[FAQ] AM62x & AM64x: How to enable PRU RPMsg on Processor SDK Linux 11.0

Step 1: Patch the Linux kernel driver 

a) Apply kernel driver patch "remoteproc: pru: Add support for virtio rpmsg stack":
https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/patch/?id=f21a9eb2166ca69563deb32980fde16800c7e77a

b) rebuild the kernel image & kernel modules, as described in sections
Preparing to Build
Configuring the Kernel
Compiling the Sources
https://software-dl.ti.com/processor-sdk-linux/esd/AM62X/latest/exports/docs/linux/Foundational_Components_Kernel_Users_Guide.html 

c) install the kernel image & kernel modules, as described in section
Installing the Kernel
https://software-dl.ti.com/processor-sdk-linux/esd/AM62X/latest/exports/docs/linux/Foundational_Components_Kernel_Users_Guide.html#installing-the-kernel

Step 2: Update the PRU firmware 

The generic Linux RPMsg driver uses a different channel name (rpmsg-raw) than the previous PRU RPMsg driver (rpmsg-pru). Update the PRU firmware to use rpmsg-raw.

The latest PRU Software Support Package (PSSP) can be downloaded from here:
https://git.ti.com/cgit/pru-software-support-package/pru-software-support-package/

PSSP v6.5.0 will update all firmware to use rpmsg-raw.

If PSSP v6.5.0 is not released at the time you are reading this FAQ, you can update your PRU firmware like this:

diff --git a/examples/am64x/PRU_RPMsg_Echo_Interrupt0/main.c b/examples/am64x/PRU_RPMsg_Echo_Interrupt0/main.c
index f467eed..a8ee63a 100644
--- a/examples/am64x/PRU_RPMsg_Echo_Interrupt0/main.c
+++ b/examples/am64x/PRU_RPMsg_Echo_Interrupt0/main.c
@@ -55,7 +55,7 @@ volatile register uint32_t __R31;
* Using the name 'rpmsg-pru' will probe the rpmsg_pru driver found
* at linux-x.y.z/drivers/rpmsg/rpmsg_pru.c
*/
-#define CHAN_NAME "rpmsg-pru"
+#define CHAN_NAME "rpmsg-raw"
#ifndef CHAN_PORT
#error "CHAN_PORT not defined, must be passed using the compiler CFLAGS"
#endif

Step 3: Run the PRU RPMsg Echo example 

Copy the updated firmware into the EVM filesystem 

For example,

AM62x example

// remove or rename the firmware from before PSSP v6.5.0
root@am62xx-evm:~# ls -al /lib/firmware/
...
lrwxrwxrwx  1 root root      51 Mar  9  2018 am62x-pru0-fw -> /usr/lib/firmware/pru/PRU_RPMsg_Echo_Interrupt0.out
lrwxrwxrwx  1 root root      51 Mar  9  2018 am62x-pru1-fw -> /usr/lib/firmware/pru/PRU_RPMsg_Echo_Interrupt1.out

root@am62xx-evm:~# cd /usr/lib/firmware/pru/
root@am62xx-evm:/usr/lib/firmware/pru# ls
PRU_Halt.out  PRU_RPMsg_Echo_Interrupt0.out  PRU_RPMsg_Echo_Interrupt1.out
root@am62xx-evm:/usr/lib/firmware/pru# mv PRU_RPMsg_Echo_Interrupt0.out PRU_RPMsg_Echo_Interrupt0.out.v6_4_0
root@am62xx-evm:/usr/lib/firmware/pru# mv PRU_RPMsg_Echo_Interrupt1.out PRU_RPMsg_Echo_Interrupt1.out.v6_4_0

// then copy the updated firmware into this location

Figure out which PRU core is associated with which remoteprocX instance 

// find which PRU core you want to connect to
// remoteprocX association can change each boot, so use the name to determine
// which core is which
root@am62xx-evm:/sys/devices# head /sys/class/remoteproc/remoteproc*/name
...
==> /sys/class/remoteproc/remoteproc2/name <==
30074000.pru

==> /sys/class/remoteproc/remoteproc3/name <==
30078000.pru


// now let's verify that we will load the updated firmware
root@am62xx-evm:/sys/devices# cat /sys/class/remoteproc/remoteproc3/firmware
am62x-pru1-fw

root@am62xx-evm:/sys/devices# ls -al /lib/firmware
...
lrwxrwxrwx  1 root root      51 Mar  9  2018 am62x-pru0-fw -> /usr/lib/firmware/pru/PRU_RPMsg_Echo_Interrupt0.out
lrwxrwxrwx  1 root root      51 Mar  9  2018 am62x-pru1-fw -> /usr/lib/firmware/pru/PRU_RPMsg_Echo_Interrupt1.out

Boot the PRU core & determine the associated /dev/rpmsgY instance 

The simplest way to find the association between PRU core and associated /dev/rpmsgY instance is to check the /dev/ folder before and after initializing the PRU core. The /dev/rpmsgY instance that appears after the PRU core is initialized is associated with that core.

Note that the same core might have different numbers for remoteprocX and /dev/rpmsgY.

// the existing rpmsgY instances are associated with remote cores that Linux has
// already initialized or attached to

root@am62xx-evm:~# ls /dev/
...
remoteproc0
remoteproc1
remoteproc2
remoteproc3
rfkill
rpmsg0
rpmsg1
rpmsg_ctrl0
rpmsg_ctrl1

root@am62xx-evm:~# echo start > /sys/class/remoteproc/remoteproc3/state
[  569.960588] remoteproc remoteproc3: powering up 30078000.pru
[  569.965107] remoteproc remoteproc3: Booting fw image am62x-pru1-fw, size 80152
root@am62xx-evm:~# [  569.977230] virtio_rpmsg_bus virtio2: rpmsg host is online
[  569.977263] virtio_rpmsg_bus virtio2: creating channel rpmsg-raw addr 0x1f
[  569.977292] rproc-virtio rproc-virtio.5.auto: registered virtio2 (type 7)
[  569.977302] remoteproc remoteproc3: remote processor 30078000.pru is now up

// use /dev/rpmsg2 to communicate with this PRU core
root@am62xx-evm:~# ls /dev/
...
remoteproc0
remoteproc1
remoteproc2
remoteproc3
rfkill
rpmsg0
rpmsg1
rpmsg2
rpmsg_ctrl0
rpmsg_ctrl1
rpmsg_ctrl2

We can double-check this association by searching for the rpmsgY instance under /sys/devices:

root@am62xx-evm:~# cd /sys/devices
root@am62xx-evm:/sys/devices# find -name "rpmsg2"
./platform/bus@f0000/30040000.pruss/30078000.pru/remoteproc/remoteproc3/rproc-virtio.5.auto/virtio2/virtio2.rpmsg-raw.-1.31/rpmsg/rpmsg2

// this verifies that rpmsg2 is associated with 30078000.pru & remoteproc3

Run the echo test 

root@am62xx-evm:/sys/devices# cd ~
root@am62xx-evm:~# echo "pru1 echo test" > /dev/rpmsg2
root@am62xx-evm:~# cat /dev/rpmsg2
pru1 echo test
^C