While I can discern this is supposed to be gameshark v3 codes it is best to specify.
Offsets. In this context sometimes you will want data to appear at a different location to the value in the cheat itself.
This can be because it is a pointer driven value (the GBA can use C coding which means the memory does not have to be all known locations from when the devs made it as it would be for assembly*) or because the same data structure may be repeated a few times and you don't want to fiddle with slide codes. For instance if you had say 4 party members each with their own stats you might be interested in only editing say member 3 for this and could adjust the offset accordingly.
*theoretically you could dynamically allocate in assembly, or do it as an anti cheat but nobody does the former. Seen it as an anti cheat enough though.
https://doc.kodewerx.org/hacking_gba.html#ardescribe has a cleaner description
42a0aaaa xxxxyyyy 16-bit Pointer RAM Write
Writes yyyy to the address located in 0a00aaaa + xxxx * 2.
gbatek's version
42aaaaaa xxxxyyyy [ [a0aaaaa] + xxxx*2 ]=yyyy (Indirect)
The multiply by two (or indeed shifting the data as it will likely be considered by people playing in ARM code or indeed how it is likely achieved -- I believe I mentioned best to learn about shifts, rotates and such in addition to the boolean logic in a previous thread. The short version being much like the quick way of multiplying by 10 in decimal is to move the decimal place then in binary multiplying by 2 means you shift all the numbers along, dividing by 2 going the other way and reason most experience multiplier cheats in games run 2x, 4x,8x,16x,32x... ) losing a small amount of precision over not that but at the same time allowing a far larger range to be applicable.
I/O registers are how the system communicates with its peripherals -- the CPU is sitting there in space as it were (ARM don't care what it is used for, some alarm system, mobile phone, air conditioning controller, SD card.... or game console) with no particular notion of what surrounds it. Easy enough to then attach all the devices** to memory and have that be the means by which the system works.
https://problemkaputt.de/gbatek.htm#gbaiomap for a list.
Granted
Code:
04000000-040003FE I/O Registers
04000400-04FFFFFF Not used
To that end I am not sure what 04004300 is being used for -- sometimes flash carts and cheat devices colour outside the lines and do their own thing. There are also mirrors of some things but not sure if this is one (some cheat makers might use a mirror as a kind of copy protection -- you copied my cheat as nobody would do that otherwise) and sometimes there are reasons for using a mirror (the GBA cartridge itself appears in several locations in memory, while the same data will come out of it there are different wait states such that something less important won't take priority even if very little uses such things).
**in some systems the CPU or memory bus might not see everything and in fact have other methods of speaking to things like passing commands to things that are accessible, or only certain CPUs seeing things if there are multiple (the megadrive/genesis for instance having a CPU for its sound chips that only sees a fraction of the memory the main CPU sees but in turn is far more primed to deal with those sound chips than the main CPU, and we will ignore the nightmare of the Saturn. If you move up to the DS then the 3d system is kind of isolated from the main CPU with only write only commands that speak to it, and also the DS cart itself only able to be spoken to via commands rather than read from like normal memory in the case of the 99.99% of the GBA library).
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BigOnYa:
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Sicklyboy:
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K3Nv2:
