Back in the PC clone days the accepted legally defensible method of selling a non-IBM PC BIOS was using a "clean room" whereby an engineer who had never been exposed to proprietary IBM information was given detailed "specifications" by another group who had studied the IBM PC architecture and available technical references, including the published BIOS source code.
What specific pieces of information were "off limits" to the "clean" engineer tasked with writing the actual BIOS code?
Would they be able to read and reference the IBM Technical References with the BIOS source code pages removed?
Could they reference electrical schematics or the logic diagrams included in the Technical Reference during development?
Was it permitted to ask additional clarifying questions of the team who wrote the specifications originally?
Would they be able to browse their own disassembly the ROMs on a retail-purchased IBM PC? What about tracing and observing BIOS call responses with a tool such as DEBUG?
What about being able to use a scope or logic analyzer on a retail IBM PC?
If the engineer had ever browsed the IBM Technical Manual (say in their personal life before the project started), would that permanently or temporarily disqualify them from ever being able to work in that capacity in their lifetime? Memories fade and I know that if I did a code review a year or more ago -- especially not with the goal in mind of ever being able to reproduce the work later, there's no way I could today remember more than the most cursory of details about it.
Were code reviews permitted by the engineers who wrote the specs?
How detailed were these "specifications" permitted to be? As in, could you only say "INT 14 takes port in
DXand parameters in
ALand returns these values in so and so registers in flags"? Or could it be more like pseudocode "first, send control byte
3FBto set baud rate, then send high byte to port
3F9... etc, etc"?
Not looking for specific answers to each question - just using examples to try to understand where exactly the line was considered drawn. I'd expect some of the answers might be the intuitive "if any doubt, better safe than sorry and take them off the project". However, I'm wondering as much about the actual standards and practices that were in place that allowed companies like Award, AMI, Phoenix, Compaq, etc to successfully productize and sell clone BIOSes.