Re: [pups] Major/minor device numbers and device names for MSCP drives?

Robert Armstrong wrote: This is what I remember about it all when I struggled with it a couple of years ago. The 8 bit minor number has 3 parts: the upper two bits are the controller (4 controllers max), the middle 3 bits are unit number (8 drives per controller) and the lower 3 bits are the partition (a-h). The assignment of device names is static (or nearly static). The discovery code for the controllers checks them in the order listed in /dev/dtab and assigns a controller number to each that is discovered and in that order (the nearly static part). Note also that DEC has a standard order for controller addresses too (which might be different). After that, drives are accessed using the 3 bit unit number which MUST correspond to the MSCP unit number (a catch follows because of this). Partitions are accessed with the 3 bit partition number. The catch is that MSCP unit numbers are supposed to be global cross all controllers and the microPDP-11/83 boot code assumes this. The boot code can only see the first unit n that is encountered and 2.11BSD can only see the drives with MSCP unit numbers less than 8. If you only have one controller there is no problem. When you add multiple controllers, things get more complex because you can only boot the first 8 MSCP units if you want to be able to access them from 2.11BSD. -chuck