Organization: NETCOM On-line Communication Services (408 241-9760 guest) Path: !amdahl!amd!decwrl!sdd.hp.com!!swrinde!!!!!!sheldon The following is from a 1994 post to Usenet group by Sheldon Simms.Īrticle 1684 of : As an example of her usefulness, I have estimated that about 1K byte could be weeded out of my 5K byte Apple-II BASIC interpreter with no observable performance degradation by selectively applying
#SWEET16 PROMICRO MEASUREMENTS CODE#
Most opcodes are only one byte long, but since she runs approximately ten times slower than equivalent 6502 code, SWEET16 should be employed only when code is at a premium or execution is not. Implemented in only 300 bytes of code, SWEET16 has a very simple instruction set tailored to operations such as memory moves and stack manipulation. One of SWEET16's commands returns the user back to 6502 mode, even restoring the original register contents. Bytes stored after the subroutine call are thereafter interpreted and executed by SWEET16. The user acceses SWEET16 with a subroutine call to hexadecimal address F689. R13 stores the result of all COMPARE operations for branch testing. R0 is defined as the accumulator, R15 as the program counter, and R14 as a status register. SWEET16 contains sixteen internal 16 bit registers, actually the first 32 bytes in main memory, labelled R0 through R15. My solution to this problem of handling 16 bit data, notably pointers, with an 8 bit microprocessor was to implement a non-existent 16 bit processor in software, interpreter fashion, which I refer to as SWEET16. While writing Apple BASIC, I ran into the problem of manipulating the 16 bit pointer data and its arithmetic in an 8 bit machine. With the Sweet 16 opcodes would be one :) Nice project, extending an open-source 6502 Assembler (like CA65 from CC65) Sweet 16 enhanced 6502 source in the future. Porting Sweet 16 is easy and straightforward. Has such routines in ROM, fine, just use them. Routines to save and restore all processor registers and flags. The Apple ][ Version of Sweet 16 uses the ROM-internal "save" and "restore" Label "RTN" have to be assembled in one 6502 Page ($100/256 Bytes). Precaution have to be taken for the code. Sweet 16 uses a tricky indirect 8-Bit jump to access the routines for each Zeropage, but it have to be a contiguous range. You can place this registers anywhere in the Original Apple Version this registers are from $0 to $1F,in the ATARI Version Sweet 16 needs 32 zero page addresses for the 16 registers (R0-R15).
Registers/pointers (in zero page) and new opcodes to use this registers.Īlthough Sweet 16 is not as fast as standard 6502 code, it can reduce the code Programmer a 16 bit extension to the CPU. Sweet 16 is a kind of virtual machine that gives the 6502 Written by Apple's Steve "Woz" Wozniak and can be found in the ROM of someĪPPLE ][ Computers. Really tricky und useful extension to a 6502 computer. Sweet 16 is not a teen-magazine, nor is it a brand name for candy. Sweet 16: A Pseudo 16-bit Microprocessor.See also the appendix for material added later, after This material was provided by Carsten Strotmann, who has built a working Atari Port of Sweet 16, Programming instructions, and notes to help port it. This article includes the source code for Sweet 16, along with a brief history,
Written by Steve Wozniak and used in the Apple II, Sweet 16 can also be ported to other 6502-based systems
Sweet 16 is a metaprocessor or "pseudo microprocessor" implemented in 6502 assembly language. Porting Sweet 16 by Carsten Strotmann to Source Code Repository]
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