REP #$30

LDX #$0000

.LoopStart
LDA #$0000
STA $7FC800,x
LDA #$2525
STA $7FC800,x

INX
INX
CPX #$3800
BCC .LoopStart

SEP #$30

2180 rwb++++ WMDATA - WRAM Data read/write
xxxxxxxx

This register reads to or writes from the WRAM address set in $2181-3.
The address is then incremented. The effect of mixed reads and writes
is unknown, but it is suspected that they are handled logically.

Note that attempting a DMA from WRAM to this register will not work,
WRAM will not be written. Attempting a DMA from this register to
WRAM will similarly not work, the value written is (initially) the Open
Bus value. In either case, the address in $2181-3 is not incremented.


2181 wl++++ WMADDL - WRAM Address low byte
2182 wm++++ WMADDM - WRAM Address middle byte
2183 wh++++ WMADDH - WRAM Address high bit
-------x xxxxxxxx xxxxxxxx

This is the address that will be read or written by accesses to $2180.
Note that WRAM is also mapped in the SNES memory space from $7E:0000 to
$7F:FFFF, and from $0000 to $1FFF in banks $00 through $3F and $80
through $BF.

Verious docs indicate that these registers may be read as well as
written. However, they are wrong. These registers are open bus.

DMA from WRAM to these registers has no effect. Otherwise, however, DMA
writes them as normal. This means you could use DMA mode 4 to $2180 and
a table in ROM to write any sequence of RAM addresses.

The value does not wrap at page boundaries on increment.

int CountBits (unsigned int x )
{
static unsigned int mask[] = { 0x55555555,
0x33333333,
0x0F0F0F0F,
0x00FF00FF,
0x0000FFFF
} ;

int i ;
int shift ; /* Number of positions to shift to right*/
for ( i =0, shift =1; i < 5; i ++, shift *= 2)
x = (x & mask[i ])+ ( ( x >> shift) & mask[i]);
return x;
}