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| -rw-r--r-- | usr.bin/pcc/arch/nova/README | 122 |
1 files changed, 0 insertions, 122 deletions
diff --git a/usr.bin/pcc/arch/nova/README b/usr.bin/pcc/arch/nova/README deleted file mode 100644 index e5d1078947e..00000000000 --- a/usr.bin/pcc/arch/nova/README +++ /dev/null @@ -1,122 +0,0 @@ -$OpenBSD: README,v 1.2 2007/09/15 22:04:38 ray Exp $ - -Calling conventions, stack frame and zero page: - -The variables that normally are placed on the stack or in registers in C -are instead allocated in the zero page and saved on a (fictive) stack -when calling functions. Some locations have predefined functions though. -Arrays allocated as automatics are stored on the stack with a pointer -in zero page to its destination. - -0-7 Unused -10 Stack pointer -11 Frame pointer -12-14 Unused -15 Used by prolog -16 Prolog address, written in crt0 -17 Epilog address, written in crt0 -20-27 Auto-increment, scratch -30-37 Auto-decrement, scratch -40-47 Unused -50-57 Scratch/Arguments -60-77 Permanent, save before use. -100-377 Addresses for subroutines, written by the assembler - -The normal registers (AC0-AC3) are all considered scratch registers. - -Register classes are assigned as: - AC0-AC3: AREGs. - AC2-AC3: BREGs. - 50-77: CREGs. - ...and eventually register pairs as DREGs. - -In byte code the low half of a word is the first byte (little-endian). -This is bit 8-15 in Nova syntax. - -The stack is growing towards lower adresses (as opposed to the Eclipse stack). -Stack layout: - - ! arg1 ! - ! arg0 ! - fp -> ! old pc! - ! old fp! - pc -> ! saved ! - -A reference to a struct member in assembler, a = b->c; b is in ZP 50 -+ is zeropage-addressing -* is fp-adressing - -# offset 0 -+ lda 0,@50 # load value from indirect ZP 50 into ac0 -* lda 2,,3 # load value from (ac3) into ac2 -* lda 0,,2 # load value from (ac2) into ac0 - -# offset 12 -+ lda 2,50 # load value from ZP 50 into ac2 -+ lda 0,12,2 # load value from (ac2+12) into ac0 -* lda 2,,3 # load value from (ac3) into ac2 -* lda 0,12,2 # load value from 12(ac2) into ac0 - -# offset 517 -+ lda 2,50 # load value from ZP 50 into ac2 -+ lda 0,.L42-.,1 # load offset from .L42 PC-indexed -+ addz 0,2,skp # add offset to ac2 and skip -+.L42: .word 517 # offset value -+ lda 0,,2 # load value from (ac2) into ac0 - -The prolog/epilog implementation; it is implemented as subroutines. - -.L42: .word 13 # number of words to save -func: - sta 3,@40 # save return address on stack - lda 2,.L42-.,1 # get save word count - jsr @45 # go to prolog - ... - lda 2,.L42-.,1 # get restore word count - jmp @46 # jump to epilog - -# words to save in 2, return address in 3 -prolog: - sta 2,45 # save # of words to move at scratch - lda 0,41 # get old fp - lda 1,40 # get sp - sta 1,41 # save new fp - dsz 40 # decrement stack, will never be 0 - sta 0,@40 # save old fp - dsz 40 - - lda 0,off57 # fetch address of regs to save - 1 - sta 0,20 # store address at autoincr -1: lda 0,@20 # get word to copy - sta 0,@40 # push on stack - dsz 40 # manually decrement sp - dsz 45 # copied all words? - jmp 1b,1 # no, continue - jmp 0,3 # return - -epilog: - sta 2,45 # save # of words to move at scratch - - lda 3,off57 # fetch address of regs to save - sta 3,20 # store at autoincr - lda 3,41 # fetch fp - sta 3,30 # store at autodecr - lda 3,@30 # get old fp - -1: lda 2,@30 # fetch word from stack - sta 2,@20 # store at orig place - dsz 45 # enough? - jmp 1b,1 # no, continue - - lda 2,41 # get new fp - sta 2,40 # restore stack - sta 3,41 # restore old fp - jmp @40 # Return - -Assembler syntax and functions. - -The assembler syntax mimics the DG assembler. -Load and store to addresses is written "lda 0,foo" to load from address foo. -If foo is not in zero page then the assembler will put the lda in the -text area close to the instruction and do an indirect pc-relative load. - |