embedded

Can someone explain the mechanics of a jump table and why is would be needed in embedded systems? A jump table can be either an array of pointers to functions or an array of machine code jump instructions. If you have a relatively static set of functions (such as system calls or virtual functions for a class) then you can create this table once and call the functions using a simple index into the array. This would mean retrieving the pointer and calling a function or jumping to the machine code depending on the type of table used. The benefits of doing this in embedded programming are: Indexes

Very often malloc() is absolutely not allowed when programming for embedded systems. Most of the time I'm pretty able to deal with this, but one thing irritates me: it keeps me from using so called 'opaque types' to enable data hiding. Normally I'd do something like this: // In file module.h typedef struct handle_t handle_t; handle_t *create_handle(); void operation_on_handle(handle_t *handle, int an_argument); void another_operation_on_handle(handle_t *handle, char etcetera); void close_handle(handle_t *handle); // In file module.c struct handle_t { int foo; void *something; int another

I read somewhere once that the modulus operator is inefficient on small embedded devices like 8 bit micro-controllers that do not have integer division instruction. Perhaps someone can confirm this but I thought the difference is 5-10 time slower than with an integer division operation. Is there another way to do this other than keeping a counter variable and manually overflowing to 0 at the mod point? const int FIZZ = 6; for(int x = 0; x < MAXCOUNT; x++) { if(!(x % FIZZ)) print("Fizz\n"); // slow on some systems } vs: The way I am currently doing it: const int FIZZ = 6; int fizzcount = 1; for

When is it appropriate to use CRC for error detection versus more modern hashing functions such as MD5 or SHA1? Is the former easier to implement on embedded hardware? CRC works fine for detecting random errors in data that might occur, for example, from network interference, line noise, distortion, etc. CRC is computationally much less complex than MD5 or SHA1. Using a hash function like MD5 is probably overkill for random error detection. However, using CRC for any kind of security check would be much less secure than a more complex hashing function such as MD5. And yes, CRC is much easier