Why are the IO registers stored redundantly?

spacy51 · Post by **spacy51** » Mon Aug 17, 2009 4:20 pm

In Globals.cpp, there is "u8 *ioMem = 0;", which should contain all the IO registers, but all the IO registers are declared again seperately in the same file.

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I can see that whenever a register has to be changed, it looks like this:

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DISPCNT = (value & 0xFFF7);
UPDATE_REG(0x00, DISPCNT);

You can replace DISPCNT by any other register. Keep in mind 0x00 is the IO register's offset from 0x04000000 (the IO registers adress in GBA's memory map).

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Here's the definition for UPDATE_REG:

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#define UPDATE_REG(address, value)\
 {\
   WRITE16LE(((u16 *)&ioMem[address]),value);\
 }\

It writes the value to ioMem, certainly a redundancy.

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Why is it done like that?

Couldn't we delete all the single registers and only use ioMem?

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Proposal:

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#define DISPCNT  ioMem[0x0000]
#define DISPSTAT ioMem[0x0004]
...