User`s guide

Data Structures and Memory Layout
C.2 Restart Parameter Block
Table C–2 (Cont.) Restart Parameter Block Fields
(R11)+ Field Name Description
44: RPB$Q_PFNMAP The PFN bitmap is an array of bits, where
each bit has the value "1" if the corresponding
page of memory is valid, or has the value "0"
if the corresponding page of memory contains
a memory error. Through use of the PFNMAP,
the operating system can avoid memory errors
by avoiding known bad pages altogether.
The memory bitmap is always page-aligned,
and describes all the pages of memory from
physical page #0 to the high end of memory,
but excluding the PFN bitmap itself and the
Q–bus map registers. If the high byte of the
bitmap spans some pages available to the
operating system and some pages of the PFN
bitmap itself, the pages corresponding to the
bitmap itself will be marked as bad pages.
The first longword of the PFNMAP descriptor
contains the number of bytes in the PFNMAP;
the second longword contains the physical
address of the bitmap.
4C: RPB$L_PFNCNT Count of "good" pages of physical memory,
but not including the pages allocated to the
Q22–bus scatter/gather map, the console
scratch area, and the PFN bitmap at the
top of memory.
50: RPB$L_SVASPT 0.
54: RPB$L_CSRPHY Physical address of CSR for boot device.
58: RPB$L_CSRVIR 0.
5C: RPB$L_ADPPHY Physical address of ADP (really the address of
QMRs - ^x800 to look like a UBA adapter).
60: RPB$L_ADPVIR 0.
64: RPB$W_UNIT Unit number of boot device.
66: RPB$B_DEVTYP Device type code of boot device.
67: RPB$B_SLAVE Slave number of boot device.
68: RPB$T_FILE Name of secondary bootstrap image (defaults
to [SYS0.SYSEXE]SYSBOOT.EXE). This field
(up to 40 bytes) is overwritten with the input
string on a ‘‘solicit’’ boot.
(continued on next page)
Data Structures and Memory Layout C–7