eZ80 CPU - writeframeofmind.biz

eZ80 CPU
User Manual
12
Mixed-ADL Applications
Applications that include legacy routines/functions/tasks/modules that run in
non-ADL mode and new routines/functions/tasks/modules that run in ADL
mode, must follow certain rules to ensure proper operation:
• Include a STMIX instruction in device initialization to ensure that interrupt
service routines begin in a consistent mode (ADL mode).
• End all interrupt service routines with a prefixed RET or RETI instruction,
which pops the interrupted code's ADL state from the SPL stack.
• CALL or JP to each routine/function/task/module in the mode in which it
was assembled or compiled.
• Any routine that may be called from either mode must be called with a prefix
to save the caller's ADL mode on the SPL stack.
• Any routine that may be called from either mode must return with a prefixed
RET instruction to restore the caller's ADL state from the SPL stack.
• If a calling code operating in one mode must pass stack-based operands/
arguments to a routine compiled or assembled for a different mode, it must
use prefixed instructions to set up the operands/arguments. For PUSH, .S
and .L prefixes control whether SPS or SPL is used and whether the
operands/ arguments are stored as 2- or 3-byte values.
Note: In mixed-ADL applications, some of the rules above may represent exceptions to the eZ80's design
goal that legacy code not have to be modified to be run on the eZ80. Assuming that legacy routines
are not selectively converted to ADL mode and that legacy routines don't call newly written routines,
the only rule that would lead to such modification would be the fifth rule above. If each legacy routine
ends with a single RET at its end, this conversion is easy. Internal and conditional RETs require more
careful review -- a program to highlight RETs may be helpful.
Prefix Bytes: Exceptions to ADL Mode
In the ZiLOG ZMASM / ZDS assembler, code is assembled for a given state of
the ADL mode bit by preceding it with a pseudo-op:
.assume adl=1 ; or adl=0
You are, of course, responsible for ensuring that this source file setting matches
the state of the hardware ADL mode bit when the code is executed.
The ADL mode and assumed setting govern several different aspects of
instruction and eZ80 operation, as described in preceding sections. Two
different kinds of exceptions to normal operation can be selected for a particular
instruction by adding a suffix to the instruction’s Op Code.
UM007701-1100