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339 lines
9.2 KiB
Forth
339 lines
9.2 KiB
Forth
( Configuration words: RAMSTART, RS_ADDR )
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H@ 256 /MOD 2 PC! 2 PC!
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( RESERVED REGISTERS
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At all times, IX points to RSP TOS and IY is IP. SP points
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to PSP TOS, but you can still use the stack in native code.
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you just have to make sure you've restored it before "next".
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)
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( STABLE ABI
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Those jumps below are supposed to stay at these offsets,
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always. If they change bootstrap binaries have to be
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adjusted because they rely on them. Those entries are
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referenced directly by their offset in Forth code with a
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comment indicating what that number refers to.
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)
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H@ ORG !
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0 JPnn, ( 00, main )
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0 JPnn, ( 03, find )
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NOP, NOP, ( 06, unused )
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NOP, NOP, ( 08, LATEST )
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NOP, ( 0a, unused )
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0 JPnn, ( 0b, cellWord )
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0 JPnn, ( 0e, compiledWord )
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0 JPnn, ( 11, pushRS )
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0 JPnn, ( 14, popRS )
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EXDEHL, JP(HL), NOP, ( 17, nativeWord )
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0 JPnn, ( 1a, next )
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0 JPnn, ( 1d, chkPS )
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NOP, NOP, ( 20, numberWord )
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NOP, NOP, ( 22, litWord )
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NOP, NOP, ( 24, addrWord )
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NOP, NOP, ( 26, unused )
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RAMSTART 0x4e + JPnn, ( 28, RST 28 )
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0 JPnn, ( 2b, doesWord )
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NOP, NOP, ( 2e, unused )
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RAMSTART 0x4e + JPnn, ( RST 30 )
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0 JPnn, ( 33, execute )
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NOP, NOP, ( unused )
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RAMSTART 0x4e + JPnn, ( RST 38 )
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( BOOT DICT
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There are only 3 words in the boot dict, but these words'
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offset need to be stable, so they're part of the "stable
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ABI"
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)
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'E' A, 'X' A, 'I' A, 'T' A,
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0 A,, ( prev )
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4 A,
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H@ XCURRENT ! ( set current tip of dict, 0x42 )
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0x17 A, ( nativeWord )
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0x14 CALLnn, ( popRS )
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HL PUSHqq, IY POPqq, ( --> IP )
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JPNEXT,
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CODE (br) ( 0x53 )
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L2 BSET ( used in CBR )
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E 0 IY+ LDrIXY,
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D 1 IY+ LDrIXY,
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DE ADDIYss,
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JPNEXT,
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CODE (?br) ( 0x67 )
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HL POPqq,
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chkPS,
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A H LDrr,
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L ORr,
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JRZ, L2 BWR ( BR + 2. False, branch )
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( True, skip next 2 bytes and don't branch )
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IY INCss,
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IY INCss,
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JPNEXT,
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( END OF STABLE ABI )
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( We want numberWord and litWord routine to be below the 0x100
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offset so that we can reduce the size of the routine field
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in words to 1 byte. )
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( addrWord is the exact same thing as a numberWord except that
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it is treated differently by meta-tools. See notes.txt )
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PC ORG @ 0x20 + ! ( numberWord )
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PC ORG @ 0x24 + ! ( addrWord )
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( This is not a word, but a number literal. This works a bit
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differently than others: PF means nothing and the actual
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number is placed next to the numberWord reference in the
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compiled word list. What we need to do to fetch that number
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is to play with the IP.
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)
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E 0 IY+ LDrIXY,
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D 1 IY+ LDrIXY,
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IY INCss,
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IY INCss,
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DE PUSHqq,
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JPNEXT,
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PC ORG @ 0x22 + ! ( litWord )
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( Similarly to numberWord, this is not a real word, but a
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string literal. Instead of being followed by a 2 bytes
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number, it's followed by a null-terminated string. When
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called, puts the string's address on PS )
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IY PUSHqq, HL POPqq, ( <-- IP )
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HL PUSHqq,
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( skip to null char )
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A XORr, ( look for null )
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B A LDrr,
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C A LDrr,
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CPIR,
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( CPIR advances HL regardless of comparison, so goes one
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char after NULL. This is good, because that's what we
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want... )
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HL PUSHqq, IY POPqq, ( --> IP )
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JPNEXT,
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( Name of BOOT word )
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L1 BSET
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'B' A, 'O' A, 'O' A, 'T' A, 0 A,
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PC ORG @ 1 + ! ( main )
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( STACK OVERFLOW PROTECTION:
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To avoid having to check for stack underflow after each pop
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operation (which can end up being prohibitive in terms of
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costs), we give ourselves a nice 6 bytes buffer. 6 bytes
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because we seldom have words requiring more than 3 items
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from the stack. Then, at each "exit" call we check for
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stack underflow.
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)
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SP 0xfffa LDddnn,
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RAMSTART SP LD(nn)dd, ( RAM+00 == INITIAL_SP )
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IX RS_ADDR LDddnn,
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( HERE begins at RAMEND )
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HL RAMSTART 0x80 + LDddnn,
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RAMSTART 0x04 + LD(nn)HL, ( RAM+04 == HERE )
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( LATEST is a label to the latest entry of the dict. It is
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written at offset 0x08 by the process or person building
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Forth. )
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0x08 LDHL(nn),
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RAMSTART 0x02 + LD(nn)HL, ( RAM+02 == CURRENT )
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EXDEHL,
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HL L1 @ LDddnn,
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0x03 CALLnn, ( 03 == find )
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0x33 JPnn, ( 33 == execute )
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PC ORG @ 4 + ! ( find )
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( Find the entry corresponding to word name where (HL) points
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to in dictionary having its tip at DE and sets DE to point
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to that entry. Z if found, NZ if not.
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)
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BC PUSHqq,
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HL PUSHqq,
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( First, figure out string len )
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BC 0 LDddnn,
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A XORr,
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CPIR,
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( C has our length, negative, -1 )
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A C LDrr,
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NEG,
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A DECr,
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( special case. zero len? we never find anything. )
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JRZ, L1 FWR ( fail )
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C A LDrr, ( C holds our length )
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( Let's do something weird: We'll hold HL by the *tail*.
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Because of our dict structure and because we know our
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lengths, it's easier to compare starting from the end.
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Currently, after CPIR, HL points to char after null. Let's
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adjust. Because the compare loop pre-decrements, instead
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of DECing HL twice, we DEC it once. )
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HL DECss,
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BEGIN, ( inner )
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( DE is a wordref, first step, do our len correspond? )
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HL PUSHqq, ( --> lvl 1 )
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DE PUSHqq, ( --> lvl 2 )
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DE DECss,
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LDA(DE),
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0x7f ANDn, ( remove IMMEDIATE flag )
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C CPr,
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JRNZ, L2 FWR ( loopend )
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( match, let's compare the string then )
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DE DECss, ( Skip prev field. One less because we )
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DE DECss, ( pre-decrement )
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B C LDrr, ( loop C times )
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BEGIN, ( loop )
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( pre-decrement for easier Z matching )
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DE DECss,
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HL DECss,
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LDA(DE),
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(HL) CPr,
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JRNZ, L3 FWR ( loopend )
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DJNZ, AGAIN, ( loop )
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L2 FSET L3 FSET ( loopend )
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( At this point, Z is set if we have a match. In all cases,
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we want to pop HL and DE )
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DE POPqq, ( <-- lvl 2 )
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HL POPqq, ( <-- lvl 1 )
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JRZ, L2 FWR ( end, match? we're done! )
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( no match, go to prev and continue )
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HL PUSHqq, ( --> lvl 1 )
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DE DECss,
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DE DECss,
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DE DECss, ( prev field )
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DE PUSHqq, ( --> lvl 2 )
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EXDEHL,
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E (HL) LDrr,
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HL INCss,
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D (HL) LDrr,
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( DE conains prev offset )
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HL POPqq, ( <-- lvl 2 )
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( HL is prev field's addr. Is offset zero? )
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A D LDrr,
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E ORr,
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IFNZ, ( noprev )
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( get absolute addr from offset )
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( carry cleared from "or e" )
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DE SBCHLss,
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EXDEHL, ( result in DE )
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THEN, ( noprev )
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HL POPqq, ( <-- lvl 1 )
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JRNZ, AGAIN, ( inner, try to match again )
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( Z set? end of dict, unset Z )
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L1 FSET ( fail )
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A XORr,
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A INCr,
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L2 FSET ( end )
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HL POPqq,
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BC POPqq,
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RET,
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PC ORG @ 0x12 + ! ( pushRS )
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IX INCss,
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IX INCss,
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0 IX+ L LDIXYr,
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1 IX+ H LDIXYr,
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RET,
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PC ORG @ 0x15 + ! ( popRS )
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L 0 IX+ LDrIXY,
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H 1 IX+ LDrIXY,
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IX DECss,
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IX DECss,
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RET,
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'(' A, 'u' A, 'f' A, 'l' A, 'w' A, ')' A, 0 A,
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L1 BSET ( abortUnderflow )
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HL PC 7 - LDddnn,
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DE RAMSTART 0x02 + LDdd(nn), ( RAM+02 == CURRENT )
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0x03 CALLnn, ( find )
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0x33 JPnn, ( 33 == execute )
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PC ORG @ 0x1e + ! ( chkPS )
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HL PUSHqq,
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RAMSTART LDHL(nn), ( RAM+00 == INITIAL_SP )
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( We have the return address for this very call on the stack
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and protected registers. Let's compensate )
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HL DECss,
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HL DECss,
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HL DECss,
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HL DECss,
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SP SUBHLss,
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HL POPqq,
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CNC RETcc, ( INITIAL_SP >= SP? good )
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JR, L1 BWR ( abortUnderflow )
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L2 BSET ( chkRS )
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IX PUSHqq, HL POPqq,
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DE RS_ADDR LDddnn,
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DE SUBHLss,
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CNC RETcc, ( IX >= RS_ADDR? good )
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JR, L1 BWR ( abortUnderflow )
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PC ORG @ 0x1b + ! ( next )
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( This routine is jumped to at the end of every word. In it,
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we jump to current IP, but we also take care of increasing
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it by 2 before jumping. )
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( Before we continue: are stacks within bounds? )
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0x1d CALLnn, ( chkPS )
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L2 @ CALLnn, ( chkRS )
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E 0 IY+ LDrIXY,
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D 1 IY+ LDrIXY,
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IY INCss,
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IY INCss,
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( continue to execute )
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PC ORG @ 0x34 + ! ( execute )
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( DE points to wordref )
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EXDEHL,
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E (HL) LDrr,
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D 0 LDrn,
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EXDEHL,
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( HL points to code pointer )
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DE INCss,
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( DE points to PFA )
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JP(HL),
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PC ORG @ 0x0f + ! ( compiledWord )
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( Execute a list of atoms, which always end with EXIT.
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DE points to that list. What do we do:
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1. Push current IP to RS
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2. Set new IP to the second atom of the list
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3. Execute the first atom of the list. )
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IY PUSHqq, HL POPqq, ( <-- IP )
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0x11 CALLnn, ( 11 == pushRS )
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EXDEHL, ( HL points to PFA )
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( While we increase, dereference into DE for execute call
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later. )
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E (HL) LDrr,
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HL INCss,
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D (HL) LDrr,
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HL INCss,
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HL PUSHqq, IY POPqq, ( --> IP )
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0x33 JPnn, ( 33 == execute )
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PC ORG @ 0x0c + ! ( cellWord )
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( Pushes PFA directly )
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DE PUSHqq,
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JPNEXT,
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PC ORG @ 0x2c + ! ( doesWord )
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( The word was spawned from a definition word that has a
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DOES>. PFA+2 (right after the actual cell) is a link to the
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slot right after that DOES>. Therefore, what we need to do
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push the cell addr like a regular cell, then follow the
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linkfrom the PFA, and then continue as a regular
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compiledWord.
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)
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DE PUSHqq, ( like a regular cell )
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EXDEHL,
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HL INCss,
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HL INCss,
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E (HL) LDrr,
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HL INCss,
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D (HL) LDrr,
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0x0e JPnn, ( 0e == compiledWord )
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