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====== Assembler for RP2040 ======

===== The idea =====

A compact Forth-style macro assembler with an efficient literal pool mechanism for the RP2040.\\
A Forth-style assembler uses all the capabilities of the Forth interpreter and assembles opcodes in between.\\
An example:
<code>
code SQUARED    ( +n -- +n^2 )
    tos tos muls,  next,
end-code
</code>
===== Implementation =====

The example code asumes a 32-bit machine that has 16-bit & 32-bit compile actions. 
It is also asumed that the code runs in RAM as noForth T on the RP2040 does.
Because the Thumb-2 opcodes of the ARMv6-M use a RISC like architecture, macros
are added to make assembly a bit more easy.
An implementation example for ''%%CODE%%'' and ''%%END-CODE%%'' is showed too. Missing words in Generic Forth are:

<code forth>
(*          ( "ccc" -- )        - Skip all text until *) is found
+TO         ( n "name" -- )     - Add n to the contents of the value "name"
VOCABULARY  ( "name" -- )       - Define a named wordlist
</code>

==== All Thumb2 instructions ====

<code forth>

✦ Two low register opcodes
    ands,       eors,       adcs,       sbcs,       rors,       tst,
    neg,        cmn,        orrs,       muls,       bics,       mvns,
    sxth,       sxtb,       uxth,       uxtb,       rev,        rev16,
    revsh,      lsls,       lsrs,       asrs,       movs,       cmp,
    
✦  Two all register opcodes
    add,        mov,        cmp,
    
✦ Three low register opcodes
    adds,       subs,       str,        strb,       strh,       ldrb,
    ldrh,       ldr,        ldrsb,      ldrsh,

✦ Two low register & 3-bits immediate
    adds,       subs,       rsbs,

✦ Two low register & 5-bits immediate
    lsls,       lsrs,       asrs,       str,        strb,       strh,   
    ldr,        ldrb,       ldrh,

✦ One low register & 7-bits immediate (RP-specific)
    add,        subs,       sub,

✦ One low register & 8-bits immediate
    movs,       cmp,        str, (rp)   ldr, (rp)   ldr,        add, (rp)
    push,       pop,        bkpt,       udf,        svc,        adr,
    stm,        ldm,        adds,       subs,

✦ Various 16-bit opcodes
    noop,       nop,        yield,      wfe,        wfi,        sev,
    cpsie,      cpsid,      bx,         blx,

✦ Fourteen jump instructions
    =?          cs?         neg?        vs?         u>?         <?
    >?          no

✦ Control structures
    if,         else,       then,       ahead,
    begin,      while,      repeat,     again,      until,
    
✦ Literal pool additions
    ALIGN,      CODE>       POOL,       APOOL,      ##

✦ Assembler macros
    ALIGN,      ##          POOL,       APOOL,      )+
    -)          NEXT,
</code>

==== Two usage examples ====

<code>
code LSHIFT ( x1 +n -- x2 )
    day tos movs,       \ 1 - +n to DAY
    tos  sp )+ ldr,     \ 2 - pop X1 to TOS
    tos day lsls,       \ 1 - Shift TOS DAY positions left
    next,               \ 6 
end-code

code KEY?)  ( -- f )
    40034018 ,          \ UART0 UARTFR 
code>
    sun  w ) ldr,       \ Read UARTFR to SUN
    tos  sp -) str,     \ Push stack
    tos  sun ) ldr,     \ Read flags
    tos 1B # lsls,      \ Build flag out of bit-4
    tos 1F # asrs,      \ Extend sign
    tos tos mvns,       \ Invert flag
    next,
end-code
</code>

<code></code>
| File name | Purpose | in Dropbox (external link) |
| [[https://www.dropbox.com/s/glvdl0runl65u3t/Thumb%20assembler%20doc%20v2.pdf?dl=1|Thumb assembler doc v2.pdf]] | Documentation | [[https://www.dropbox.com/s/glvdl0runl65u3t/Thumb%20assembler%20doc%20v2.pdf?dl=0|Assembler documentation]] |
| [[https://www.dropbox.com/s/jaw8dalna8sodut/RP2040-asm%20uni.f?dl=0|RP2040-asm uni.f]] | RP2040 assembler | [[https://www.dropbox.com/s/0ubyr344j7a1q7k/noForth-T-das.f?dl=0|noForth RP2040 assembler]] |
| [[https://www.dropbox.com/s/2g4glx7gcnmuvyl/RP2040-asm-extensions%20uni.f?dl=0|RP2040-asm-extensions uni.f]] | RP2040 ass. extensions | [[https://www.dropbox.com/scl/fi/65wbh85v95rvh4uoo5rtd/T-asm-ext.f?rlkey=v8cpj3mr45oz9ou4v3apyi5w2&dl=0|noForth assembler ext.f]] |

==== Contributions ====

<html><h2 style="background-color:yellow">Alternative Implementations</h2></html>



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