mirror of https://github.com/Klaus2m5/VTL02.git
176 lines
6.3 KiB
Plaintext
176 lines
6.3 KiB
Plaintext
-----------------------------------------------------
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VTL-2 for the 6502 (VTL02C)
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Original Altair 680b version by
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Frank McCoy and Gary Shannon 1977
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2012: Adapted to the 6502 by Michael T. Barry
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see source code for copyright notice
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Thanks to sbprojects.com for a very nice assembler!
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-----------------------------------------------------
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The basic concepts of VTL-2 (Very Tiny Language):
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http://www.altair680kit.com/manuals/Altair_680-VTL-2%20Manual-05-Beta_1-Searchable.pdf
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The files:
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Original source code from Mike:
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VTL02C for the apple II & the sbprojects.com assembler
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vtl02ca2.asm
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Modified versions (Syntax, I/O & user RAM size):
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VTL02C for the Kowalski 6502 simulator
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http://www.exifpro.com/downloads/6502_1.2.12.zip
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vtl02ca2.65s
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VTL02C for my emulator & the Kingswood AS65 assembler
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vtl02ca2.a65
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VTL02C codename "Speedy Gonzales"
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vtl02sg.a65
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this is a work in progress version and is my attempt
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to trade performance versus codesize
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2015: Revision B included some space optimizations
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(suggested by dclxvi) and enhancements
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(suggested by mkl0815 and Klaus2m5):
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* Bit-wise operators & | ^ (and, or, xor)
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Example: A=$|128) Get a char and set hi-bit
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* Absolute addressed 8-bit memory load and store
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via the {< @} facility:
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Example: <=P) Point to the I/O port at P
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@=@&254^128) Clear low-bit & flip hi-bit
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* Starting with VTL02B, the space character is no
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longer a valid user variable nor a "valid" binary
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operator. It's now only significant as a numeric
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constant terminator and as a place-holder in
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strings and program listings, where it may be
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used to improve human readability (at a slight
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cost in execution speed and memory consumption).
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Example:
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* (VTL-2)
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1000 A=1) Init loop index
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1010 ?=A) Print index
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1020 ?="") Newline
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1030 A=A+1) Update index
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1040 #=A<10*1010) Loop until done
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* (VTL02B)
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1000 A = 1 ) Init loop index
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1010 ? = A ) Print index
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1020 ? = "" ) Newline
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1030 A = A + 1 ) Update index
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1040 # = A < 10 * 1010 ) Loop until done
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2015: Revision C includes further enhancements
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(suggested by Klaus2m5):
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* "THEN" and "ELSE" operators [ ]
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A[B returns 0 if A is 0, otherwise returns B.
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A]B returns B if A is 0, otherwise returns 0.
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* Some effort was made to balance interpreter code
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density with interpreter performance, while
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remaining within the 1KB constraint. Structured
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programming principles remained at low priority.
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-----------------------------------------------------
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VTL02sg for the 2m5 emulated 6502 SBC
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spaces in expressions are allowed on input but are
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removed from the stored program and listing.
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added a timer variable {/} with 10ms increments.
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the {?} input variable no longer accepts an
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expression as input. Only a number is accepted.
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added braces as shift operators.
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A}B shifts A by B bits to the right.
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A{B shifts A by B bits to the left.
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result is unpredictable if B > 16
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an expression missing the initial {=} operator
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is converted by duplicating the leftmost variable
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and inserting a {=}. {N+1} becomes {N=N+1}.
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added a statement delimiter {;} allowing multi
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statement lines.
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branch to same line is now allowed.
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{?="..."} & unmatched {)} (used for comments) can
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not be continued.
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added load and save facility to user call {>}
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"=0;>=13 loads program 13 from EEPROM
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"=1;>=42 saves current program to EEPROM as 42
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requires emulator version >= 0.83c
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line numbers >= 65280 are now reserved for the
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following fast return & goto features.
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added a gosub stack, depth = 16 address words.
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{==...} is a gosub and pushes the return address
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of the next line.
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{#==} is a return and pops the address when the
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result is the special line numer asigned to {=}.
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added a 31 line addresses acronym label array.
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lowercase characters and symbols in the $60-$7e
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range are used to address the array. the array
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is populated with the address of a line when a
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character in the allowed range preceeds the line
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number.
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example (prints the first 1000 prime numbers):
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10 /=0;Q=d;V=5;U=25;X=1000
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20 N=2;==b
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30 N+1;==b
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40 N+2;==b
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a100 N+2;==b
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120 N+4;==b
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150 #=a
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b200 #=N<U[Q;Q=c;V+2;U=V*V
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c300 D=5
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e310 A=N/D;#=%]=;D+2;#=D>V[d
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320 A=N/D;#=%]=;D+4;#=D<V[e
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d400 ?=N;?=""
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420 X=X-1;#=X[=
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435 ?="Execution time: ";
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445 ?=//100;$=46;#=%>10[465;?=0
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465 ?=%;?=" seconds"
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added message service including error messages
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runtime errors:
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233 EEPROM file corrupted
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234 EEPROM file has incompatible format
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237 EEPROM not responding
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238 EEPROM full - file not saved
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239 EEPROM file not found
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240 array pointer exceeds reserved VTL RAM
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241 user call pointer inside reserved VTL RAM
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248 duplicate label
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249 undefined label or empty return stack
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errors during program line input:
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242 invalid or missing operator
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243 invalid or missing target variable
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244 value or variable missing after operator
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245 missing closing parenthesis
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246 out of memory (*-&)
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internal changes:
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added required atomic variable fetch & store.
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replaced some jsr calls with inline code
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for skpbyte:, getbyte:, plus:, minus:.
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replaced cvbin calls to mul: & plus: with custom
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inline multiply by 10 & digit adder.
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removed simulation from startup of eval:.
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mainloop uses inline code to advance to next
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sequential program line.
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find: is now only used for true branches.
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added decimal to binary conversion on line entry
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avoiding the runtime conversion.
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abbreviated getting a simple variable in getval:.
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bypassed setting a simple variable in exec:.
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added inline divide by 10 to prnum:.
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fixed statement delimiter not overriding mismatched
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parentheses.
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merged oper: into getval: and progr: into exec:
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added a check for ctrl-c & ctrl-z during goto to
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allow user escape from a loop.
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