Lpc2000

Hello,

I am using the lpc2138, and I have wrote a program which includes 
reading port0.16-24 pins at a 10 Mhz sampling rate:

                            // R6 contains port.26-24 address
LDRB R7,[R6,#0x00000002]    // R5 contains the memory address 
STRB R7,[R5,#0x00000000]!   // to store the input(auto-increments)
NOP			    // R7 is temporary storage	
LDRB R7,[R6,#0x00000002]
STRB R7,[R5,#0x00000001]!
NOP			
LDRB R7,[R6,#0x00000002]		
STRB R7,[R5,#0x00000001]! 		
NOP				
	......	
	......}    X 128 total
	......
LDRB R7,[R6,#0x00000002]		
STRB R7,[R5,#0x00000001]!		 
NOP	
LDRB R7,[R6,#0x00000002]		
STRB R7,[R5,#0x00000001]!
NOP

As you can see, it doesn't branch anywhere. The problem is:

ON THE KEIL ARM SIMULATOR (60 MHZ) THE ROUTINE SAMPLES AT 10 Mhz.

ON THE REAL CHIP (60 MHZ) THE ROUTINE SAMPLES AT 5,5 Mhz ! ( I 
specify the function to be copied to ram)	

Meanwhile, I use an output compare timer on a pin, and it works at 
10 Mhz both on the simulator and the chip (checked on a scope)!

The simulator shows the lDRB, STRB need 2,3 and the nop 1 cycle, 
hence rate = 60 / (3+2+1) = 10Mhz

I guess LDRB, STRB actually take double time. If it is so, does 
anybody know why? Is there any way around this?

I tried using four temporary registers in a chain sequence in case 
of a pipeline issue from sequentially accessing the same register, 
and stoped using write back. The result was the same. When I took 
the NOP's out, speed was increased by approx. 1/10th.

Unfortunately I must use the 2138, and it has no external bus. Is it 
possible to achieve 10 Mhz sampling with this chip?

Thank you.