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Clearer documentation on push_stack

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This commit is contained in:
Peter Evans 2018-04-13 18:01:17 -05:00
parent 3887f52119
commit 5db0c3b9c0
1 changed files with 4 additions and 10 deletions
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14
src/mos6502/mos6502.c
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@ -192,21 +192,15 @@ mos6502_free(mos6502 *cpu)
}
/*
* Push a _16-bit_ number to the stack. Generally speaking, only
* addresses are pushed to the stack, such that would be contained in
* the PC register (which is 16-bit).
*
* The stack is contained within a single page of memory, so you would
* be right in observing that the stack can contain at most 128, not
* 256, addresses.
* Push an 8-bit value to the stack, and then decrement the S register
* so that it points at the place where a new value would be deposited
* by a subsequent push. If S is decremented below 0, it rolls around to
* FF.
*/
void
mos6502_push_stack(mos6502 *cpu, vm_8bit addr)
{
mos6502_set(cpu, 0x100 + cpu->S, addr);
// And finally we need to increment S by 2 (since we've used two
// bytes in the stack).
cpu->S--;
}