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There are many occasions when its useful to be able to talk to your mbed from a computer. This could be to control actuators using the mbeds outputs, gather data using the mbeds sensors or create remote applications over a network. Creating an interface between mbed and a computer can be difficult because it requires you to specify a communication format and then to write code on both the mbed and the computer you are interfacing with.
The mbed is capable of receving and interpretting RPC commands and this can be used to greatly simplfy creating an interface. The RPC commands are in a predefined format and can be sent over any transport mechanism that can send a stream of text. They allow you to directly interact with objects on mbed.
This page shows the code that needs to be running on mbed for RPC to work, we've also created libraries for several popular languages which allow you to use RPC over several transport mechanisms without having to have to do any work to set up the transport mechanism or formatting of your messages. Libraries have been developed for: MATLAB, LabVIEW, Python, Java and .NET.
RPC Commands are in the format: "/<Object name>/<Method name> <Arguments separated by spaces>
If you send just "/" mbed will return a list of objects that can be used
If you send "/<object name>/" then mbed will return the methods which can be used on this object.
This is an example of the RPC command required to create an LED object and turn it on:
/DigitalOut/new LED1 myled /myled/write 1
You can also interact with objects that are created in code on the mbed you just refer to them by their name.
If you want to interact with an object then make sure you define it on mbed with a name: DigitalOut myled(LED1, "myled")
On mbed you need to pass these commands into the rpc function:
char buf[256], outbuf[256]; strcpy(buf, "/DigitalOut/new LED1 myled"); rpc(buf, outbuf);
You can use any communication method to receive the string and pass it into RPC function
To carry out RPC over serial you need to receive the commands from the serial port and then pass them into the RPC function. Finally you return the result. This can be done using a program like this:
00001 #include "mbed.h" 00002 #include "rpc.h" 00003 Serial pc(USBTX, USBRX); 00004 int main() { 00005 // setup the classes that can be created dynamically 00006 Base::add_rpc_class<AnalogIn>(); 00007 Base::add_rpc_class<AnalogOut>(); 00008 Base::add_rpc_class<DigitalIn>(); 00009 Base::add_rpc_class<DigitalOut>(); 00010 Base::add_rpc_class<DigitalInOut>(); 00011 Base::add_rpc_class<PwmOut>(); 00012 Base::add_rpc_class<Timer>(); 00013 Base::add_rpc_class<SPI>(); 00014 Base::add_rpc_class<BusOut>(); 00015 Base::add_rpc_class<BusIn>(); 00016 Base::add_rpc_class<BusInOut>(); 00017 Base::add_rpc_class<Serial>(); 00018 // receive commands, and send back the responses 00019 char buf[256], outbuf[256]; 00020 while(1) { 00021 pc.gets(buf, 256); 00022 rpc(buf, outbuf); 00023 pc.printf("%s\n", outbuf); 00024 } 00025 }
Or here is a bin file which you can download straight on to your mbed: rpc_serial_lpc1768.bin Note that its not a case of either having rpc or your own code. You can do both at the same time you just need to make sure you receive the serial commands when they are sent.
Once you have this running on mbed you can control mbed from a terminal by just typing commands in the format above (make sure you have your terminal set to transmit CR+LF).
The HTTP Server has an rpc handler, so by using the HTTP server example program below and download it on to your mbed you will be able to use RPC over HTTP. The rpc commands are sent by adding them to the URL of the mbed in a browser.
RPC Commands over HTTP are in the format: http://<url of mbed>/rpc/<Object name>/<Method name> <Arguments separated by spaces>
The mbed will pass the URL it is assigned over the USB serial.
The important line of code for RPC is to add the RPC handler.
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FIR Filter 
svr.addHandler<RPCHandler>("/rpc");
A slight Alteration to Donatien's HTTP Server Example so that it registers all the classes with RPC support to demonstrate RPC over HTTP
Program published 09 Sep 2010 by 
Michael Walker
Nearly all projects involve using more than just the mbed's Digital and Analog I/O and so the RPC interface above can rapidly become insufficient and you're back to creating your own communication protocol and programming the low level communication on both the mbed and in your software application. The RPC Interface Library provides a mechanism which can help over come these problems by allowing you to call custom functions over RPC and read and write to variables on mbed using RPC. The cook book page for the RPC Interface Library gives detailed information on how to use this library within your own code.
| RPCFunction | Class to call custom functions over RPC |
| RPCVariable< T > | Class to read and set an attached variable using the RPC |
| SerialRPCInterface | Provides an Interface to mbed over RPC |
You now have a program running on mbed which handles the RPC commands. To make a complete application your software needs to set up the transport mechanism on its end and format the commands into strings. To make this easier we've created libraries that not only give you simple access to the RPC from several programming languages but also include classes for much of the mbed API. The software libraries also include classes for the RPC Interface Library to help extend RPC into your own code.
They all use a consistent interface which is a close as possible to the interface for programming on mbed. They've been designed so that is easy to switch between transport mechanisms and so that an application can control multiple mbeds.
Hi,
I am trying to use SPI with similar commands via Tera Term. When I try the command
/SPI/new myspi(p5,p6,p7) then all 4 LED's start blinking and I have to reset mbed again.
And the SPI returns "SPI pinout mappi"
Can you please put some light on the implementation of SPI constructors ? Thanks in advance.
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RPS Over Serial not working - nor is much else.. I have downloaded the bin and get no response when using PuTTY term emulator and typing commands in the format above. To check that something was working i put a pc.print("hello") line in and recompiled which worked but still no RPC functions. I am rapidly approaching end of my tether with MBED ( yes i am sure it is all my fault but TINI was so much easier and all the examples worked). Any ideas .. Many thanks.