Zilog Z8F0130 - Manual (Page 224)

Using the ANSI C-Compiler UM013037-1212
200
Zilog Developer Studio II – Z8 Encore!
User Manual
printf() usually cannot be used with the small model because the stack grows too large
and corrupts the data.
Large Memory Model
In the large memory model, global variables are allocated in the EData address space. The
address of these variables is 16 bits. The locals and parameters are allocated on the stack,
which is also located in the EData address space. The address of a local or parameter is a
16-bit address. Global variables can be manually placed into the RData or ROM address
space by using the address specifiers
near or rom , respectively. Local (nonstatic) vari-
ables and parameters are always allocated in the EData address space, and any address
specifiers used in their declarations are ignored.
If you are forced to use the large model because of your data space and stack requirements,
you can still get some of the benefit of the more efficient code that is typical of the small
model. To do so, carefully choose the most frequently used global or static variables and
declare them
near . This helps with both code size and even more so with execution speed
because more frequently executed code is more efficient.
One way of minimizing the amount of data space (RData and EData) your application
needs is to allocate a single buffer in data space to hold, for example, the largest of a num-
ber of strings you might need to display. The numerous strings are stored permanently in
ROM, where space is often less limited. Each string, in turn, is then copied from ROM to
data space at the moment when it is needed.
Another way of saving space when data space (RData and EData) is at a premium is to
declare initialized tables that are not modified in the code with the
rom keyword. The
trade-off here is that the execution speed is likely to be somewhat slower because the num-
ber of addressing modes available to the compiler for accessing
rom variables is very
small.
Call Frames
Call frames hold the arguments, local variables, and other pertinent information of an
instantiation of a procedure or function at a time. The Zilog Z8 Encore! C-Compiler sup-
ports two types of call frames:
•
Static Frames – see page 201
•
Dynamic Frames – see page 201
Note: