3.5. Memory Directives

The * directive is used to set the program counter. A program should always start with a * directive to tell the assembler where to put the output. Here are some examples of use: 

        *=$1000 "Program"
        ldx #10
!loop:  dex
        bne !loop-
        rts

        *=$4000 "Data"
        .byte 1,0,2,0,3,0,4,0

        *=$5000 "More data"
        .text "Hello"

Note: The old notation ('.pc=$1000') from Kick Assembler 2.x and 3.x is still supported.

The last argument is optional and is used to name the memory block created by the directive. When using the ‘-showmem’ option when running the assembler a memory map will be generated that displays the memory usage and block names. The map of the above program looks like this: 

Memory Map
----------
$1000-$1005 Program
$4000-$4007 Data
$5000-$5004 More data

By using the virtual option on the .pc directive you can declare a memory block that is not saved in the resulting file. 

        *=$0400 "Data Tables 1" virtual
table1: .fill $100,0
table2: .fill $100,0

        *=$0400 "Data Tables 2" virtual
table3: .fill $150,0
table4: .fill $100,0

        *=$1000 "Program"
        ldx #0
        lda table1,x
        …

Note that virtual memory blocks can overlap other memory blocks. They are marked with an asterisk in the memory map. 

Memory Map
----------
*$0400-$05ff Data Tables 1
*$0400-$064f Data Tables 2
$1000-$1005 Program

Since virtual memory blocks aren’t saved, the above example will only save the memory from $1000 to $1005.

With the .align directive, you can align the program counter to a given interval. This is useful for optimizing your code as crossing a memory page boundary yields a penalty of one cycle for memory referring commands. To avoid this, use the .align command to align your tables: 

        *=$1000 "Program"
        ldx #1
        lda data,x
        rts

        *=$10ff       //Bad place for the data
        .align $100   //Alignment to the nearest page boundary saves a cycle
data:   .byte 1,2,3,4,5,6,7,8

In case you want your code placed at position $1000 in the memory but want it assembled like it was placed at $2000, you can use the .pseudopc directive: 

        *=$1000 "Program to be relocated at $2000"
.pseudopc $2000 {
loop:   inc $d020
        jmp loop  // Will produce jmp $2000 instead of jmp $1000
}
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