_core0_memory_region
    root@j7-evm:~# cat /proc/device-tree/__symbols__/main_r5fss0_core0_dma_memory_region
    # Checking the values
    root@j7-evm:~# xxd -g4 /proc/device-tree/reserved-memory/r5f-memory@a2100000/reg
    00000000: 00000000 a2100000 00000000 01f00000  ................
    root@j7-evm:~# xxd -g4 /proc/device-tree/reserved-memory/r5f-dma-memory@a2000000/reg
    00000000: 00000000 a2000000 00000000 00100000  ................