On 12-12-15 13:48 , Erik Christiansen wrote: > Many thanks, Johann, for the clarification that your explanation has > provided. > > On 14.12.12 23:00, Georg-Johann Lay wrote: >> The 64-bit ranges come from the ELPM instruction that takes the >> 16-bits of Z-reg and concatenates RAMPZ as bits 16..23 to get a >> 24-bit address. > > The common computer terms "paged" and "page aligned" seem to fit > perfectly here. AIUI, the Z-reg is a page register, providing base 2^16 > page addresses, and RAMPZ provides an address within the page.
It is the other way around. RAMPZ provides the higher (more significant) bits of the address (= the "page number") and Z provides the less significant bits ( = the offset from the start of the "page"). But otherwise, yes, paged addressing is similar. However, at least in some of the AVR instructions that auto-increment or auto-decrement the address, the carry/borrow extends from the 16-bit less-significant address register (Z, here) to the 8-bit, more significant register (RAMPZ, here), so the whole 24-bit address is auto-incremented/decremented. This is not common in plain paged addressing with auto-inc/dec, where the register that holds the offset in the page typically just wraps around, without affecting the page-number register, which stays put. -- Niklas Holsti Tidorum Ltd _______________________________________________ AVR-GCC-list mailing list AVR-GCC-list@nongnu.org https://lists.nongnu.org/mailman/listinfo/avr-gcc-list
