aTalk is an implementation of a real time data link layer communication protocol based on the exchange of ASCII encoded messages. This design has two main pourposes. The first is to keep the maximum compatibility with comunication channels that do not tolerate well binary data, i.e. serial interfaces. The second is to allow an easy inspection the content of the messages for monitoring, debugging, etc.
Here is an example of an aTalk message with a payload of 11 bytes of binary data. aTalk messages are surrounded by brackets that mark the start and the end of each message. The two following character strings represent the message coded in hexadecimal ASCII (base 16) and coded in base 64 ASCII respectively.
{1110ff6c963715ffa4ce92dcabbaff7514}
{EQH/xmlzUf9K7CnNuqv/V0E=}
When the consumption of communication bandwidth is critital, the base 64 encoding is the better choice, it has only 33% of band overhead against the original binary data. Otherwise, the hexadecimal encoding is more useful for debug or monitoring pourposes, since it is far more human readable than the base 64 encoding.
- real time oriented communication protocol.
- no message handshake.
- messages base 16 or base 64 ASCII encoded.
- data payload from 0 to 255 bytes.
- data link error detection.
- lost message detection.
- C language lightweight implementation.
- hardware data link drivers API.
- drivers for serial interface and local software loop included.
- supported platforms: Linux and Arduino.
- tested on PC (cpu 64bit), arduino nano (cpu AVR328), NodeMCU (cpu ESP8266), NodeMCU 32s (cpu ESP32), CORE-ESP32 (cpu RISC-V).
The package is splitted in several git repositories. One repository with an aTalk library for each supported platform and one repository for the aTalk core files common to all platforms. These are source libraries to be compiled togheter with the application software. The repositories names are:
* aTalk the aTalk core common files * aTalkArduino the aTalk library for Arduino * aTalkLinux the aTalk library for Linux
Also the following examples using the aTalk libraries are provided.
- single host local communication loop
- dual host remote communication loop
To begin with aTalk programming, the Linux-Arduino communication example is a good starting point.
For installation details see the example above.
struct aTalk* atalk_init( uint8_t data_size_max, enum aTalkEncoder encoder)
Called once by the application before to start the aTalk communication, wich means before to call atalk_send or atalk_receive. It allocates the required data structures and it inits all required variables.
data_size_max: the maximum size (number of bytes) of binary data to be exchanged by aTalk messages.
encoder: the requested message encoding, BASE16 or BASE64.
return data: a pointer to the control structure of aTalk. If pointer is NULL atalk_init failed.
int atalk_send( struct aTalk* atalk, uint8_t* data, uint8_t data_size)
Called by the application each time it is needed to send a buffer of binary data by an aTalk message.
atalk: a pointer to the control structure of aTalk.
data: a pointer to the binary data buffer to be sent with an aTalk message.
data_size: the size of the binary data buffer to be sent.
return data: error code, =0 function successful, <0 error happened.
int atalk_receive( struct aTalk* atalk, uint8_t* data, uint8_t* data_size)
Called by he application to receive an aTalk message. The function terminates when an aTalk message is received or when no message is received whitin a given time out interval (see data link driver).
atalk: a pointer to the control structure of aTalk.
data: a pointer to the binary data buffer where to write the binary data received by an aTalk message.
data_size: the size of the received binary data.
return data: error code, =0 function successful, <0 error happened.
Send wishes, comments, patches, etc. to mxgbot_a_t_gmail.com .
aTalk internals can be found at Developer information .
aTalk is authored by Fabrizio Pollastri <mxgbot_a_t_gmail.com>, year 2019, under the GNU Lesser General Public License version 3.