Forum Discussion

Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
19 years ago

wrong flash allocation

In my SOPC builder, I set the ext_flash address from 0x00000000 to 0x00FFFFFF. However, after booting, the FLASH is allocated in 0x80000000 - 0x810000000.(shown as below) Is there anyone meeting...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
19 years ago

Hi weichuan,

the mapping of flash from 0x0 to 0x80000000 isn't necessarily an error.

The Nios2 processor uses the most significant address bit as cache bypass.

If bit 31 is set, the Nios2 bypasses the data cache and accesses memory directly.

Perhaps Redboot sets this bit to avoid cache troubles with flash.

Cache bypass is explained in the "Nios II Software Developers Handbook", Chapter 7, heading "Managing Cache in Multi-Master Systems".

Bye,

Wolfgang