HP 64783A, User Manual

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Providing MMU Address Translation for the
Foreground Monitor
When using the memory management unit (MMU) of the MC68040, the target
system must provide the proper address translation for the foreground monitor. To
be able to do this, you will need to understand your target system’s physical
memory map and MMU address translation structure. You may need to modify
your mapping scheme or some of its mapping protections.
In order for the monitor to operate after the MMU is turned on, the target system
must provide 1:1 address translation (logical address = physical address) for the
block of memory occupied by the monitor. The foreground monitor will reside in a
4-Kbyte block of emulation memory corresponding to a single page in the MMU.
This memory can be mapped to begin on any 4-Kbyte address boundary. Simply
specify an address ending in 000h when you answer the monitor address question
when you set up the emulation configuration.
For example, if the monitor is located at logical address 0ffff1000h, then the MMU
must translate that address to physical address 0ffff1000h, logical address
0ffff1004h to physical address 0ffff1004h, etc.
Do not write-protect the address range occupied by the foreground monitor.
There are two ways to provide the proper address translation for the memory space
occupied by the foreground monitor:
•
Locate the foreground monitor in a block of memory that is transparently
translated via ITTx and DTTx transparent translation registers (TTRs). The
monitor contains both code and data so two TTRs are needed to provide
translations: one for instructions, and the other for data. When the MMU
processes translations, it first compares the logical address with the parameters
of the TTRs. If it finds a match, the MMU uses the logical address as the
physical address for the access (obtaining the needed 1:1 translation).
The minimum block size that can be transparently translated by the TTRs is 16
Mbytes. If your target system already sets one or both data and instruction
TTRs for supervisor, or both supervisor and user, access and no
write-protection, then you may be able to find an unused 4-Kbyte block within
this 16-Mbyte range where the monitor can reside.
Chapter 8: Configuring the Emulator
Providing MMU Address Translation for the Foreground Monitor
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