ABSOLUTE directive can be thought of as an alternative form of
SECTION: it causes the subsequent code to be directed at no
physical section, but at the hypothetical section starting at the given absolute address.
The only instructions you can use in this mode are the
ABSOLUTE is used as follows:
ABSOLUTE 0x1A kbuf_chr resw 1 kbuf_free resw 1 kbuf resw 16
This example describes a section of the PC BIOS data area, at segment address 0x40:
the above code defines
kbuf_chr to be 0x1A,
kbuf_free to be 0x1C, and
kbuf to be
ABSOLUTE doesn’t have to take an absolute constant as
an argument: it can take an expression (actually, a critical expression: see Section 3.8) and it can be a
value in a segment. For example, a TSR can re-use its setup code as run-time BSS like
org 100h ; it's a .COM program jmp setup ; setup code comes last ; the resident part of the TSR goes here setup: ; now write the code that installs the TSR here absolute setup runtimevar1 resw 1 runtimevar2 resd 20 tsr_end:
This defines some variables “on top of” the setup code, so that after the setup has finished running, the space it took up can be re-used as data storage for the running TSR. The symbol “tsr_end” can be used to calculate the total size of the part of the TSR that needs to be made resident.