Overview
========
The Multicore RPMsg-Lite string echo project is a simple demonstration program that uses the
MCUXpresso SDK software and the RPMsg-Lite library and shows how to implement the inter-core
communicaton between cores of the multicore system.

It works with Linux RPMsg master peer to transfer string content back and forth. The name service
handshake is performed first to create the communication channels. Next, Linux OS waits for user
input to the RPMsg virtual tty. Anything which is received is sent to M4. M4 displays what is
received, and echoes back the same message as an acknowledgement. The tty reader on the Linux side
can get the message, and start another transaction. The demo demonstrates RPMsg’s ability to send
arbitrary content back and forth. Note: The maximum message length supported by RPMsg is now 496
bytes. String longer than 496 will be divided by virtual tty into several messages.

Shared memory usage
This multicore example uses the shared memory for data exchange. The shared memory region is
defined and the size can be adjustable in the linker file. The shared memory region start address
and the size have to be defined in linker file for each core equally. The shared memory start
address is then exported from the linker to the application.

Toolchain supported
===================
- GCC ARM Embedded  9.2.1
- IAR embedded Workbench  8.50.1

Hardware requirements
=====================
- Micro USB cable
- MIMX8MQ6-EVK  board
- J-Link Debug Probe
- 12V power supply
- Personal Computer

Board settings
==============
No special is needed.


Prepare the Demo
================
1.  Connect 12V power supply and J-Link Debug Probe to the board, switch SW701 to power on the board
2.  Connect a USB cable between the host PC and the J1701 USB port on the target board.
3.  Open two serial terminals for A53 core and M4 core with the following settings:
    - 115200 baud rate
    - 8 data bits
    - No parity
    - One stop bit
    - No flow control
4.  Using U-Boot command to run the demo.bin file. For details, please refer to Getting Started with MCUXpresso SDK i.MX 8M Quad.pdf
5.  After running the demo.bin, using the "boot" command to boot the kernel on the A core terminal;
6.  After the kernel is boot, using "root" to login.
7.  After login, make sure imx_rpmsg_tty kernel module is inserted (lsmod) or insert it (modprobe imx_rpmsg_tty).

Running the demo
================
After the boot process succeeds, the ARM Cortex-M4 terminal displays the following information:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
RPMSG String Echo FreeRTOS RTOS API Demo...

Nameservice sent, ready for incoming messages...
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
After the Linux RPMsg tty module was installed, the ARM Cortex-M4 terminal displays the following
information:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Get Messgae From Master Side : "hello world!" [len : 12]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The user can then input an arbitrary string to the virtual RPMsg tty using the following echo command on
Cortex-A terminal:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
echo test > /dev/ttyRPMSG30 log below shows the output of the RPMsg-Lite str echo demo in the terminal window:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
On the M4 terminal, the received string content and its length is output, as shown in the log.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Get Message From Master Side : "test" [len : 4]
Get New Line From Master Side
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Customization options
=====================