Gameboy Development Forum

for those who do not participate discord.

there are tremendous changes in SDCC made recent couple of weeks.

1. first of all, sdldgb linker and makebin utility are put into a working state. all __banked stuff is working from the box, there is no need for link-gbz80 anymore.

1.1. a new method of calling banked functions is introduced, which passes far pointer in E:HL, that results in more efficient trampoline functions and increase performance.

1.2. makebin has some new commandline arguments for gb

2. sdcc optimizer tries to allocate variables into registers with more enthusiasm. that results into big gain to the code performance. here is a comparison i made for genesis game from 0x7f:


2.2. thare are also much better rules for peephole optimizer, as built in, also third party: https://github.com/basxto/gbz80-ph

3. RGBDS mappings are fixed. you may use RGBDS assembler and linker https://rednex.github.io/rgbds/ as a backend for SDCC compiler. i even made a simple proto-library https://github.com/untoxa/RGBDK.git

all those improvements are already avaliable in revision #11777 or higher of SDCC, snapshot may be downloaded here: http://sdcc.sourceforge.net/snap.php

also: 

4. in future releases __z88dk_fastcall calling convention might be allowed for gb target - that give some extra gain for single-parameter functions, because that parameter is passed in registers.

all that improvements became possible with the help of SDCC team: Philipp Klaus Krause, Sebastian Riedel, Sergey Belyashov; we we are looking forward for the new features.

unfortunately, current version of GBDK-2020 became unusable. those enhancements triggered usage of XL3 object file format which is not compatible with the old link-gbz80 linker.

but if you don't use lcc, then you have an ability to compile your sources directly by calling sdcc, sdasgb, sdldgb and makebin. you may also use a pre-compiled version of gbdk-2020 library, sdldgb is backward-compatible with older object files.

also you might need a new trampoline function, here it is: ___sdcc_bcall_ehl.s

    .include    "global.s"

    .area _BASE

___sdcc_bcall_ehl::            ; Performs a long call.
ldh a,(__current_bank)
    push    af            ; Push the current bank onto the stack
    ld    a, e
    ldh    (__current_bank),a
    ld    (.MBC1_ROM_PAGE),a    ; Perform the switch
    rst    0x20
    pop    af            ; Pop the old bank
    ld    (.MBC1_ROM_PAGE),a
    ldh    (__current_bank),a
    ret

Last edited by toxa (2020-07-28 16:17:41)