> Actually, the 6510 one is also two bytes long. If you look at the > BRK spec in e.g. the Programmer's Reference Guide, it pushes > PC+2 onto the stack; similarly, if you look at e.g. the source code > for Supermon it subtracts 2 from the PC counter on the stack to > get the correct PC. This creates a potential software feature on 6502-family processors akin to the BIOS interrupt on DOS or the toolbox traps on a Mac - use the BRK as a true SOFTWARE interrupt, and follow it by a routine vector number. Check the B bit in the status byte on the stack to see if the IRQ was triggered by a BRK instruction or a real hardware interrupt. If it was a BRK, then you use the next byte as an index into a vector table to dispatch, say, I/O requests. If you need to patch out a two byte instruction, define a double-BRK as a noop or a call to the monitor. With this scheme, you don't have to worry about kernel jump tables in ROM or any of that ugly stuff. Porting to a different 6502 design is a matter of hardware specific routines and a vector table that is known to the interrupt handler. Thoughts? -ethan - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail email@example.com.
Archive generated by hypermail 2.1.1.