I\O Speed Problem

First of all NXP recommends to operate the device to a max of 72 MHZ !

This devices have support for both legacy(slow) I/O and Fast GPIO .What are you using ?

With Fast GPIO an I/O access should take 2 cycles only. So given the addresses of I/O are set you can achieve the required speed.

Suvidh

Use VPBDIV = 0x01

Hi Suvidh,

I have also tried to run my LPC2364 at 72MHz but still I am not getting 16MHz. I tried the maximum speed that it can work upto. I could go upto 75MHz max. After that my LPC2364 stoped working.

As per you have written i should get
72MHz/4 Cycles(2 cycle for on + 2 cycles for off)=18MHz
but i am not getting it?

I am using a realview Keil IDE 3.03a. My code is as under

while(1)
{ FIO2PINL=0x0001; FIO2PINL=0x0002; FIO2PINL=0x0003; FIO2PINL=0x0004; FIO2PINL=0x0005; FIO2PINL=0x0006; FIO2PINL=0x0007; FIO2PINL=0x0008; FIO2PINL=0x0009; FIO2PINL=0x000A; FIO2PINL=0x000B; FIO2PINL=0x000C; FIO2PINL=0x000D;
.... and the sequence follows
}

In this way i should get I\O at 18MHz at P2.0
But i am getting only 13MHz.

Is it the problem of my compiler?? Should i go to assembly or thumb mode to reduce time??

i have also tried with the statements in assembly as

__asm (mov FIO2PINL,0x0001)

it gives the same output.

Can you figure out the problem?? Please help it is argent.

Hi Viktor,

What is VPBDIV. I searched for the same in the usermanual of lpc2364. This register is not present in my lpc.

Can you give me the details about which lpc u r refering to and what is the use of the statement.

Actualy VPBDIV is for LPC21xx. Sorry for that. Check bit PPCLKSEL1[3:2] for LPC23xx. When set as 01you get PCLK = CCLK . With default value (00) you get PCLK = CCLK/4

The ideal speed of 18MHz will be for something like this

LDR R0,=FIO2PIN0
MOV R1,#0x01
MOV R2,#0x02

STRB R1,[R0]
STRB R2,[R0]
STRB R1,[R0]
STRB R2,[R0]
....

ANY data loading instructions in between the STRB will reduce the speed (say a mov instruction - 1 cycle which will be required in your case) will reduce the speed.

If your requirement is only that a limited sequence output should be fast, then you can hold the data in registers (say R1-R10)and store it to the IO in succession.

Suvidh

Hi Suvidh,

Thank you for the explanation. I have to increment the same from 0 to 1024(decimal). and i can not have that many registers. Even if i use the increment then it will waste one cyle.

I have got a way for it. i am using counters for the same. i am using commands

FIOPINSET=0x01;
FIOPINCLR=0x01;

this usis the same method that u have written. 0x01 is stored in a register and it gives me 18MHz pulses. I am generating the rest from giving this signal to a counter.

Thank you for the replies.