3.5 Data Space Selectors

OTA compilers define three types of memory area, as shown in Table 10. These
memory areas correspond to the normal set of code, initialised data, and
uninitialised data. The IDATA and UDATA selectors affect the actions of the
following words: ,, C,, ALLOT, HERE, and ALIGN (all described in Section 3.6),
CREATE (see Section 3.7), and ALIGNED (see Section 4.2). These words act on
the data area selected by the most recent use of IDATA or UDATA. The group of
affected words is referred to as the data allocation words. When the compiler
starts, the default is IDATA.

IDATA i-data I

( - )

Vector the data allocation words to refer to initialised data space. This is
the default behaviour for these words.

UDATA u-data I

( - )

Vector the data allocation words to refer to uninitialised data space. An
ambig- uous condition exists if the compiler attempts to fetch from, or store
into, unini-tialised data space.

Table 10: Memory areas in the VM

Memory Type         Selector  Contents                        Compiler Access
Initialised RAM     IDATA     Data initialised at power-up    Read/Write
Uninitialised Data  UDATA     Uninitialised data. May also    None
                              be used to define any other
                              memory-mapped region.
                                                                        

CODE, code-comma I

( x - )

Reserve one cell of initialised data space and store x in the cell. The
address will be marked as a pointer to code space for relocation.

CODE! code-store I

( x a-addr - )

Store x at a-addr in initialised data space. Mark a-addr as a pointer to
code space.

DATA! data-store I

( x a-addr - )

Store x at a-addr in initialised data space. Mark a-addr as a pointer to
initial-ised data space.

DATA, data-comma I

( x - )

Reserve one cell of initialised data space and store x in the cell. The
address will be marked as a pointer to initialised data space for
relocation.

UDATA! u-data-store I

( x a-addr - )

Store x at a-addr in initialised data space. Mark a-addr as a pointer to
unini-tialised data space.

UDATA, u-data-comma I

( x - )

Reserve one cell of initialised data space and store x in the cell. The
address will be marked as a pointer to uninitialised data space for
relocation.

EQU e-q-u H LIT <x>

( x "<spaces>name" - )

Skip leading space delimiters. Parse name delimited by a space. Create
an INTERPRETER definition for name, with the execution behaviour defined
below.

Use of EQU to define name does not affect the target image. If name is
refer-enced in a TARGET colon definition, the result will be a compiled
literal giving name's value.

An EQU may not be EXPORTed.

name Execution:( - x )

Place the value x on the stack.