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| # Hints for quicker & better RIOT development {#dev-best-practices} | ||
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| [TOC] | ||
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| * Use the [methodology](#methodology) described below. | ||
| * Use [`ccache`](@ref ccache) to speedup compilation | ||
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| ## Coding "Dos" and "Don'ts": {#coding-dos-and-donts} | ||
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| ### Dos | ||
| * Use static memory. See also [Static vs. Dynamic Memory](#static-vs-dynamic). | ||
| * Select the priorities carefully. | ||
| * Minimize stack usage with `DEVELHELP` and `CREATE_STACKTEST`. | ||
| * Use threads to increase flexibility, modularity, and robustness by leveraging IPC. | ||
| * Use unsigned or signed integer (`unsigned`, `int`, `size_t` or `ssize_t`) for loop variables wherever possible, but keep in mind that on some platforms an `int` has a width of only 16-bit. In general, you should avoid types like `uint8_t` for loop iterators as they will probably make it more expensive on some platforms. | ||
| * Join and factor out parts of the code with existing code in RIOT, where it makes sense. | ||
| * Check all `size/length` parameters when passing memory, e.g. using `sizeof(x)` or `strlen(x)` as appropriate. Make sure you don't use the wrong one with a pointer. | ||
| * Make sure all code paths can be reached. Make sure there are no always `true/false` conditions. | ||
| * Make sure all critical sections (`lock/unlock`, `acquire/release`, ...) are always closed on every code path. | ||
| * Make sure return values are consistent with our API documentation. | ||
| * Use `assert()` statements to check parameters rather than returning an error code at run-time, to keep the code size down. | ||
| * Use the `DEBUG(...)` macro rather than `log_x(...)` | ||
| * Declare all internal module variables and functions `static` | ||
| * Make sure variables are reduced in scope as much as possible | ||
| * Use an appropriate signedness in your variables | ||
| * Make sure the variables are big enough to prevent overflow. Be aware that the code may run on platforms with different sizes of variables. For example, `int/unsigned` is only 16-bit on msp430 and avr8. If in doubt, use portable types. | ||
| * Reduce the number of function calls as far as possible without duplicating code. | ||
| * Use good judgement when using `static inline` functions and macros. If they are used in multiple places, is the increase in performance worth the penalty in code size? | ||
| * Use memory judiciously in general. For example: | ||
| ```c | ||
| typedef enum { | ||
| A, | ||
| B, | ||
| ... | ||
| } foo_t; | ||
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| int bar(foo_t v) | ||
| { | ||
| int abc; | ||
| ... | ||
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| switch(v) { | ||
| case A: | ||
| abc = 23; | ||
| break; | ||
| case B: | ||
| abc = 42; | ||
| break; | ||
| ... | ||
| } | ||
| ... | ||
| } | ||
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| /* VS */ | ||
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| typedef enum { | ||
| A = 23, | ||
| B = 42, | ||
| ... | ||
| } foo_t; | ||
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| int bar(foo_t v) { | ||
| int abc = v; | ||
| ... | ||
| } | ||
| ``` | ||
| ### Don'ts | ||
| * Don't use too many threads. Try not to use more than one thread per module. Don't create threads for one-time tasks. | ||
| * Don't use the POSIX wrapper if implementing something from scratch. | ||
| * Don't allocate big chunks of memory (for instance the IPC message queue) on the stack, but use rather static memory for that. | ||
| * Don't over-provision memory. | ||
| * Don't pass stack memory between different contexts unless you can prove conclusively that it won't be a problem. | ||
| * Don't use enums for flags, because flags have a width in memory that is in most cases smaller than `sizeof(enum)` (most bitfields are 16 bits max, on most of our newer platforms, `sizeof(enum)` is however 32 bits). This results in every assignment needed to be cast to either `uint8_t` or `uint16_t`. With macros you don't need to cast since they are typeless. Making the enum packed makes its width unpredictable in terms of alignment issues, when used in struct. | ||
| * Don't duplicate code from elsewhere in the RIOT code base, unless there is a very good reason to do so. | ||
| * Don't duplicate code within your own code, unless there is a very good reason to do so. Use internal functions to this end. | ||
| * Don't mix up logical and bitwise operations (`!` vs `~`, or `&&` vs `&`) | ||
| ## Methodology: emulator first, target IoT hardware last! {#methodology} | ||
| The below methodology is recommended, using well-known de facto standard tools from the FLOSS community that are compatible with RIOT. Using the below workflow improves time-to-running-code compared to typical IoT software workflows (which can be as retro as "LED-driven" debugging). | ||
| 0. For newbies, preliminaries are typically faster with the provisioned virtual environment setup, e.g. with **Vagrant**. | ||
| 1. To check your code, first use available **static analysis** as much as possible initially, which means (i) enable all compiler warnings and fix all problems found, then (ii) use a supported linter such as **cppcheck** to find bad coding patterns (i.e. code smells) and identify misuse of standard APIs. | ||
| 2. Next, use available **dynamic analysis** tools to find further defects while running the code on **RIOT native**, which means (i) running unit tests and integration tests on RIOT native emulator, and (ii) using **Valgrind** memcheck, as well as the **GCC stack smashing detection**, to detect and avoid undefined behavior due to invalid memory access. | ||
| 3. In case of networked applications or protocols, test **several instances of native** communicating via a virtual network mimicking the targeted scenario, which means (i) either using the default virtual full-mesh or other topologies configured via DESvirt, and (ii) using **Wireshark** to capture and analyze virtual network traffic, e.g. to ensure protocol packets are syntactically correct, and to observe network communication patterns. | ||
| 4. In case of incorrect behavior at this stage, analyze the system state for semantic errors on native using the standard debugger **gdb**, which allows virtually unlimited conditional breakpoints, record and replay, catchpoints, tracepoints and watchpoints. | ||
| 5. In case of suspected performance bottleneck, use performance profilers **gprof**, or else cachegrind, to identify precisely the bottlenecks. | ||
| 6. At this stage the implementation has proven bug-free on the native emulator. One can thus finally move on to hardware-in-the-loop, which means (i) flashing the binary on the targeted IoT hardware, typically using standard flasher **OpenOCD** or **edbg**, and (ii) using the **RIOT shell** running on the target IoT device(s) for easier debugging on the target hardware. | ||
| 7. In case the hardware is not available on-site, one can consider remotely flashing and testing the binary on supported open-access testbeds, e.g. [IoT-LAB](https://www.iot-lab.info) hardware is fully supported by RIOT. | ||
| 8. In case of failure, after analyzing the failure and attempting to fix the defect, go back to step 1 to make sure the fix did not itself introduce a new defect. | ||
| ## Static vs. Dynamic Memory {#static-vs-dynamic} | ||
| In your C program you have to decide where the memory you want to use comes from. | ||
| There are two ways to get memory in your C code: | ||
| 1. Define static memory. | ||
| 2. Use dynamic memory (call `malloc()`/`free()` to get memory from the heap). | ||
| Both ways have some drawbacks which are listed here. | ||
| If you want to analyze the static memory consumption of your code you can use [otm](https://github.com/LudwigOrtmann/otm) or `make cosy`. | ||
| ### Static memory | ||
| * Access the memory in one operation O(1) ⇒ real time condition | ||
| * Programmer needs to know the amount of memory on compile time | ||
| * Leads to over and undersized buffers | ||
| * Forces the programmer to think about the amount of need memory at compile time | ||
| ### Dynamic memory | ||
| * `malloc()` and `free()` are implemented in your `libc` (RIOT on ARM: `newlib`/`picolib`) | ||
| * Runtime behavior is not predictable | ||
| * Code can request the amount of memory it needs on runtime | ||
| * On most platforms: the size of the heap is `sizeof(<RAM>)-sizeof(<static memory>)` | ||
| * If you reduce your usage of static memory your heap gets bigger | ||
| * On some platforms calling `free()` will not or not always make heap memory available again (see @ref oneway_malloc on MSP430) | ||
| * Programmer needs to handle failed memory allocation calls at runtime | ||
| * Static code analysis is unable to find errors regarding memory management |
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