Offset Registers - Motorola MVME166IG/D2 Installation Manual

Using the 166Bug Debugger
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Offset Registers

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Eight pseudo-registers (R0 through R7) called offset registers are used to
simplify the debugging of relocatable and position-independent modules.
The listing files in these types of programs usually start at an address
(normally 0) that is not the one at which they are loaded, so it is harder to
correlate addresses in the listing with addresses in the loaded program. The
offset registers solve this problem by taking into account this difference and
forcing the display of addresses in a relative address+offset format. Offset
registers have adjustable ranges and may even have overlapping ranges. The
range for each offset register is set by two addresses: base and top. Specifying
the base and top addresses for an offset register sets its range. In the event that
an address falls in two or more offset registers' ranges, the one that yields the
least offset is chosen.
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In commands with RANGE specified as ADDR DEL ADDR,
and with size option W or L chosen, data at the second
(ending) address is acted on only if the second address is a
proper boundary for a word or longword, respectively.
Relative addresses are limited to 1MB (5 digits), regardless
of the range of the closest offset register.
MVME166 Single Board Computer Installation Guide