Paul wrote:
>I often use the stack pointer for storage in a tight kernel (using TSX/TXS). It's handy when you need to save the value of X temporarily, and can often shave off a few cycles. Just make sure that if you use the stack in your program, that you save the stack pointer value beforehand and restore it afterwards.
Really? Can you give a practical example?
I've always considered it too awkward to be of real use:
TXS
TSX
4 cycles
STX $ZeroPage
LDX $ZeroPage
6 cycles
Savings = 2 cycles
However,
TSX
STX $ZeroPage
...
TXS
...
TSX
...
LDX $ZeroPage
TXS
14 cycles
Unless your swapping out of X is really timing critical but you can spare the cycles required to save/restore the stack. Or you've got a stack free program. Or you have no scratch RAM available.
Hmmm...
Chris...
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