Bios?

Hel · May 1st, 2006

What's the BIOS for?

I somehow know how it functions for PCs but how do it function for VBA?

pokemonhacker_ · May 1st, 2006

The bios, wich is inside a chip of the GBA, holds functions that are specific to the GBA, like data decompression, memory copy, math functions... The games use some special opcodes, called software interrupts (swi), that can directly jump to the bios and execute a function. It has some advantages : the programmers don't have to write down their own functions, as they are provided by the bios ; these routines are launched from the bios area, in which code is executed faster than inside the rom area ; and they have been optimized and are known to work correctly (so the programmers don't need to 'debug' them).
Almost all the bios functions are emulated by VBA, by its 'internal bios', so in theory, a bios file isn't needed to emulate the GBA correctly. However, there are two slight difference between the emulated bios and the real bios : the duration of the bios functions aren't the same (if you use a bios file, the functions will be emulated 'perfectly', and their execution will (should) take the same amount of time that they take on the real hardware ; but if you use the emulated bios, the function's duration will either be equal to 0, or will be different from the original ones). And this duration difference can create some problems for a very small number of games that highly rely on timings (actually I only heard of one game having a problem : madden '06). Also, some swi that are used for sound aren't emulated for some (copyright) reasons, so some (few) games won't have sound when played with the emulated bios of VBA.

Hel · May 2nd, 2006

why do some games freeze when BIOS is activated on VBA then?

games like Riviera or DemiKids.

**Spacy** · May 2nd, 2006

@PokémonHacker
"some swi that are used for sound aren't emulated for some (copyright) reasons"

May you explain me the details regarding those copyright problems? Does the GBA use DOlby Digital or soemthing like that? xD

pokemonhacker_ · May 2nd, 2006

Actually I don't remember 100% why they are not emulated, that's why I put the word copyright in parenthesis (I somewhat remember it had something to do with a table of data, so copying it would bring up a copyright problem, but I might be wrong, it could be for another reason...).

@hel maybe because you are using a bad bios (debug, or a corrupted one) ?

**Forgotten** · May 2nd, 2006

Just post the data from the Help->Bug Report on VBA and we can tell whether you have a good or bad BIOS file (not much more than can be done by us). Either way, you can always try to run with VBA's internal BIOS instead and see if it works. There are a few games that do require the real good bios in order to work.

As for why the sound routines are not emulated, is because it is not easy. The sound function is big. Anyone with time and patience could write a C version of it, I just didn't think it was worth the time.

Sigilstun · May 27th, 2006

Quote:

Originally Posted by Forgotten

Just post the data from the Help->Bug Report on VBA and we can tell whether you have a good or bad BIOS file (not much more than can be done by us).

Hope you don't mind if I take you up on that bios check offer

Here's my bug report:

Emu version : 1.8.0-beta 3
Emu Type : Normal Version
Using BIOS : 1
Skip BIOS : 0
Disable SFX : 0
Skip intro : 0
Throttle : 0
Rewind : 0
Auto frame : 0
Video option : 7
Render type : 1
Color depth : 32
Red shift : 00000013
Green shift : 0000000b
Blue shift : 00000003
Layer setting: FF00
Mirroring : 0
Save type : 0 (0)
Flash size : 00010000 (00010000)
RTC : 0 (0)
AGBPrint : 0
Speed toggle : 0
Synchronize : 1
Sound OFF : 0
Channels : 030f
Old Sync : 0
Priority : 2
Filters : 12 (0)
Cheats : 0
GB Cheats : 0
GB Emu Type : 1

Thanks in advance!

May 1st, 2006	#1 (permalink)
Hel Registered User Join Date: Feb 2006 Location: Village of the Wind Deity, Philippines Posts: 50	Bios? What's the BIOS for? I somehow know how it functions for PCs but how do it function for VBA? __________________ ~to hel with you~ credits to ineedfire

May 2nd, 2006	#3 (permalink)
Hel Registered User Join Date: Feb 2006 Location: Village of the Wind Deity, Philippines Posts: 50	why do some games freeze when BIOS is activated on VBA then? games like Riviera or DemiKids. __________________ ~to hel with you~ credits to ineedfire

May 2nd, 2006	#4 (permalink)
Spacy Emu author Join Date: Mar 2005 Location: Germany Posts: 368	@PokémonHacker "some swi that are used for sound aren't emulated for some (copyright) reasons" May you explain me the details regarding those copyright problems? Does the GBA use DOlby Digital or soemthing like that? xD __________________ Windows XP Home SP3 Intel C2D E8200 4GB DDR2-800 GeForce 8800 GT ASUS Xonar DX KNC ONE TV-Station DVB-S Technisat SkyStar HD (DVB-S2) 2x Samsung HD501LJ (RAID-0)

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May 1st, 2006	#2 (permalink)
pokemonhacker_ Registered User Join Date: Jun 2005 Location: France Posts: 50	The bios, wich is inside a chip of the GBA, holds functions that are specific to the GBA, like data decompression, memory copy, math functions... The games use some special opcodes, called software interrupts (swi), that can directly jump to the bios and execute a function. It has some advantages : the programmers don't have to write down their own functions, as they are provided by the bios ; these routines are launched from the bios area, in which code is executed faster than inside the rom area ; and they have been optimized and are known to work correctly (so the programmers don't need to 'debug' them). Almost all the bios functions are emulated by VBA, by its 'internal bios', so in theory, a bios file isn't needed to emulate the GBA correctly. However, there are two slight difference between the emulated bios and the real bios : the duration of the bios functions aren't the same (if you use a bios file, the functions will be emulated 'perfectly', and their execution will (should) take the same amount of time that they take on the real hardware ; but if you use the emulated bios, the function's duration will either be equal to 0, or will be different from the original ones). And this duration difference can create some problems for a very small number of games that highly rely on timings (actually I only heard of one game having a problem : madden '06). Also, some swi that are used for sound aren't emulated for some (copyright) reasons, so some (few) games won't have sound when played with the emulated bios of VBA.

May 2nd, 2006	#5 (permalink)
pokemonhacker_ Registered User Join Date: Jun 2005 Location: France Posts: 50	Actually I don't remember 100% why they are not emulated, that's why I put the word copyright in parenthesis (I somewhat remember it had something to do with a table of data, so copying it would bring up a copyright problem, but I might be wrong, it could be for another reason...). @hel maybe because you are using a bad bios (debug, or a corrupted one) ?

May 2nd, 2006	#6 (permalink)
Forgotten Emu author Join Date: Oct 2001 Posts: 483	Just post the data from the Help->Bug Report on VBA and we can tell whether you have a good or bad BIOS file (not much more than can be done by us). Either way, you can always try to run with VBA's internal BIOS instead and see if it works. There are a few games that do require the real good bios in order to work. As for why the sound routines are not emulated, is because it is not easy. The sound function is big. Anyone with time and patience could write a C version of it, I just didn't think it was worth the time.