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System Initialization and Acceptance Testing (Normal Operation)
4.7 Operating System Bootstrap
On the KA681/KA691/KA692/KA694 a bootstrap occurs whenever a BOOT
command is issued at the console or whenever the processor halts and the
conditions specified in Table 3–5 for automatic bootstrap are satisfied.
4.7.1 Preparing for the Bootstrap
Prior to dispatching to the primary bootstrap (VMB), the firmware initializes
the system to a known state. The initialization sequence follows:
1. Check the console program mailbox "bootstrap in progress" bit
(CPMBX<2>(BIP)). If it is set, bootstrap fails.
2. If this is an automatic bootstrap, display the message "Loading system
software." on the console terminal.
3. Set CPMBX<2>(BIP).
4. Validate the Page Frame Number (PFN) bitmap. If PFN bitmap checksum
is invalid, then:
a. Perform an UNJAM.
b. Perform an INIT.
c. Retest memory and rebuild PFN bitmap.
5. Validate the boot device name. If none exists, supply a list of available
devices and prompt user for a device. If no device is entered within 30
seconds, use EZA0.
6. Write a form of this BOOT request including the active boot flags and boot
device on the console, for example "(BOOT/R5:0 DUA0)".
7. Initialize the Q22–bus scatter/gather map.
a. Set IPCR<8>(AUX_HLT).
b. Clear IPCR<5>(LMEAE).
c. Perform an UNJAM.
d. Perform an INIT.
e. If an arbiter, map all vacant Q22–bus pages to the corresponding page
in local memory and validate each entry if that page is "good".
f. Set IPCR<5>(LMEAE).
8. Search for a 128 KB contiguous block of good memory as defined by the
PFN bitmap. If 128 KB cannot be found, the bootstrap fails.
4–24 System Initialization and Acceptance Testing (Normal Operation)