chAT

AT command server written in C++.

Features

• Written in standard C++17
• Modern and self-explanatory APIs
• Robust and high efficiency I/O handling
• "Inhibit mode" to allow raw data transmission on same I/O medium
• The AT syntax parser can be used in standalone mode
• Rich built-in helper functions

The French word "chat" is "cat" in English.

Design principles

• Prefer usability and speed over low RAM usage
• No strict syntax checking and man-made limitations
• Does not assume anything: Max flexibility

Usage

If you're using CPM

CPMAddPackage(
        GITHUB_REPOSITORY SudoMaker/chAT
        GIT_TAG <some tag, e.g. v1.0.0 or commit id>
        GIT_SHALLOW ON
)

target_link_libraries(foo chAT)

Include & namespace

#include <chAT.hpp>
using namespace SudoMaker;

Creating a server

chAT::Server at_srv;

Knowing the types of AT command

Run

>> AT+FOO\r\n
<< OK\r\n

Read

>> AT+FOO?\r\n
<< +FOO: 123\r\n
<< OK\r\n

Write

>> AT+FOO=456\r\n
<< OK\r\n

Test

>> AT+FOO=?\r\n
<< +FOO: <number>
<< OK\r\n

Unsolicited

<< +ALARM: "Your cat ate a rat"\r\n

Be aware that they can appear at anywhere. Like:

>> AT+FOO?\r\n
<< +ALARM: "Your cat scratched your curtain"\r\n
<< +FOO: 123\r\n
<< +ALARM: "Your cat destroyed your vase"\r\n
<< +ALARM: "Your cat opened your fridge"\r\n
<< OK\r\n
<< +ALARM: "Your cat ate your salmon"\r\n

Install command handler

at_srv.set_command_callback([](chAT::Server& srv, const std::string& command) {
	auto &parser = srv.parser();        // type: chAT::ATParser&
	auto cmd_mode = parser.cmd_mode;    // type: chAT::CommandMode
	auto &argv = parser.args;           // type: std::vector<std::string>&
	auto argc = argv.size();            // type: size_t
	
	// Now assume user typed "AT+FOO=abc,123\r\n", then:
	// 'command' contains "+FOO"
	// 'cmd_mode' contains chAT::CommandMode::Write
	// 'argv' contains ["abc", "123"] (yes it starts from 0)
	// 'argc' contains 2
	
	// ... do your stuff
	
	if (success) {
		return chAT::CommandStatus::OK;       // User will see "OK\r\n"
	}
	
	if (cpu_is_on_fire) {
		return chAT::CommandStatus::ERROR;    // User will see "ERROR\r\n"
	}
	
	return chAT::CommandStatus::CUSTOM;       // No output will be produced by default
	
	// You can always add custom output via chAT::Server::write_*() functions.
});

Install I/O handlers

These functions need to return the number of bytes actually read/written. If the operation can't be completed (i.e. not a single byte has been read/written), simply return -1. However the server will not read errno. It up to the handler to handle unrecoverable errors.

at_srv.set_io_callback({
	.callback_io_read = [](auto buf, auto len){
		return read(STDIN_FILENO, buf, len);
	},
	.callback_io_write = [](auto buf, auto len){
		return write(STDOUT_FILENO, buf, len);
	},
});

If you're using non-blocking I/O (i.e. these functions return immediately), enable the nonblocking mode.

at_srv.set_nonblocking_mode(true);

Using the write helper functions

These functions can be used anywhere. But they're not thread-safe (i.e. a mutex is needed if you call them from more than 1 thread).

Server::write_data(const void *buf, size_t len);

Write data. It's simple enough.

The data is not copied and needs to be available before Server::run() completed all write tasks.

Server::write_cstr(const char *buf, ssize_t len = -1);

Write C-style string. It's basically the same as write_data, but it will comupte the string length if len is not specified.

The data is not copied and needs to be available before Server::run() completed all write tasks.

void Server::write_str(std::string str);

Write C++ std::string. std::move is used internally to save potential copies.

void Server::write_vec8(std::vector<uint8_t> vec8);

Write C++ std::vector<uint8_t>. std::move is used internally to save potential copies.

void Server::write_error();

Write ERROR\r\n.

void Server::write_error_reason(std::string str);

Write error reason. std::move is used internally to save potential copies.

Example: If str is "putain", it will write +ERROR: putain\r\n.

void Server::write_ok();

Write OK\r\n.

void Server::write_response_prompt(std::string str);

Write response. std::move is used internally to save potential copies.

Example: If the current command is +FOO and str is "bon", it will write +FOO: bon\r\n.

void Server::write_response_prompt();

Write the response prompt.

Example: If the current command is +FOO, it will write +FOO: .

void Server::write_error_prompt();

Write +ERROR: .

void Server::write_line_end();

Write \r\n.

Running the server

You only need to care about the return value in nonblocking mode.

auto rc = at_srv.run();         // type: chAT::Server::RunStatus

using RunStatus = chAT::Server::RunStatus;

if (rc & RunStatus::WantRead) {
	// Enable IN event
}

if (rc & RunStatus::WantWrite) {
	// Enable OUT event
}

Using the inhibit mode

// Assume we need to read 128 bytes of raw data from the I/O medium.

// Since the server doesn't read one byte at a time (which is slow as hell),
// some data can be already buffered by the server, so we pull them out at first.

// Inhibit server read and pull out at most 128 bytes of data from server buffer
auto raw_data = at_srv.inhibit_read(128);  // type: std::vector<uint8_t>

// Then, 'raw_data' contains 0~128 bytes of data,
// and the server won't initiate any more read operations.
// Now it's up to the user to read the remaining data from the operating system.

// After it's done, call
at_srv.continue_read();
// to continue normal operation.

// Note that the write operations are not affected.
// You can always utilize the server to arrange binary data writes.

Read buffer size limit

Currently, it's hardcoded to 1024 bytes. It's 2 times of the maximum endpoint size of USB2.0.

Write buffer size limit

The default limit is 16384 bytes. Use the following to change it:

at_srv.set_write_buffer_size_limit(1024);

When the buffer is full, the oldest data will be discarded.

If you attempt to put in a chunk of data larger than the buffer (e.g. write_vec8(large_vector)), it will cause everything in the buffer to be discarded.

Examples

See the examples directory.

• parser.cpp - Standalone AT command syntax parsing
• posix_stdio_blocking.cpp - AT command server with blocking POSIX standard I/O
• posix_stdio_nonblocking.cpp - AT command server with nonblocking POSIX standard I/O

License

AGPLv3