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author | Shinji KONO <kono@ie.u-ryukyu.ac.jp> |
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date | Sat, 04 May 2019 11:17:42 +0900 |

parents | 2088fd998865 |

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BASIC AND FLOATING POINT ROUTINES FOR THE 6809 ============================================== sbc09 stands for Lennart Benschop 6809 Single Board Computer. It contains a assembler and simulator for the Motorola M6809 processor. copyleft (c) 1994-2014 by the sbc09 team, see AUTHORS for more details. license: GNU General Public License version 2, see LICENSE for more details. FLOATING POINT ROUTINES FOR THE 6809 ------------------------------------ They are intended to be used with the sbc09 system. These routines should be fairly portable to any 6809-based system. As it is an unfinished program (intended to become a full-featured BASIC interpreter one day), I never released it before and I almost forgot about it. Fortunately it was still on a backup CD-R that I made in 2001. FILES - - - makeflot.c Conversion tool to convert floatnum.src to floatnum.inc floatnum.inc Floating point constants to be included in main program. floatnum.src Same constants, but not converted to binary. fbasic.asm RPN calculator with floating point (just to test the FP routines. This was intended to be part of a larger Basic interpreter, but this was never finished). basic.asm Tiny Basic basic.txt Tiny Basic instructions It was originally planned to turn this into a full-fledged BASIC interpreter (maybe somewhat like BBC Basic), but this never happened. It is now a rudimentary RPN calculator, just to test the floating point routines. Each number or command needs to be on a separate line. MAKE THE PROGRAMS - - - - - - - - - Simple: make Or in single steps: compile the helper tool ... ./makeflot <floatnum.src >floatnum.inc assemble the FP calculator ... ./a09 fbasic.asm assemble Tiny Basic (integer only) ... ./a09 basic.asm RUN THE PROGRAMS - - - - - - - - Start the board simulator ../v09 You should see the prompt "Welcome to BUGGY version 1.0" Type the command xl400 Press the escape character Control-] (e.g. on Linux for a german style keyboard Control+AltGr+9) Then you see the v09> prompt. Type the command ufbasic Now the file "fbasic" will be uploaded to the board. Type the command g400 Now you can type floating point numbers and commands (RPN style), each on a different line, like this 2 3 * 6.00000000E+00 1 0 / The last calculation breaks back to the monitor. The following commands are available (see the source): + - * / (the normal arithmetic operators). = compare top two numbers on stack (and leave them), show < = or > i round to integer (round to -Inf, like BASIC INT() function). q square root s sin c cos t tan a atan l ln e exp d duplicate number on stack x exchange top numbers on stack. r remove top of stack. IMPLEMENTATION NOTES - - - - - - - - - - This is a 40-bit float, like many microcomputers of the 80s had, including the Commodore 64, the ZX-Spectrum, the BBC and others. It has an 8-bit exponent and a 32-bit mantissa (with hidden leading bit). The basic operations (including square root) should be as accurate as can be expected. It does not do IEEE-754 features, such as Infinity, NaN, +/-zero and subnormal numbers, but appears to work quite reasonably. Trig functions deviate a few places in the 9th decimal. In particular sin(pi/2) shows as 9.99999998E-01 instead of 1.00000000E+00. I consider this acceptable and consistent with what could be expected. The Log function deviates a few places in the 8th decimal. LN(5) appears to be about worst-case. I find this a bit disappointing. 2 l 5 l + e should show exactly 10, but it shows 9.99999970E+00 instead. This is not caused by the exp function, but by the log of 5 (as I checked with Python).