HP 64783A, Руководство пользователя

Страница: 419 / 816

Example to show resource limitations
Consider the following program arrangement:
Assume a system contains memory and peripherals at three different ranges: one
from 0 to 4 Mbytes, one from 256 to 258 Mbytes, and one from 512 to 514 Mbytes.
The rest of the physical address space is unused.
If your MMU mapping tables are set up to only allow access to memory in these
ranges, your deMMUer will load properly and you can proceed with your
measurements. If you failed to restrict your MMU mappings to these physical
ranges (instead you provided valid address translations for the entire 4-Gbyte
address space), the deMMUer will allocate all eight of its resource blocks in the
first 256-Mbyte range, and no deMMUing will be provided for the peripherals and
ROM space in the above program.
The Emulation Memory Map Can Help
When the emulator tries to load the deMMUer and finds more physical memory
identified in the MMU mapping tables than it can translate in its deMMUer table, it
will assign resources to terms defined in the emulation memory map. If the
emulation memory map is arranged as follows, the deMMUer will load in a way
that ensures the physical ranges of interest will be in the deMMUer.
0 to 3FFFFFH EMUL/RAM
10000000H to 101FFFFFH TARGET/RAM
20000000H to 203FFFFFH TARGET/ROM
default TARGET RAM
When the emulator reads the emulation memory map for help in loading the
deMMUer, it sorts the entries: first by size, and second by address range. The
smallest address range (256M to 258M) will occupy the first resource block in the
deMMUer translation table. Address range (0 to 4M) will occupy the second
resource block, and address range (512M to 514M) will occupy the third resource
block. The remaining five resource blocks will be assigned to other physical ranges
found in the MMU tables, beginning with the lowest addresses. You may see a
message indicating some physical addresses will not be translated by the
4M RAM Unused 2M Peripherals Unused 4M ROM Unused
0 4M 256M 258M 512M 514M
Chapter 10: Using Memory Management
Using the DeMMUer
389