absolute address accessing in NIOS2

Altera_Forum · ‎12-07-2005

HI, eveyone:

i just a beginner of NIOS, i have a quetion about software development of absolute address's accessing.

for example, the system have one 1kbytes ram, its start avalon address is 0x0, and length is 0x3ff. i want to access the space which address is 0x100 in my program. can i use pointer of C language like this?

unsigned char *p=(unsigned char *)0x100;

when i want to know what's byte's data, then x=*p; when i want to give this byte's data, then *p=0xff;

how about another way to access absolute address in NIOS2 IDE? is there any document about this?

Altera_Forum · ‎12-07-2005

Hi oceanx,

if I understand what it is that you want maybe I can help you. If you want to give your data an offset en you have a base address, you should do it like this:

data = BASE_ADDRESS_OF_RAM_USED | 0x(hex-value);

this way your offset should be added with the base adress, which can be found in system.h. And data should be declared as a pointer....

Cheers,

Danny

Altera_Forum · ‎12-07-2005

Sorry didn't read it that well I think. It's still early http://forum.niosforum.com/work2/style_emoticons/<#EMO_DIR#>/tongue.gif

data = BASE_ADDRESS_OF_RAM_USED | 0x100;

Good luck,

Danny

Altera_Forum · ‎12-07-2005

Thanks, Danny

i just want to write the value-0xFF to the ram space which absolute address is 0x100. in other mcu software programming, i can do it in this way:

volatile unsigned char *p = (unsigned char *)0x100;

*p = 0xFF;

i wonder if it is the same in NIOS programming.

http://forum.niosforum.com/work2/style_emoticons/<#EMO_DIR#>/blink.gif

http://forum.niosforum.com/work2/style_emoticons/<#EMO_DIR#>/ohmy.gif

Altera_Forum · ‎12-07-2005

Hi oceanx,

did you try to do it?! Because I think that also should work... You are using the volatile statement.... In my eyes that also should work... Please let me know if it did.

Cheers,

Danny

Altera_Forum · ‎12-08-2005

Hi, Danny

Because i have no hardware board of NIOS, so i can only to simulate this program. it seems ok. my board will arrive next week, then i can try the program in the hardware.

Thanks again http://forum.niosforum.com/work2/style_emoticons/<#EMO_DIR#>/biggrin.gif

Best Regards

Yang

Altera_Forum · ‎12-12-2005

Hi oceanx,

I think that looks basically fine. However, what you might have problems with is the data cache (if you have one installed in your system) - the write might be stored there instead of written to main memory. I suggest you check the IOWR and IORD macros which are provided in HAL to bypass the cache:

Nios2 Documentation states that the 'volatile' keyword does not do the job because of a the cache machanism used in Nios2 (I believe it is called write-back cache).

<Nios II kit path>/components/altera_nios2/HAL/inc/io.h

Cheers,

-pkumpula