Embedded Planet
Examples for the mbed-rpc library
ep-oc-example-mbed-rpc
Examples for the mbed-rpc library
This repository contains examples of using the mbed-rpc library with Mbed-OS. See each subdirectory for directions on building the examples
Building Examples - General
Generally, the examples just need to be initialized and all dependencies pulled in. The examples use Mbed’s CLI tools for this.
You will need to install mbed-cli and associated tools before building these examples.
Once mbed-cli is installed, simply navigate to the example’s directory, follow the directions in that example’s specific README for generating any additional sources, and then execute the following:
mbed new .
mbed deploy
This will pull in all dependencies automatically. Make sure to set up your target and toolchain before executing mbed compile.
Configuration and Memory Optimization
While erpc is very lightweight already, hosting an erpc server and acting as an erpc client currently requires pulling in Mbed’s RTOS libraries.
This can make it impossible to run on more constrained targets – especially in terms of RAM consumption.
It is possible to reduce static RAM usage by changing the configuration using Mbed’s JSON-based build configuration system.
Some settings that can decrease RAM usage:
Memory Optimization – Decrease Main Thread Stack Size
Depending on your application’s RAM requirements, you can reduce the default size of the main thread stack. An example mbed_app.json file accomplishing this is shown below:
{
"target_overrides": {
"*": {
"rtos.main-thread-stack-size": 1024,
}
}
}
By default, the main thread stack size is set to 4kB! Changing this can cut RAM usage significantly if your application isn’t doing much other than RPC calls and lightweight processing. Make sure not to decrease the stack size too much or you’ll encounter stack overflow errors.
Memory Optimization – Decrease Default Thread Stack Size
Similar to above, any additional threads created at runtime are given a default stack size of 4kB! You can either change this in code (by passing a non-zero size parameter to the Thread object’s constructor) or change the default stack size allocated to new threads.
To do this, add the following line to your mbed_app.json configuration file:
"rtos.thread-stack-size": 1024
Memory Optimization – Adjusting Buffer Sizes
If you are using the UARTTransport class included in mbed-rpc you should note that it is a buffered UART implementation. Due to the design of erpc, this is required to ensure incoming messages are received completely.
By default, the RX and TX buffers are 256 bytes each in size. You can adjust this by adding the following lines to your mbed_app.json file:
"drivers.uart-serial-txbuf-size": 128,
"drivers.uart-serial-rxbuf-size": 128
Additionally, erpc allocates buffers messages internally with a default size of 256 bytes each. You can change the default buffer size allocated by erpc by each MessageBufferFactory by adding the following line to your mbed_app.json:
"mbed-rpc.erpc-default-buffer-size": 128
Flash/RAM Usage Optimization – Release Build Profile
Mbed’s build system uses profiles to adjust optimization and compiler flags. The most optimized build profile included with Mbed is the release profile. It can sometimes shave off a few extra kB of flash/RAM usage.
To build using the release profile, add the --profile flag to your mbed compile command as shown below:
mbed compile --profile ./mbed-os/tools/profiles/release.json
Real-World Results
With all the above optimizations taken into account, the SimultaneousClientServer demo application was able to successfully run on an STM32L073RZ Nucleo board (128kB flash / 20kB RAM)
Note that even with the debug configuration it is possible to run SimultaneousClientServer on this target but it uses a majority of the RAM (~15kB).
In entirety, the mbed_app.json used for this build is shown below:
{
"target_overrides": {
"NUCLEO_L073RZ": {
"rtos.main-thread-stack-size": 1024,
"rtos.thread-stack-size": 1024,
"drivers.uart-serial-txbuf-size": 128,
"drivers.uart-serial-rxbuf-size": 128,
"mbed-rpc.erpc-default-buffer-size": 128
}
}
}
and the build command was mbed compile --profile ./mbed-os/tools/profiles/release.json.
The build output is shown below, with a reduced Flash/RAM footprint of ~65kB/8.7kB:
Building project SimultaneousClientServer (NUCLEO_L073RZ, GCC_ARM)
Scan: SimultaneousClientServer
Link: SimultaneousClientServer
Elf2Bin: SimultaneousClientServer
| Module | .text | .data | .bss |
|----------------------------------|-----------|----------|----------|
| [fill] | 100(+0) | 8(+0) | 23(+0) |
| [lib]/c.a | 17260(+0) | 2472(+0) | 89(+0) |
| [lib]/gcc.a | 8568(+0) | 0(+0) | 0(+0) |
| [lib]/misc | 216(+0) | 4(+0) | 28(+0) |
| [lib]/stdc++.a | 0(+0) | 0(+0) | 0(+0) |
| ep-oc-mcu/devices | 56(+0) | 0(+0) | 36(+0) |
| erpc-files/blink_led_server.o | 214(+0) | 0(+0) | 0(+0) |
| erpc-files/button_input_client.o | 112(+0) | 0(+0) | 0(+0) |
| main.o | 2752(+0) | 20(+0) | 1136(+0) |
| mbed-os/components | 36(+0) | 0(+0) | 0(+0) |
| mbed-os/drivers | 3440(+0) | 0(+0) | 0(+0) |
| mbed-os/events | 1308(+0) | 0(+0) | 0(+0) |
| mbed-os/hal | 1610(+0) | 8(+0) | 130(+0) |
| mbed-os/platform | 3554(+0) | 260(+0) | 284(+0) |
| mbed-os/rtos | 9912(+0) | 168(+0) | 3164(+0) |
| mbed-os/targets | 9832(+0) | 4(+0) | 806(+0) |
| mbed-rpc/erpc | 2970(+0) | 0(+0) | 0(+0) |
| Subtotals | 61940(+0) | 2944(+0) | 5696(+0) |
Total Static RAM memory (data + bss): 8640(+0) bytes
Total Flash memory (text + data): 64884(+0) bytes
Image: ./BUILD/NUCLEO_L073RZ/GCC_ARM-RELEASE/SimultaneousClientServer.bin