From Intellivision Wiki
|Entry point||Function provided||Notes|
|SCRATCH||Allocate storage in 8-bit Scratchpad RAM||Allocated range will be in 8-bit memory from $102 - $1EF.|
|SYSTEM||Allocate storage in 16-bit System RAM||Allocated range will be in 16-bit memory from $2F0 - $35F.|
See source code below for calling convention.
(todo... please contribute!)
These routines expect to have sole authority over how the 8-bit Scratchpad RAM and 16-bit System RAM are allocated. They are not compatible with programs that use the EXEC, as the EXEC reserves some of these locations to itself. The SCRATCH macro does not disturb the interrupt service vector at $100 - $101.
When using this scheme, you should use the SYSTEM macro to declare a stack, and set the stack pointer (R6) to point to this stack early in your initialization. For instance:
STACK SYSTEM 32 ; Reserve 32 words of stack space MVII #STACK, R6 ; Initialize stack pointer
Note that you will effectively lose the previous contents of your stack when you do this, which is why it should be one of the first things you do in your initialization.
To get an idea of how much Scratchpad RAM and System RAM your program uses, look for the symbols ".SCRMEM" and ".SYSMEM" in the assembler listing file or symbol dump file. .SCRMEM indicates the first free location of Scratchpad RAM, and .SYSMEM indicates the first free location of System RAM. The macros allocate from the bottom of memory toward the top. Therefore, $1F0 - .SCRMEM gives the remaining amount of 8-bit Scratchpad RAM, and $360 - .SYSMEM gives the remaining amount of 16-bit System RAM.
;* ======================================================================== *; ;* These routines are placed into the public domain by their author. All *; ;* copyright rights are hereby relinquished on the routines and data in *; ;* this file. -- Joseph Zbiciak, 2008 *; ;* ======================================================================== *; IF (DEFINED _DSEG_MAC) == 0 _DSEG_MAC EQU 1 ;; ======================================================================== ;; ;; SCRATCH Declare a variable in 8-bit (scratch) memory ;; ;; SYSTEM Declare a variable in 16-bit (system) memory ;; ;; ;; ;; These macros provide a convenient method for declaring variables in the ;; ;; Intellivision's internal memory. Rather than rely on EQUs and one's ;; ;; own memory, you can use these macros to declare your variables in RAM. ;; ;; ;; ;; Both work identically, with the only difference being which pool of ;; ;; memory the variable gets allocated in. SCRATCH allocates storage in ;; ;; 8-bit memory at $102 through $1EF. SYSTEM allocates storage in 16-bit ;; ;; memory at $2F0 through $35F. ;; ;; ;; ;; Both macros expect to own the entire pool. If you manually allocate ;; ;; some addresses in either range and use these macros, the two may clash. ;; ;; You will need to adapt these to skip those addresses, or change the ;; ;; manual allocations to use these macros. ;; ;; ;; ;; USAGE ;; ;; ;; ;; label SCRATCH len ;; ;; label SYSTEM len ;; ;; ;; ;; where 'label' is the name of the label to associate with the memory ;; ;; range, and 'len' is how many locations to set aside (typically 1). ;; ;; ;; ;; EXAMPLES ;; ;; ;; ;; FLAG SCRATCH 1 ; Allocate 1 8-bit location, named "FLAG" ;; ;; STACK SYSTEM 32 ; Allocate 32 16-bit locations, named "STACK" ;; ;; ;; ;; Note: For the "STACK" example, this won't place your stack there ;; ;; unless you also do "MVII #STACK, R6" to relocate your stack. ;; ;; ======================================================================== ;; .SCRMEM SET $102 .SYSMEM SET $2F0 MACRO SCRATCH l EQU .SCRMEM LISTING "off" .SCRMEM SET .SCRMEM + %l% IF .SCRMEM > $1F0 ERR "Scratch Memory Overflow" ENDI LISTING "prev" ENDM MACRO SYSTEM l EQU .SYSMEM LISTING "off" .SYSMEM SET .SYSMEM + %l% IF .SYSMEM > $360 ERR "System Memory Overflow" ENDI LISTING "prev" ENDM ENDI ;; ======================================================================== ;; ;; End of File: dseg.mac ;; ;; ======================================================================== ;;