Wrong Timeout Value with ARM A9 private timer.

Hello,

I am starting a bare-metal development on DE0-Nano-SoC_Computer.

I use the development tool: DS5 AE.

I begin by a timer program found in the document “DE0-Nano-SoC Computer System with ARM Cortex-A9”:

equ bit_24_pattern, 0x01000000

/* this program provides a simple example of code for the arm a9. it:

* 1. starts the arm a9 private timer

* 2. loops forever, toggling the hps green light ledg when the timer expires

*/

.text

.global _start

_start:

ldr r0, =0xff709000 // gpio1 base address

ldr r1, =0xfffec600 // mpcore private timer base address

ldr r2, =bit_24_pattern // value to turn on the hps green light ledg

str r2, [r0,# 0x4] // write to the data direction register to set

// bit 24 (ledg) of gpio1 to be an output

ldr r3, =200000000 // timeout = 1/(200 mhz) x 200×10∧6 = 1 sec

str r3, [r1] // write to timer load register

mov r3,# 0b011 // set bits: mode = 1 (auto), enable = 1

str r3, [r1,# 0x8] // write to timer control register

loop:

str r2, [r0] // turn on/off ledg

wait: ldr r3, [r1,# 0xc] // read timer status

cmp r3,# 0

beq wait // wait for timer to expire

str r3, [r1,# 0xc] // reset timer flag bit

eor r2, r2,# bit_24_pattern // toggle ledg value

b loop

.end

The timeout is not 1 sec but about 40 sec. the good value is 5 000 000 instead of 200 000 000.

Is it necessary to initialize the system clocks before launching the program?

Thanks for your help.

Jerome