What is SPMC65 stack mapping?
The SPMC65 stack contains 32-byte. At least 3-byte is needed for one interrupt context saving: 2 bytes for return address and 1 byte for the status register. Before entering an interrupt, A, X, Y are often pushed into stack, too. Therefore, 6 bytes of memory are often required and at most 5 layer interrupts are embedded. 2 bytes are occupied for a subroutine, therefore, 16 layers at most are embedded. If the stack is out of default memory, illegal address interrupt will occur.
