Struct interface for IO doesn't work

Hi Jordan,

> However, every time I read from a memory address through the old struct interface of NIOS I,

> the compiler uses a ldw assembly instruction.

This is correct behavior.

> If I do the same memory-mapped read using the macros supplied with NIOS II, the compiler

> uses a ldwio.

If you're referring to the IORD/WR macros, this is correct.

> What gives?

The compiler doesn't know anything about your data cache. If you don't implement a data

cache, then ldw/ldwio behave identically. However, if you do implement a data cache you

need to do one of two things:

1. Use the IO macros, which will explicitly use ldxio, or,

2. Make your structs (describing registers) volatile, and use -mno-cache-volatile.

The volatile keyword in no sufficient -- it only tells the compiler that it must perform

memory read/write on each object reference (rather than storing it in a register). But it

doesn't tell the compiler anything about _how_ to access the object -- that's where the

compiler flag comes in :-)

Hope this helps.

Regards,

--Scott