I'm guessing they reimplemented the toolbox at the TRAP level (most MacOS calls at the time were accessed through the 68K TRAP instruction).
So, rather than emulating hardware to run native ROMs, they "simply" reimplemented the ROMs.
A friend of mine did this at another level. He basically rewrote the bulk of the toolbox as a C library so that the company, who had a Mac application, could port it to run on a PC, while sharing the source code.
This was before Windows, and it worked! Launched it from DOS, takes over the entire screen. He didn't copy the Mac look and feel. Instead he used OpenLook for his gadgets and what not (since it was, you know, "open").
But he rewrote the bulk of it: QuickDraw, Event Manager, Memory Manager, Window Manager, etc. Just ate it like an elephant. I don't think his regions were as clever as the Mac. Pretty sure he just stuck with rectangles.
Correction: 68K Mac OS calls were A-line traps — in other words, they had opcodes of the form `$Axxx`. To the processor, they're unimplemented instructions that each take an exception through the same vector. The exception handler is the Mac OS trap dispatcher.
`TRAP` is a different instruction, with opcodes `$4E4x`. Each one gets its own exception vector.
It's not just trap calls, though — sometimes applications write directly to the sound buffer or use hardware page flipping.
As I recall MacOS system calls were done through invalid instructions which would cause the CPU to "trap" (raise an interrupt). Giving rise to the question Mac extension writers asked of each other: "How many traps did you patch?"
My earliest recollection of what motivated me is a desire to resurrect The Fool's Errand.
The irony is not lost on me. :-)
I'm guessing they reimplemented the toolbox at the TRAP level (most MacOS calls at the time were accessed through the 68K TRAP instruction).
So, rather than emulating hardware to run native ROMs, they "simply" reimplemented the ROMs.
A friend of mine did this at another level. He basically rewrote the bulk of the toolbox as a C library so that the company, who had a Mac application, could port it to run on a PC, while sharing the source code.
This was before Windows, and it worked! Launched it from DOS, takes over the entire screen. He didn't copy the Mac look and feel. Instead he used OpenLook for his gadgets and what not (since it was, you know, "open").
But he rewrote the bulk of it: QuickDraw, Event Manager, Memory Manager, Window Manager, etc. Just ate it like an elephant. I don't think his regions were as clever as the Mac. Pretty sure he just stuck with rectangles.
Correction: 68K Mac OS calls were A-line traps — in other words, they had opcodes of the form `$Axxx`. To the processor, they're unimplemented instructions that each take an exception through the same vector. The exception handler is the Mac OS trap dispatcher.
`TRAP` is a different instruction, with opcodes `$4E4x`. Each one gets its own exception vector.
It's not just trap calls, though — sometimes applications write directly to the sound buffer or use hardware page flipping.
As I recall MacOS system calls were done through invalid instructions which would cause the CPU to "trap" (raise an interrupt). Giving rise to the question Mac extension writers asked of each other: "How many traps did you patch?"