System Initialization and Acceptance Testing (Normal Operation)
4.7 Operating System Bootstrap
Figure 4–5 Boot Block Format
any value
high LBN
low LBN
n
1
CHK
k
18 (Hex)
any value, most likely 0
size in blocks of the image
load offset
offset into image to start
sum of the previous three longwords
(The next segment is also used as a PROM "signature block.")
31
24 23
16 15
BB+(2*n)+20:
BB+(2*n)+16:
BB+(2*n)+12:
BB+(2*n)+8:
BB+(2*n)+0:
BB-0:
Where:
1) the 18 (hex) indicates this is a VAX instruction set
2) 18 (hex) + "k" = the one’s complement if "CHK"
0
0
MLO-008457
4.7.3.2 PROM Bootstrap Procedure
The PROM bootstrap uses a variant of the boot block mechanism. VMB
searches for a valid PROM "signature block", the second segment of the boot
block defined in Figure 4–5. If PRA0 is the selected "device", then VMB
searches through Q22–bus memory on 16 KB boundaries. If the selected
"device" is PRB0, VMB checks the top 4096 byte block of the FEPROM.
At each boundary, VMB :
1. Validates the readability of that Q22–bus memory page.
2. If readable, checks to see if it contains a valid PROM signature block.
If verification passes, the PROM image will be copied into main memory and
VMB will transfer control to that image at the offset specified in the PROM
bootblock. If not, the next page will be tested.
System Initialization and Acceptance Testing (Normal Operation)
4–31
