User`s guide

System Initialization and Acceptance Testing (Normal Operation)
4.7 Operating System Bootstrap
VMB inherits a well defined environment and is responsible for further
initialization. The following summarizes the operation of VMB.
1. Initialize a two-page SCB on the first-page boundary above VMB.
2. Allocate a three-page stack above the SCB.
3. Initialize the Restart Parameter Block (RPB).
4. Initialize the secondary bootstrap argument list.
5. If not a PROM boot, locate a minimum of three consecutive valid QMRs.
6. Write "2" to the diagnostic LEDs and display "2.." on the console to indicate
that VMB is searching for the device.
7. Optionally, solicit from the console a "Bootfile: " name.
8. Write the name of the boot device from which VMB will attempt to boot on
the console, for example, "-DIA0".
9. Copy the secondary bootstrap from the boot device into local memory above
the stack. If this fails, the bootstrap fails.
10. Write "1" to the diagnostic LEDs and display "1.." on the console to indicate
that VMB has found the secondary bootstrap image on the boot device and
has loaded the image into local memory.
11. Clear CPMBX<2>(BIP) and CPMBX<3>(RIP).
12. Write "0" to the diagnostic LEDs and display "0.." on the console to indicate
that VMB is now transferring control to the loaded image.
13. Transfer control to the loaded image with the following register usage.
R5 Transfer address in secondary bootstrap image
R10 Base address of secondary bootstrap memory
R11 Base address of RPB
AP Base address of secondary boot parameter block
SP Base address of secondary boot parameter block
If the bootstrap operation fails, VMB relinquishes control to the console
by halting with a HALT instruction. VMB makes no assumptions about
the location of Q22–bus memory. However, VMB searches through the
Q22–bus Map Registers (QMRs) for the first QMR marked "valid". VMB
requires minimally 3 and maximally 129 contiguous "valid" maps to complete a
bootstrap operation. If the search exhausts all map registers or there are fewer
than the required number of "valid" maps, a bootstrap cannot be performed.
It is recommended that a suitable block of Q22–bus memory address space be
4–24 System Initialization and Acceptance Testing (Normal Operation)