ARM9 reading the global timer register from inside a Linux application (ZYNQ)

[pogccfe]

Hello,

I need to read the global timer register of CPU1 inside a Linux application. I see that something similar is done in bare-metal applications through the headers xparameters_ps.h and xtime_l.h which read 4 bytes from address 0xF8F00200. If I were to do the same in a Lunux application:

 - Would the SCU stop me and/or do I need to do some special configuration from the Zynq processing system panel?

 - Can I just mmap to read the register or do I need to include some xilinx libraries and headers inside the PetaLinux rootfs

 - Is there something equivalen to XPAR_CPU_CORTEXA9_1_CPU_CLK_FREQ_HZ that I can refer to inside my code? (i.e. the cpu configured frequency, with cpu_freq disabled I think it is constant)

Thank you for your help!

[hpoetzl · Accepted solution]

Hey @pogccfe,

Would the SCU stop me and/or do I need to do some special configuration from the Zynq processing system panel?

let's see ...

# devmem2 0xF8F00200 w
/dev/mem opened.
Memory mapped at address 0xa6f83000.
Value at address 0xF8F00200 (0xa6f83200): 0x59E84E25

# devmem2 0xF8F00200 w
/dev/mem opened.
Memory mapped at address 0xa6f71000.
Value at address 0xF8F00200 (0xa6f71200): 0x7552AF7B

... seems to work fine.

Can I just mmap to read the register or do I need to include some xilinx libraries and headers inside the PetaLinux rootfs

You need to map the physical address to a virtual to access it.

This can, for example, be done with mmap on /dev/mem.

Hope this helps,

Herbert

[sconvertini]

Hi,

I'm using petalinux 2018.

devmem is used instead of devmem2. Do you know some differences?

If I try to execute 

devmem 0xF8F00200

the board faults and I have to reboot it.