Hi Kövesdi, > Is there any possibility to tell the compiler such a dependency? Are those variables which map to hardware registers indicated as such (e.g., volatile), so the compiler is informed that they cannot be subject to certain optimizations? When I worked on code that had memory mapped I/O registers, I had take special care in the code to mark the variable which referenced that memory mapped I/O location as volatile. Since one memory mapped I/O register spanned 4 bytes, I also had to take extra-special care to make sure reading/writing 1 byte did not befoul the other 4 bytes (since the architecture had a 32-bit data bus, and could not read/write 1 byte on the bus at a time ... the GCC compiler would generate not-so-helpful muxing code to shift and mask for me, otherwise). But I did not have inter-dependent volatiles, such as "set a byte in memory mapped I/O port X, and then set a byte in memory mapped I/O port Y to 'send' the byte in X". Is that (more or less) your situation? HTH, --Eljay
