![]() ![]() If you are not certain about dynamic allocation, use std libs (e.g.: std:vector, std::string), or smart pointers. This forces you to think about the size of the array, and its scope (lifetime), so that it gets released when it’s no longer needed. This is particularly true if you intend to, e.g.: embed html strings.ĭon’t use global static arrays, such as uint8_t buffer. Some techniques for reducing memory usageĭon’t use const char * with literals. Now is time to re-read about the exception decoder. Instrumenting the code with the OOM debug option and calls toĮSP.getFreeHeap() / ESP.getHeapFragmentation() /ĮSP.getMaxFreeBlockSize() will help the process of finding memory issues. Rely on exceptions for error handling, which is not available for the ESP, and in anyĬase there is no access to the underlying code. For example, std::vector is available for use. On the other hand, some libraries don’t have the allocation code accessible for ![]() For example, the String object methods don’t allow for error handlingĪt the user application level (i.e.: no old-school error returns). So why do these silent failures exist? On the one hand, there are specific interfaces that With the requested size, even though the sum of all holes is greater than the requested Many such operations, it can happen that all available holes are too small to comply A sequence of String concatenations causes manyĪllocations/deallocations/reallocations, which makes “holes” in the memory map. The reason for theįailure is that an allocation requires finding a single free memory block that is largeĮnough for the size being requested. Silently fail even though there is enough total heap available. Multiple times, will cause memory fragmentation. In addition, doing many String concatenations in sequence, e.g.: using operator+() IfĪllocation has failed internally, then the internal string copy can corrupt data, and A typical example is when setting or concatenating a large String. The ESP leaves out exceptions (they use memory), memory allocations that fail will do Running out of heap is the most common cause for crashes. Longer it is away from servicing the WiFi stack, the more likely that memory corruption In general, the CPU must not be hogged by the user code, as the The hard timing requirements depend on the WiFi configuration andĪmount of traffic. Timing is not as tight as an ISR, but it should remain below a few milliseconds. It is not possible to execute delay() or yield() from an asynchronous callback. Than ISRs, but some restrictions still apply. Asynchronous CallbacksĪsynchronous CBs, such as for the Ticker or ESPAsync* libs, have looser restrictions It isĬonsidered best practice to set a flag within the ISR, and then from within the loop()Ĭheck and clear that flag, and execute code. ![]() That executed code should not take longer than a very few microseconds. Or do blocking operations, or operations that disable the interrupts, e.g.: readįinally, an ISR has very high restrictions on timing for the executed code, meaning In addition, it is not possible to execute delay() or yield() from an ISR, Not only that, but the entire function treeĬalled from the ISR must also have the IRAM_ATTR declared.īe aware that every function that has this attribute reduces available memory. That means that, if you use a hardware ISR, such asĪttachInterrupt(gpio, myISR, CHANGE) for a GPIO change, the ISR must have the However, the cache currently can’t be usedĭuring hardware interrupts. Other Causes for Crashes ¶ Interrupt Service Routinesīy default, all functions are compiled into flash, which means that theĬache may kick in for that code. ![]()
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