UPRINT Facility For AVR Logging in C++

Functions like sprintf() are monolithic and large. They also mean having to guess at creating potentially large buffer sizes--which are frequently overestimated. So embedded code wishing to be thrifty tends to manually make individual calls to uart_puts() interspersed with calls to atoi() on tiny reused buffers.

This logging utility offers a better notation for the same goal. It uses variadic parameters to run uart_puts() from left to right on its arguments without creating a buffer for the entire line:

uprint("Value:", 10);                         // => `Value: 10\n`
uprint("Values:", 10, 20);                    // => `Values: 10 20\n`

A newline is added at the end automatically. Spacing between items is also added by default, but instructions can be used to suppress it.

uprint("Value:", nospace, 10);                // => `Value:10\n`
uprint("[", unspaced(304), "]");              // => `[304]\n`
uprint("Foo", comma, "Bar");                  // => `Foo, Bar\n`

To make new types printable via uprint, declare an overload of the function uprint_helper(). Here's an example for a typical coordinate point class:

namespace Uprint {  // put helpers into the Uprint namespace
    inline void uprint_helper(const Point &pt) {
        uart_putc('(');
        uprint_helper(pt.x);  // can reuse existing helpers (e.g. int)
        uart_putc(',');
        uprint_helper(pt.y);
        uart_putc(')');
    }
}  // end namespace Uprint

For common formatting needs, utility class generators are provided which are the same size as the fundamental type they wrap:

uprint("Value:", Uprint::hex(10));            // => `Value: D\n`
uprint("Value:", Uprint::binary(4));          // => `Value: 100\n`
uprint("Current:", Uprint::units(5, "mA"));   // => `Current: 5mA\n`

(Note: See remarks on Uprint::Hex regarding printing of leading zeros.)

Mocking

Sometimes embedded codebases are factored in such a way that parts of them can be built for desktop machines like x86. uprint() is being designed with an eye toward working in such an environment.

As a first step, you can build and test this with plain GCC (non-AVR):

 $ g++ -DMOCKING=1 uart_logger.cpp -o test
 $ ./test

hostilefork/uart-logger

UPRINT Facility For AVR Logging in C++

Mocking