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Hello, I am using Keil uVision3 V3.55 for Si-labs C8051F02X series. I am using "init_mempool" function, so that I can use the functions like "malloc", "free", etc. Here is my source code --
#include<c8051f020.h> #include<stdlib.h> void main(void) { unsigned char xdata *ptr, *ptr1; init_mempool(0x05,15); ptr = malloc(10); ptr1 = malloc(5); *ptr++ = 11; *ptr++ = 22; *ptr++ = 33; *ptr++ = 44; *ptr1++ = 1; *ptr1++ = 2; *ptr1++ = 3; }
I am expecting that, all the above data to be put from the locations 0x05(in xdata) onwards. But, I found that "ptr1" points to 0x00(in xdata), and "ptr" points to 0x09(in xdata). So, what is the role of "init_mempool" function here? Why does "malloc" allocate memory from 0x00??
Thanks in advance,
Regards, Heramb Phadke
Not sure - it is quite uncommon for the RTL manuals to mention the overhead inside a heap manager.
A heap is something you normally use when you don't have to care about a minimum number of concurrent allocations - either because you have an almost infinite amount of memory, or because you can either let the program die or just fail a specific operation in case of an allocation failure.
The compiler vendors are free to change the implementation whenever they like, so any code that can't see the heap implementation as a black box should stay away from it in the first place.
In this particular case, the source is provided:
http://www.keil.com/support/man/docs/c51/c51_ap_memalloc.htm
Seems to be a quite traditional design. A bit of header information always consumed with at least a free list, and then each allocated block gets extended with a pointer and a size.
Nowhere near supporting 15 bytes of allocation from a 15 byte large heap, i.e. assuming that the heap has zero overhead.