TNYCALC -

By David (Z80DAD) Collins in 2023

Thanks to Pierre Sarrazin for assistance with adding mc6839 direct linking
supprt to CMOC, and for assistance with the Makefile.

Thanks to Tim Lindner for his excellent mc6839 wrapper - this code was
instrumental in getting linker support into CMOC in the first place.

This is a small RPN calculator program for the coco and the assist09 machine
language monitor.

I built a "slowmath.h" library in C to support some trig functions. since mc6839
has floating point arithmetic, comparison and BCD conversion but not much in
the way of trig functions (which are supported by math.h on most modern c
compilers)

ISSUES:

LOG PERFORMANCE IS VERY SLOW ON THE COCO -- this uses 160 passes through a
Taylor series -- very slow, also math is computed 8-16 bits at a time
(depending on the operation)

I did try to use CORDIC but the limitations of both FLOAT and rounding
performance of the MC6839 Floating Point mask ROM made accuracy an issue.

at this point the LOG functions would need to be re-written in asembly, or
limit the digits past the decimal point to a less than useful amount (maybe
the 100ths place) under a 63C09 clocked at 5Mhz E (20Mhz external clock) it's
decent for a calculator -- most-likely not good enough for games. would need
machine language and a better algorithm (possibly look-ups -- look-ups =
memory, we are already using 8k for the mask-rom.)

one idea would be to copy the LOG algorithm from GWBASIC (since it is open
source) -- at some point I want to look into this to see if the code is at all
difficult to back port to the 6x09 from its 8086 real mode code. If it's
basically the same algorithm from Extended Color basic, we might be able to
use the disassembled source code to come up with a sort of "clean room - open
source safe" math.h of sorts. The lack of 32bit maths are a huge issue to
getting floating point code into an 8 bit cpu. its also possible that the
undocumented 63C09 accumulator could be utilized -- however given the
additional clock cycles to utilize it it may be a wash compared to just simply
slogging through the computations in traditional 6809 code -- which would be
more portable.

COMPILING:

on a properly installed cmoc install with access to make for coco:

make

on a properly installed comc install with access for assist09:

make TARGET=Ast09

manually compile something like (for coco):

cmoc --mc6839 tnycalc-coco.c floatstack.c cocoio.c slowmath.c

or

cmoc --mc6809 --void-target tnycalc-ast09.c ast09.c floatstack.c slowmath.c

RUNNING:

"RUN" the .bin file in xroar under coco machine type. This uses the coco.h
header so it will not work on the dragon.

I also included a .srec for loading into Jeff Tranters modified Motorola
Assist09 asembly language monitor. any SBC running that firmware should work.

load the srec in Assist09

L <enter>

{paste srec to terminal}

once loaded

G 0 <enter>


DIRECTIONS:

RPN Computes left to right. This is the top two operands on the stack, with
the bottom one representing the operation on the left.

example

10 <enter>
2 <enter>
+ <enter>

will change the top of the stack to 12

for more complex problems
3(2+3)

3 <enter>
2 <enter>
3 <enter>
+ <enter>
* <enter>

top of the stack will equal 15

Single operand operators (trig functions)

enter a number, enter

type '!' then the corresponding function

10 <enter>
!L <enter> (LOG10)

should return 1.

below is the output help screen when typing "&?"

THE STACK HAS THE SPACE OF 8 OPERANDS,
OVERFLOW WILL CAUSE A STACK RESET.

TWO OPERAND ARITHMETIC OPERATORS:
 + <- ADD
 - <- SUBTRACT
 * <- MULTIPLY
 / <- DIVISION

SINGLE OPERAND OPERATORS:(ASSUMES RADIANS)
 - !R -> SQUARE THE TOP OF THE STACK
 - !S -> SINE THE TOP OF THE STACK
 - !C -> COSINE THE TOP OF THE STACK
 - !T -> TANGENT THE TOP OF THE STACK
 - !L -> COMPUTE LOG10 OF THE TOP OF THE STACK
 - !N -> COMPUTE NATURAL LOG OF THE TOP OF THE STACK

NON OPERAND OPERATORS:
 - &D -> DISPLAY THE STACK
 - &I -> INITIALIZE THE STACK (AC BUTTON)
 - &Q -> QUIT
 - &? -> THIS SCREEN