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Readme.md

To see the assembly output:

add arm-none-eabi-objdump -D "${BuildArtifactFileBaseName}.elf" > "${BuildArtifactFileBaseName}.lst" to Project > Properties > C/C++ Build > Settings > Build Steps (tab) > Post-build steps. Source

It is recommended to set optimization in Release builds to -O3 rather than the default -Osize. Change this in Project > Properties > C/C++ Build > Settings > Tool Settings (tab) > MCU GCC Compiler > Optimization > Optimization Level. You may need to click in and out of Settings to get the right tab to show.

Turn off auto breakpoint on main

By default, when you debug a project, STM Cube will pause execution before starting main(). To disable this, go to Run > Debug Configurations... then Startup and uncheck "Set breakpoint at: main". Disabling main breakpoint

Recommended Compiler Warnings

I recommend turning these on in every project you make. Go to Project > Properties > C/C++ Build > Settings > MCU GCC Compiler > Miscllaneous. Don't forget to add them for Debug and Release.

  • -Wshadow - Warns if you declare a variable with the same name as a global variable.
  • -Winline - Warns if a function specified as inline can't be inlined.
  • -Wvla - Warns if a variable length array (vla) is written.
  • -Wstrict-prototypes - This requires complete prototypes / forward declarations of functions. In C, a function declaration like void func() is actaully a function that can take any number of arguments, not no arguments. For a no argument function, write void func(void).
  • -Wlogical-op - Warns if an express is redundant in a logical operation.
  • -Wshift-negative-value - Warns when left shifting a negative value, which can interfere with the sign bit.
  • -Wtype-limits - Warns if a comparison to a type is always true or always false.
  • -Wmissing-parameter-type - Warns if you don't write a parameter type (ex: int func(arg)) which defaults to int.
  • -Wmissing-prototypes - Warns if you don't have a prototype for a function ahead of it's definition.
  • -Wmissing-field-initializers - Warns if you initialize a struct and omit initializing a field, possibly because it was forgotten.
  • -Wimplicit-fallthrough=2 - Warns if a case statement in a switch does not have break before the following case. Writing "fallthrough" or variations (see GCC warnings page) signals that the omission is intentional and no warning is emitted.
  • -Wcast-qual - Warns if you cast away const-ness of a variable/expression.
  • -Wignored-qualifiers - Warns if there's a qualifier in a function return type (const usually) that does nothing. Possibly misplaced and hiding a bug.
  • -Wpointer-arith - Warns if you take the sizeof function or void. Bad practice and hopefully unintentional.
  • -Wunsafe-loop-optimizations - Warns if loop optimizations can't be done because the loop condition is weird.
  • -Wduplicated-branches - Warns if two branches in an if statement do the same thing.
  • -Wduplicated-cond - Warns if two conditions in an if-elseif chain have the same condition.

The below warnings will produce many warnings in the STM generated code, but I recommend you add them to any file you write.

  • #pragma GCC diagnostic warning "-Wunused-macros" - Warns if a macro is not used.
  • #pragma GCC diagnostic warning "-Wunused-parameter" - Warns if a function parameter is not used.
  • #pragma GCC diagnostic warning "-Wsign-compare" - Warns about comparing a signed to an unsigned value.
  • #pragma GCC diagnostic warning "-Wconversion" - Warns about implicit conversions between types.
  • #pragma GCC diagnostic warning "-Wredundant-decls" - Warns about a variable that is redeclared.
  • #pragma GCC diagnostic warning "-Wswitch-default" - Warns if a switch has no default case.
  • #pragma GCC diagnostic warning "-Wswitch-enum" - Warns if the expression in the switch is an enum and one enum constant is missing a case.

Enabling strict prototypes and missing prototypes will cause warnings in syscalls.c. Replace errno with the following code and insert the missing void to fix these warnings.

#pragma GCC diagnostic ignored "-Wmissing-prototypes"
#pragma GCC diagnostic ignored "-Wstrict-prototypes"
extern int errno;
#pragma GCC diagnostic warning "-Wstrict-prototypes"

And add void *_sbrk(ptrdiff_t inc); to line 32 in sysmem.c.

References:

Useful macros:

Compiler time (aka static) assert

#define ASSERT_CONCAT_(a, b) a##b
#define ASSERT_CONCAT(a, b) ASSERT_CONCAT_(a, b)
#define compile_assert(e) enum { ASSERT_CONCAT(assert_line_, __LINE__) = 1/(!!(e)) }
// From: http://www.pixelbeat.org/programming/gcc/static_assert.html

Usage:

compile_assert(sizeof(my_struct_t) == 4);

Number of elements in an array

#define N_ELEMENTS(ARR) (sizeof(ARR) / sizeof(ARR[0]))

Usage

for(uint32_t i = 0; i < N_ELEMENTS(buffer); ++i) {

Mask of lowest n bits

#define MASK_OF(N_BITS) (((N_BITS) << 1) - 1)

Usage

uint8_t lowestByte = data & MASK_OF(8);  // Macro will return 0xFF