by jar » Fri Apr 15, 2016 5:20 am
They're modeled after the .
The 32KB of memory in an Epiphany-III core looks something like this:
When you use brk/sbrk, you are manipulating the free space heap. You can think of it a bit like a malloc, but there is no memory virtualization. The pointer that is returned is a physical address rather than a virtual address that a malloc may give you.
The first call void* memfree = coprthr_tls_sbrk(0) returns the pointer to the beginning of the free space. The internal pointer that keeps track of the boundary of free space is incremented by 0, and the original value is returned. When you give a size N to sbrk(N), you are getting the current pointer value of free space and the internal value is incremented by N. Finally, when you call brk(memfree), you are resetting the internal free space pointer back to the original value that it had when you first called sbrk(0).
It's very simple. There isn't much happening inside the routines. They are lower level than a malloc. You can't malloc space on the cores like you traditionally would on the host.
If you don't intend to release memory before ending your program, you do not need the initial sbrk(0) or the final brk(memfree). It will still work, but is poor practice like not freeing malloc'd memory.
If you want to know more about what's coming down the pike, read these two pre-print manuscripts below. They were just uploaded in the last few hours.
