Re: Dynamic memory allocation?
Thanks everybody for the answers! Since I've got an upper limit for the memory that I might need, I will just use a static memory allocation of that maximum size (it's not that much anyway)... Cheers, Tobias Bluechip wrote: As someone once said to me, if you want malloc/free/etc code them. After about 10 minutes of thinking on the problem I realised just how much of my 32K of memory such algorithms would cost me and decided to write my code with static memory allocations set at compile time. Tobias, if you need any thoughts on how to live without malloc (and I really do recommend it in this case) I am happy to help here or offline. BC The (much argued over) view of the rockbox dev'ers is that dynamic memory allocation is a bad idea in embedded systems, like Rockbox. The reason usually given is that you have to deal with the 'worst case' scenario anyway (ie, all resources are needed), therefore you need at least this much ram available, in case everything is happening at once. If this is the case, you might as well statically allocate it. Oh, and its a lot simpler to not have malloc etc :) I guess if you know that 2 things are never going to need the same memory at the same time (maybe mp3 decoding and ogg decoding), why not just allocate a static buffer of mp3_or_ogg_buffer g On 1/2/06, Tobias Heimann [EMAIL PROTECTED] wrote: Hi guys, I've just started to develop a plugin for rockbox and stumbled over the memory allocation: Is there anything like malloc() and free() in rockbox and if yes, which headers do I have to include for that? So far, I've only found buffer_alloc() in buffer.h, but that results in an undefined reference error. I'm building for the coldfire m68k btw. Thanks for any help, Tobias
Re: Dynamic memory allocation?
Just curious... what kind of plugin are you trying to make? Ronald On Tue, 03 Jan 2006 12:16:55 +0100, Tobias Heimann [EMAIL PROTECTED] wrote: Thanks everybody for the answers! Since I've got an upper limit for the memory that I might need, I will just use a static memory allocation of that maximum size (it's not that much anyway)... Cheers, Tobias
Re: Dynamic memory allocation?
A conversion of the Robo Rally game (http://www.wizards.com/default.asp?x=ah/prod/roborally). I assume that this list doesn't allow attachments to show you any screenshots, but the game is coming along nicely so far... Tobias Ronald Teune wrote: Just curious... what kind of plugin are you trying to make? Ronald On Tue, 03 Jan 2006 12:16:55 +0100, Tobias Heimann [EMAIL PROTECTED] wrote: Thanks everybody for the answers! Since I've got an upper limit for the memory that I might need, I will just use a static memory allocation of that maximum size (it's not that much anyway)... Cheers, Tobias
Re: Dynamic memory allocation?
On Tue, 3 Jan 2006, Tobias Heimann wrote: I assume that this list doesn't allow attachments to show you any screenshots, but the game is coming along nicely so far... Hint: there's a wiki nearby... :-) -- Daniel Stenberg -- http://www.rockbox.org/ -- http://daniel.haxx.se/
Re: Dynamic memory allocation?
Indeed :-) http://www.rockbox.org/twiki/bin/view/Main/PluginRoboracers On Tue, 3 Jan 2006, Tobias Heimann wrote: I assume that this list doesn't allow attachments to show you any screenshots, but the game is coming along nicely so far... Hint: there's a wiki nearby... :-)
Re: Dynamic memory allocation?
Tobias Heimann wrote:
Hi guys,
I've just started to develop a plugin for rockbox and stumbled over the
memory allocation:
Is there anything like malloc() and free() in rockbox and if yes, which
headers do I have to include for that?
So far, I've only found buffer_alloc() in buffer.h, but that results in
an undefined reference error.
I'm building for the coldfire m68k btw.
Thanks for any help,
Tobias
Tobias,
Having done a fair share of commercial embedded development, I agree
with the general opinion that malloc in an embedded application is not
usually a good idea. It's not really as hard to deal with as you might
imagine though. It just requires a slightly different mindset. Once
you achieve that, it'll be a piece of cake.
Nevertheless, there are times when the best solution to a problem is to
use dynamic memory allocation. However, you often don't need the full
power of malloc/free. As some have pointed out, it's pretty easy to
allocate memory sequentially from a static buffer. The solutions shown
so far don't allow for any amount of free'ing at all however. If you do
need to use a malloc/free cycle as part of your algorithm, perhaps in a
series of nested calls or something similar, there is a fairly simple
extension of the techniques already shown that you can use. I call this
a mark/release allocator: it's basically a sequential allocator which
allocates from a static buffer but it allows you to release (free)
memory back to a previously marked level. Basically, all of the
sequential allocations since the last mark are free'd in one operation,
allowing that memory to be re-used (in a later nested call, for
example). This is a very efficient technique and, depending on what
you're doing, it can be very effective.
I've typed up the code for this from memory (pasted below). You'll
probably want to do a little testing with it first. ;)
Good luck,
~ray
--
typedef struct tagMRPOOL
{
char *base, *next;
int total, avail;
}
MRPOOL;
void mr_init(MRPOOL *pool, void *mem, int size)
{
pool-base = pool-next = mem;
pool-total = pool-avail = size;
}
int mr_mark(MRPOOL *pool)
{
return (int) pool-next - pool-base;
}
void * mr_alloc(MRPOOL *pool, int size)
{
void *mem = NULL;
if (size = pool-avail)
{
mem = pool-next;
pool-next += size;
pool-avail -= size;
}
return mem;
}
void mr_release(MRPOOL *pool, int mark)
{
assert( (mark = 0) (mark pool-total) );
pool-next = pool-base + mark;
pool-avail = pool-total - mark;
}
// useful for temporary string copies:
char *mr_strdup(MRPOOL *pool, const char *str)
{
int size = strlen(str) + 1;
char *newstr = mr_alloc(pool, size);
if (newstr)
strcpy(newstr, str);
return newstr;
}
--
Here's a usage example:
extern char static_buffer[];
static MRPOOL pool;
void myalgo()
{
mr_init(pool, static_buffer, sizeof(static_buffer)); // always init
first!
char *somemem = mr_alloc(pool, size_needed);
while( some_nested_op() );
// no need to release when top level exits
}
bool some_nested_op()
{
int mark = mr_mark(pool); // always mark (once) before alloc
char *somemem = mr_alloc(pool, size_needed);
char *moremem = mr_alloc(pool, size_needed2);
while( another_nested_op() );
mr_release(pool, mark); // always release before exit (if did alloc)
return false;
}
bool another_nested_op()
{
int mark = mr_mark(pool);
char *somemem = mr_alloc(pool, size_needed);
char *moremem = mr_alloc(pool, size_needed2);
mr_release(pool, mark);
return false;
}
--
Note: It's even possible to return dynamic memory from a subroutine so
long as the subroutine doesn't release it before exit. If the
subroutine must release, and the size of the memory to be returned is
known in advance, it can pre-allocate the return buffer before it
'marks'. (Alternately, the caller can allocate the return buffer and
pass it in.)
Hope this is helpful!
Re: Dynamic memory allocation?
AWESOME - probably my favourite board game of all time. BC At 22:58 03/01/2006, you wrote: A conversion of the Robo Rally game (http://www.wizards.com/default.asp?x=ah/prod/roborally). I assume that this list doesn't allow attachments to show you any screenshots, but the game is coming along nicely so far... Tobias Ronald Teune wrote: Just curious... what kind of plugin are you trying to make? Ronald On Tue, 03 Jan 2006 12:16:55 +0100, Tobias Heimann [EMAIL PROTECTED] wrote: Thanks everybody for the answers! Since I've got an upper limit for the memory that I might need, I will just use a static memory allocation of that maximum size (it's not that much anyway)... Cheers, Tobias
