Hi David, > Just noticed something with the @i word with addressing. > > >> : strng s" ABCDEFGHIJKLM" ; > > ok > >> ' strng 3 + @i . > > 4241 ok > >> ' strng 4 + @i . > > 4443 ok > >> ' strng 5 + @i . > > 4645 ok > >> > > > It looks like there is an implied 'cells' when using @i. Is this correct?
The picture is a bit more complex. First the trivial things: The Atmegas use a 16bit opcode schema. Every machine instruction is basically a 16bit number. The program counter register (the pointer for the machine code) that points to the next machine instruction is incremented by 1 and points to the next flash cell, at 16bit distance. So I think its ok to assume, that the flash has 16bit per address unit, there is a 8bit access too, but that is not the "natural" size of it. EEPROM and RAM have 8bits per address unit. When I designed amforth, I wanted to keep the specific elements. Having a 16bit forth system, its obvious that I use one address unit to get the flash contents and two consecutive address units for EEPROM and RAM (Endianess is basically determined by the few 16bit ports in the IO region). They all end up in a 16bit number. Same with the addresses: a 16bit number is a perfect target for the controller PC register (aka a "far jump" instruction). Things got a little bit more complex with the 256x controllers but not that much. > (what I actually want is c@i - i.e. read 1 byte) IMHO the @i should be better named a c@i, since c@ is defined as the fetch of a single address unit content. But... Not the complex stuff: You compile strings into the flash. If you'd have written a single number, nothing complicated would have happened ;) Just look at the example code for e.g. the table driven sine function in the sources. Strings consist of many bytes for the characters (the xchar extensions from forth 2012 are not part of amforth, yet). So I decided to combine two characters into one flash cell and store them that way. That makes words like itype and find(-name) a bit more complex but the savings of flash space are more important. HTH Matthias ------------------------------------------------------------------------------ Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more! Discover the easy way to master current and previous Microsoft technologies and advance your career. Get an incredible 1,500+ hours of step-by-step tutorial videos with LearnDevNow. Subscribe today and save! http://pubads.g.doubleclick.net/gampad/clk?id=58041391&iu=/4140/ostg.clktrk _______________________________________________ Amforth-devel mailing list for http://amforth.sf.net/ Amforth-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/amforth-devel
