Target
From MSX Game Library
The choice of the target determines the final format of the game: ROM, disk, etc.
It is a parameter used by the Build Tool to adapt your code to the target during the construction of the final program and to assemble the data to be compatible with the target.
The choice of the format is made in the project configuration file (project_config.js).
Here is a description of the different target formats available in MSXgl.
Contents
Basic program
Binary program to be executed from the BASIC environment using bload function.
| Target | Description |
|---|---|
| BIN | BASIC binary program (starting at 8000h) |
| BIN_USR | BASIC USR binary driver (starting at C000h) |
| BAS | Alias for BIN |
Note: The maximum size of a BASIC program is about 24 KB (including variables).
MSX-DOS program
Binary program to be executed from the MSX-DOS environment.
| Target | Description |
|---|---|
| DOS1 | MSX-DOS 1 program (starting at 0100h) |
| DOS2 | MSX-DOS 2 program (starting at 0100h) |
| DOS | Alias for DOS1 |
| DOS0 | Direct program boot from disk (starting at 0100h) |
| BOOT | Alias for DOS0 |
Note:
- The maximum size of a MSX-DOS program is about 53 KB (including variables).
- For "DOS0" target, maximum is 48 KB (excluding variables).
Plain ROM program
| Target | Description |
|---|---|
| ROM_8K | 8 KB ROM in page 1 (4000h ~ 5FFFh) |
| ROM_8K_P2 | 8 KB ROM in page 2 (8000h ~ 9FFFh) |
| ROM_16K | 16 KB ROM in page 1 (4000h ~ 7FFFh) |
| ROM_16K_P2 | 16 KB ROM in page 2 (8000h ~ BFFFh) |
| ROM_32K | 32 KB ROM in page 1&2 (4000h ~ BFFFh) |
| ROM_48K | 48 KB ROM in page 0-2 (0000h ~ BFFFh) |
| ROM_48K_ISR | 48 KB ROM in page 0-2 (0000h ~ BFFFh) with ISR replacement |
| ROM_64K | 64 KB ROM in page 0-3 (0000h ~ FFFFh) |
| ROM_64K_ISR | 64 KB ROM in page 0-3 (0000h ~ FFFFh) with ISR replacement |
| ROM | Alias for ROM_32K |
See also: Create a plain ROM.
Mapped ROM program
Note: "MegaROM" refers to a ROM of 128 KB or more. Even though they are not widely supported, there is nothing to prevent you from creating a 64 KB ROM using a mapper. We therefore prefer to use the term Mapped ROM here rather than MegaROM.
Setup
You can create program using one of the ROM mappers supported by MSXgl:
| Target | Description |
|---|---|
| ROM_ASCII8 | ASCII-8: 8 KB segments for a total of 64 KB to 2 MB |
| ROM_ASCII16 | ASCII-16: 16 KB segments for a total of 64 KB to 4 MB |
| ROM_KONAMI | Konami MegaROM (aka Konami4): 8 KB segments for a total of 64 KB to 2 MB |
| ROM_KONAMI_SCC | Konami MegaROM SCC (aka Konami5): 8 KB segments for a total of 64 KB to 2 MB |
In your build.bat, chose as target one of the above target type. You can specify the ROM size (in KB) in the ROMSize variable. Default value is 128 (KB). Any multiple value of the mapper's segment size is valid, but I recommend using powers of 2 values (64, 128, 256, etc.) to help emulators to autodetect the right mapper.
Some Build Tool configuration examples:
//-- 128 KB ASCII-8 mapped-ROM target = "ROM_ASCII8"; //-- 4 MB ASCII-16 mapped-ROM target = "ROM_ASCII16"; ROMSize = 4096; //-- 512 KB Konami SCC mapped-ROM target = "ROM_KONAMI_SCC"; ROMSize = 512;
See projects/samples/s_vgm sample for a concrete use case.
Build
Mapped-ROM use a system of sub-page (called "bank" here) the user can redirect to any segment of the ROM. Those banks are mapped to page #1 and #2 (4000h~BFFFh) of the memory space. The number of banks depends on the size of the mapper:
- 8 KB mappers have 4 banks:
- bank 0: 4000h~5FFFh
- bank 1: 6000h~7FFFh
- bank 2: 8000h~9FFFh
- bank 3: A000h~BFFFh
- 16 KB mappers have 2 banks:
- bank 0: 4000h~7FFFh
- bank 1: 8000h~BFFFh
The Build Tool build the first 32 KB of the mapped-ROM like a 32 KB plain ROM. This represents the first 4 segments for a 8 KB mapper and the first 2 for a 16 KB mapper.
The following segments are added to the ROM by the Build Tool by searching for files with a particular nomenclature: <project_name>_s<segment_number>_b<target_bank>.c.
For example with a ASCII-8 ROM of 128 KB:
program.c | Main program including segment #0~#3 (4*8 KB)
program_s4_b2.c | Segment #4 to be used in bank #2 (8000h~9FFFh)
program_s5_b3.c | Segment #5 to be used in bank #3 (A000h~BFFFh)
| No files found for segment #6 to #14: padding data added to the ROM
program_s15_b2.c | Segment #15, the last one, to be used in bank #2 (8000h~9FFFh)
Segment selection
In your program, you can then select what segment is visible from what bank using the SET_BANK_SEGMENT(bank, seg) macro. For example, to put segment 15 of the above example in bank 2, just use SET_BANK_SEGMENT(2, 15);
For information, at startup, the following segments are selected:
- 8 KB mappers:
- bank 0: segment 0
- bank 1: segment 1
- bank 2: segment 2
- bank 3: segment 3
- 16 KB mappers:
- bank 0: segment 0
- bank 1: segment 1
For more detail, see Create a mapped ROM article.
Targets overview
| Target | Selected at boot | Description | |||
|---|---|---|---|---|---|
| 0 | 1 | 2 | 3 | ||
| ROM_8K | BIOS | Cart | RAM | RAM | 8 KB ROM in page 1 (4000h ~ 5FFFh) |
| ROM_8K_P2 | BIOS | RAM | Cart | RAM | 8 KB ROM in page 2 (8000h ~ 9FFFh) |
| ROM_16K | BIOS | Cart | RAM | RAM | 16 KB ROM in page 1 (4000h ~ 7FFFh) |
| ROM_16K_P2 | BIOS | RAM | Cart | RAM | 16 KB ROM in page 2 (8000h ~ BFFFh) |
| ROM_32K | BIOS | Cart | Cart | RAM | 32 KB ROM in page 1&2 (4000h ~ BFFFh) |
| ROM_48K | BIOS | Cart | Cart | RAM | 48 KB ROM in page 0-2 (0000h ~ BFFFh) |
| ROM_48K_ISR | Cart | Cart | Cart | RAM | 48 KB ROM in page 0-2 (0000h ~ BFFFh) with ISR replacement |
| ROM_64K | BIOS | Cart | Cart | RAM | 64 KB ROM in page 0-3 (0000h ~ FFFFh) |
| ROM_64K_ISR | Cart | Cart | Cart | RAM | 64 KB ROM in page 0-3 (0000h ~ FFFFh) with ISR replacement |
| ROM_ASCII8 | BIOS | Cart | Cart | RAM | ASCII-8: 8KB segments for a total of 64 KB to 2 MB |
| ROM_ASCII16 | BIOS | Cart | Cart | RAM | ASCII-16: 16KB segments for a total of 64 KB to 4 MB |
| ROM_KONAMI | BIOS | Cart | Cart | RAM | Konami MegaROM (aka Konami4): 8 KB segments for a total of 64 KB to 2 MB |
| ROM_KONAMI_SCC | BIOS | Cart | Cart | RAM | Konami MegaROM SCC (aka Konami5): 8 KB segments for a total of 64 KB to 2 MB |
| DOS1 | RAM | RAM | RAM | RAM | MSX-DOS 1 program (starting at 0100h) |
| DOS2 | RAM | RAM | RAM | RAM | MSX-DOS 2 program (starting at 0100h) |
| DOS0 | RAM | RAM | RAM | RAM | Direct program boot from disk (starting at 0100h) |
| BIN | BIOS | BASIC | RAM | RAM | BASIC binary program (starting at 8000h) |
| BIN_USR | BIOS | BASIC | RAM | RAM | BASIC USR binary driver (starting at C000h) |
Main
For ROM or Basic program, the main function prototype is:
void main();
For DOS1 target, this prototype can also be used to get command-line arguments (set DOSParseArg to allow arguments parsing):
void main(u8 argc, const c8** argv);
For DOS2 target, this prototype can also be used to return a value du MSX-DOS:
u8 main(); u8 main(u8 argc, const c8** argv);
- argc: Integer that contains the number of arguments present in argv. The argc parameter can be 0 if no parameter have been added to the command line.
- argv: Array of null-terminated strings representing command-line arguments entered by the user of the program.
- return: The return value can be catch by MSX-DOS 2 as an error code to know if program process succeeded or not.