Allocating memory in RAM outside ZP

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zanto
Posts: 57
Joined: Sun Mar 07, 2021 11:15 pm
Location: Rio de Janeiro, Brazil

Allocating memory in RAM outside ZP

Post by zanto » Wed Mar 10, 2021 10:01 pm

I can allocate memory in the zero page by executing the code:

Code: Select all

.segment "ZEROPAGE"		
var1:		.res 1
var2:		.res 1
But I want to know how to allocate memory in RAM outside ZP. I saw in an example code:

Code: Select all

.segment "BSS"
nmt_update: .res 256 ; nametable update entry buffer for PPU update
palette:    .res 32  ; palette buffer for PPU update
But I think I misunderstood it, because when I tried doing the same in my code, it was allocating memory at address $6000. I use cc65, so I checked nes.cfg to see if it gave me a hint, but I couldn't find anything

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SYMBOLS {
    __STACKSIZE__: type = weak, value = $0300; # 3 pages stack
}
MEMORY {
    ZP:     file = "", start = $0000, size = $00FF, type = rw, define = yes;

    # INES Cartridge Header
    HEADER: file = %O, start = $0000, size = $0010, fill = yes;

    # 2 16K ROM Banks
    # - startup
    # - code
    # - rodata
    # - data (load)
    ROM0:   file = %O, start = $8000, size = $7FFA, fill = yes, define = yes;

    # Hardware Vectors at End of 2nd 8K ROM
    ROMV:   file = %O, start = $FFFA, size = $0006, fill = yes;

    # 1 8k CHR Bank
    ROM2:   file = %O, start = $0000, size = $2000, fill = yes;

    # standard 2k SRAM (-zeropage)
    # $0100-$0200 cpu stack
    # $0200-$0500 3 pages for ppu memory write buffer
    # $0500-$0800 3 pages for cc65 parameter stack
    SRAM:   file = "", start = $0500, size = __STACKSIZE__, define = yes;

    # additional 8K SRAM Bank
    # - data (run)
    # - bss
    # - heap
    RAM:    file = "", start = $6000, size = $2000, define = yes;
}
SEGMENTS {
    ZEROPAGE: load = ZP,              type = zp;
    HEADER:   load = HEADER,          type = ro;
    STARTUP:  load = ROM0,            type = ro,  define   = yes;
    LOWCODE:  load = ROM0,            type = ro,  optional = yes;
    ONCE:     load = ROM0,            type = ro,  optional = yes;
    CODE:     load = ROM0,            type = ro,  define   = yes;
    RODATA:   load = ROM0,            type = ro,  define   = yes;
    DATA:     load = ROM0, run = RAM, type = rw,  define   = yes;
    VECTORS:  load = ROMV,            type = rw;
    CHARS:    load = ROM2,            type = rw;
    BSS:      load = RAM,             type = bss, define   = yes;
}
FEATURES {
    CONDES: type    = constructor,
            label   = __CONSTRUCTOR_TABLE__,
            count   = __CONSTRUCTOR_COUNT__,
            segment = ONCE;
    CONDES: type    = destructor,
            label   = __DESTRUCTOR_TABLE__,
            count   = __DESTRUCTOR_COUNT__,
            segment = RODATA;
    CONDES: type    = interruptor,
            label   = __INTERRUPTOR_TABLE__,
            count   = __INTERRUPTOR_COUNT__,
            segment = RODATA,
            import  = __CALLIRQ__;
}
I thought about checking nes.cfg because I had to edit it once in the past to properly setup the zero page address range (it came as $0000-$001F or something by default)



EDIT: I found another .cfg file that fixes the problem. I replaced the one that came with cc65 with it and now everything works

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MEMORY {
    ZP:     start = $00,    size = $0100, type = rw, file = "";
    OAM:    start = $0200,  size = $0100, type = rw, file = "";
    RAM:    start = $0300,  size = $0500, type = rw, file = "";
    HDR:    start = $0000,  size = $0010, type = ro, file = %O, fill = yes, fillval = $00;
    PRG:    start = $8000,  size = $8000, type = ro, file = %O, fill = yes, fillval = $00;
    CHR:    start = $0000,  size = $2000, type = ro, file = %O, fill = yes, fillval = $00;
}

SEGMENTS {
    ZEROPAGE: load = ZP,  type = zp;
    OAM:      load = OAM, type = bss, align = $100;
    BSS:      load = RAM, type = bss;
    HEADER:   load = HDR, type = ro;
    CODE:     load = PRG, type = ro,  start = $8000;
    RODATA:   load = PRG, type = ro;
    VECTORS:  load = PRG, type = ro,  start = $FFFA;
    TILES:    load = CHR, type = ro;
}
I thought about deleting the post, but I figured this may be helpful to someone else in the future :)

lidnariq
Posts: 10459
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: Allocating memory in RAM outside ZP

Post by lidnariq » Wed Mar 10, 2021 10:21 pm

zanto wrote:
Wed Mar 10, 2021 10:01 pm
But I want to know how to allocate memory in RAM outside ZP. I saw in an example code:

Code: Select all

.segment "BSS"
nmt_update: .res 256 ; nametable update entry buffer for PPU update
palette:    .res 32  ; palette buffer for PPU update
[...]
I checked nes.cfg to see if it gave me a hint, but I couldn't find anything

Code: Select all

[...]
MEMORY {
[...]
    RAM:    file = "", start = $6000, size = $2000, define = yes;
}
SEGMENTS {
[...]
    BSS:      load = RAM,             type = bss, define   = yes;
}
The above excerpts are why allocations into BSS are at $6000. (segment "BSS" is "load"ed into "RAM"; memory "RAM" starts at $6000)

User avatar
tokumaru
Posts: 12054
Joined: Sat Feb 12, 2005 9:43 pm
Location: Rio de Janeiro - Brazil

Re: Allocating memory in RAM outside ZP

Post by tokumaru » Wed Mar 10, 2021 11:52 pm

We generally make our own .cfg files, because everyone's needs are different. You can of course use someone else's .cfg file and write your program in a similar style to that person's, but you can also write your own .cfg files according to your own programming style. I for example don't like to start from $300 and go up until $7FF, I like to select what goes in each page so I can optimize access to large arrays.

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