Lpc2000

--- In lpc2100@yahoogroups.com, Ben Dooks <ben@f...> wrote:
> On Wed, Dec 03, 2003 at 10:44:28AM -0000, Leon Heller wrote:
> > I'm using the following code for software direct digital waveform
synthesis:
> > 
> > int main(void)
> > {
> >   unsigned int i;
> >   unsigned long int acc, adder;
> >   unsigned int ptr, temp;
> > 
> >   initPLL();
> >   MAMCR = 0;
> >   MAMTIM = 5;
> >   MAMCR = 2;
> >   VPBDIV = 0x01;
> >   portInit();
> >   //main loop
> >   //add value to accumulator
> >   //load byte from current table
> >   //output byte to port
> >   //repeat
> > 
> >   adder = 2000;               //set up adder
> >   acc = 0;                    //clear accumulator
> >   while (1)
> >   {
> >     acc = acc + adder;      //update phase accumulator
> >     ptr = (acc &= 0xFF);    //pointer into table
> >     IOSET = square[ptr] << 8;//output byte to port
> >     IOCLR = ~(square[ptr] << 8);
> >   }
> >   return 0;
> > }
> > 
> > but I can't get an equal mark-space ratio out of it for a square
wave, and
> > sine waves are completely screwed up.
> 
> what is the compiler outputing for this code? do you have a disassembly
> of the code being produced?
>

Thanks for the suggestion.

This is what I'm getting:

    while (1)
40000150 E3A0024E mov r0, #0xe0000004
40000154 E280090A add r0, r0, #0x28000
40000158 E59F1028 ldr r1, [pc, #40]
4000015C E3A022CE mov r2, #0xe000000c
40000160 E282290A add r2, r2, #0x28000
    {
      acc = acc + adder;      //update phase accumulator
40000164 E084400C add r4, r4, r12
      ptr = (acc &= 0xFF);    //pointer into table
40000168 E20440FF and r4, r4, #0xff
      IOSET = square[ptr] << 8;//output byte to port
4000016C E7D43001 ldrb r3, [r4, r1]
40000170 E1A03403 mov r3, r3, lsl #0x8
40000174 E5803000 str r3, [r0, #0]
      IOCLR = ~(square[ptr] << 8);
40000178 E7D43001 ldrb r3, [r4, r1]
4000017C E1E03403 mvn r3, r3, lsl #0x8
40000180 E5823000 str r3, [r2, #0]
40000184 EAFFFFF6 b -10 ; 0x40000164
40000188 4000062C andmi r0, r0, r12, lsr #0xc
    }

I'm not all that familiar with ARM assembler, but it looks about
right.  I'm using the Rowley tools, which use the GNU compiler.

Leon