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Retrofitted comments from GEOS overlay demo to regular overlay demo.

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git-svn-id: svn://svn.cc65.org/cc65/trunk@5789 b7a2c559-68d2-44c3-8de9-860c34a00d81
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ol.sc 2012-07-19 12:25:04 +00:00
parent 6345c4ee25
commit 3ce61b47a9
1 changed files with 27 additions and 0 deletions
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27
samples/overlaydemo.c
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@ -18,16 +18,29 @@ extern void _OVERLAY2_LOAD__, _OVERLAY2_SIZE__;
extern void _OVERLAY3_LOAD__, _OVERLAY3_SIZE__; extern void _OVERLAY3_LOAD__, _OVERLAY3_SIZE__;
/* Functions resident in an overlay can call back functions resident in the
* main program at any time without any precautions. The function log() is
* an example for such a function resident in the main program.
*/
void log (char *msg) void log (char *msg)
{ {
printf ("Log: %s\n", msg); printf ("Log: %s\n", msg);
} }
/* In a real-world overlay program one would probably not use a #pragma but
* rather place the all the code of certain source files into the overlay by
* compiling them with --code-name OVERLAY1.
*/
#pragma code-name (push, "OVERLAY1"); #pragma code-name (push, "OVERLAY1");
void foo (void) void foo (void)
{ {
/* Functions resident in an overlay can access all program variables and
* constants at any time without any precautions because those are never
* placed in overlays. The string constant below is an example for such
* a constant resident in the main program.
*/
log ("Calling main from overlay 1"); log ("Calling main from overlay 1");
} }
@ -71,11 +84,25 @@ unsigned char loadfile (char *name, void *addr, void *size)
void main (void) void main (void)
{ {
log ("Calling overlay 1 from main"); log ("Calling overlay 1 from main");
/* The symbols _OVERLAY1_LOAD__ and _OVERLAY1_SIZE__ were generated by the
* linker. They contain the overlay area address and size specific to a
* certain program.
*/
if (loadfile ("ovrldemo.1", &_OVERLAY1_LOAD__, &_OVERLAY1_SIZE__)) { if (loadfile ("ovrldemo.1", &_OVERLAY1_LOAD__, &_OVERLAY1_SIZE__)) {
/* The linker makes sure that the call to foo() ends up at the right mem
* addr. However it's up to user to make sure that the - right - overlay
* is actually loaded before making the the call.
*/
foo (); foo ();
} }
log ("Calling overlay 2 from main"); log ("Calling overlay 2 from main");
/* Replacing one overlay with another one can only happen from the main
* program. This implies that an overlay can never load another overlay.
*/
if (loadfile ("ovrldemo.2", &_OVERLAY2_LOAD__, &_OVERLAY2_SIZE__)) { if (loadfile ("ovrldemo.2", &_OVERLAY2_LOAD__, &_OVERLAY2_SIZE__)) {
bar (); bar ();
} }