Memory I/O Commands

Memory I/O commands have only simple, single-port access format.  Block 
I/O or indexing is not facilitated. Supported widths are Byte, Word, or 
Dword. Both destination and source represent either physical addresses or 
a register. The syntax is as follows: 

READB( destination, source );      //read from source address, store
                                             //in destination variable
READW(destination, source );
READDW( destination, source);

<destination>  ::= <register>
<source>  ::= <constant>  |  <mmio variable>

WRITEB( destination, source );          //read from source variable, store
                                        //in destination address
WRITEW( destination, source );
WRITEDW( destination, source );
<destination>  ::= <mmio variable>  |  <constant>
<source>  ::= <constant>|<register>

For example: 

writedw(interrupt_en, r1);      //interrupt_en already declared.
writeb(0xa0000080,0x88);      //write 0x88 into phys.  add 0xa00000080
readw(r1, 0xa0000080);        //read a word from 0xa0000080 into r1.