Hi,
I'm using a Nios to access off-chip memories via the SoPC-builer's external memory bridge. The Nios is 32-bit data, the memories are
16-bit data. Using SignalTap I can see that Nios is only accessing even addresses in the external memory (using germs monitor commands and/or my own c-code). Has anyone there come across something like this before? Thanks in advance,Alan Myler
Hi Alan:
A classic situation. The CPU references each byte (8 bits) in memory using address bit 0. But the CPU accesses memory in 2 byte chunks (16 bits) so the CPU only needs to output even addresses. If the program accesses a byte of data from memory, the CPU reads the 16 bits (even address) containing that byte and the data bus interface directs either the high byte or the low byte into the low 8 bits on the CPU input bus.
If you had a 32 bit wide memory bus the CPU would only read addresses divisible by 4 and then direct one of the 4 bytes appropiately.
gm
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