floobydust wrote:
Hi Proxy,
I use a 32KB EEPROM for my C02 Pocket SBC which is addressed starting at $8000. The programmer wouldn't know where (in a memory map) that I would have it configured. So, logically, the programmer starts it at $0000, so it has an addressable range from $0000 - $7FFF. Meanwhile, the S19 record does have load address for locating the data in the EEPROM, which are in the $8000 - $FFFF range. Hence, you tell the programmer that the EEPROM has an addressable offset of $8000, so it addresses the 32KB EEPROM from $8000 - $FFFF. Hope this is clear.
oh i see, it's the same/similar problem as with a binary file then. interesting.
floobydust wrote:
Code changes.... well, as I like to say, "you can't argue with success". Filling memory... sure, the INY is quicker, but you also need to load the Y reg first, so the code may be larger, depending on register contents on entry. Not using the Y register also implies you don't disturb it's contents. It's all trade-offs. For certain routines it's advantageous to code for speed, others better to code for smaller size. For a startup routine, I generally go for smaller size as it's a one-time execute. The character input routine which is used a lot with EhBasic... you're better off optimizing for speed. Not having to set or clear the carry flag explicitly saves time as the ASL A already set it. Adding the CMP for a linefeed is just a convenience, but if your emulator used a C/R instead, it would save some additional cycles as well.
yea it's always trade-offs, it's in any programming environment.
another example, if you want a function that calculates the Sine of an 8 bit number you could either actually calculate it, or use that number as an index into an array of pre-calculated values.
floobydust wrote:
In short, there's usually multiple ways to code anything on the 6502 and the later CMOS versions with additional instructions and address modes are helpful. I tend to use the newer instructions/address modes quite a bit. I would certainly recommend putting together a small 65C02 based system at some point. My current SBC runs at 6MHz, although I have one SCC2691 that survives an 8MHz clock. My next SBC will use a newer NXP DUART and will hopefully run beyond 14MHz.
As always, enjoy the project and learn from everything you do.
having a SBC is pretty cool, mine can run at 16MHz perfectly fine. though the ROM size is rather small at 8kB. i do have an expansion port so i could add more ROM via that...
but currently i just want to get the 65C02 for Digital done so i got the Verilog code for it. and afterwards i want to look into FPGAs so i can either use my simualted CPU or finally build a simple VGA graphics card for my SBC... (and overall for anyone who wants a cheap VGA Card for their 65C02 based system)
either way i got a lot of fun projects ahead and i hope you have too!
Login
Register
FAQ
Search
