~vdupras/duskos

a98b630354747e728ec5e3bed5fb99bda7575591 — Virgil Dupras 11 months ago 60e4ee7
asm/arm: add b) bl) and bx)
3 files changed, 23 insertions(+), 6 deletions(-)

M fs/asm/arm.fs
M fs/doc/asm/arm.txt
M fs/xcomp/arm/rpi/kernel.fs
M fs/asm/arm.fs => fs/asm/arm.fs +5 -0
@@ 55,3 55,8 @@ $e5000000 const str)         $e5100000 const ldr)
: -r) ( op r -- op ) -i) $02000000 or ;
: 8b) $00400000 or ;
: !) $00200000 or ;

\ Branching
: b) ( rel32 -- op ) >> >> 2 - $ffffff and $ea000000 or ;
: bl) b) $01000000 or ;
: bx) ( r -- op ) $e12fff10 or ;

M fs/doc/asm/arm.txt => fs/doc/asm/arm.txt +17 -5
@@ 1,11 1,11 @@
# ARM assembler

ARM instructions all encode to a 32-bit number and the way these encoding work
ARM instructions all encode to a 32-bit number and the way these encodings work
incite us to deviate a little bit from the general Dusk assembler mechanism:
Instead of pushing arguments to PS and then call the "operation writer" word,
we instead begin the the operation mnemonic and "accumulate" arguments into it.
When all arguments are accumulated, the number of PS is exactly what we want to
write, which we can do with "le,", of which ",)" is an alias.
Instead of pushing arguments to PS and then call the "operation writer" word, we
begin the operation mnemonic and "accumulate" arguments into it.  When all
arguments are accumulated, the number on PS is exactly what we want to write,
which we can do with "le,", of which ",)" is an alias.

For example, to write a "add" instruction with r4 as a destination (Rd), r5 as
the first operand (Rn) and 42 as an immediate, we would do:


@@ 71,3 71,15 @@ words:
    post) op -- op    Add offset after transfer
    8b)   op -- op    Load/Store operation is 8-bit
    !)    op -- op    Write effective address back to rn)

## Branching

The b) bl) and bx) branching words differ from other mnemonic words because they
need an argument from PS. In the case of b) and bl), it's a relative offset that
follows rules described in doc/asm/intro, that is, that "0" must mean an
infinite loop.

In the case of bx), the argument is a register ID. Examples:

    begin abs>rel b) ,) \ infinite loop
    r0 bx) eq) ,) \ jump to address in R0 if Z is set

M fs/xcomp/arm/rpi/kernel.fs => fs/xcomp/arm/rpi/kernel.fs +1 -1
@@ 61,4 61,4 @@ mov) r1 rd) $300 i) ,) add) r1 rd) r1 rn) $01 i) ,)
str) r1 rd) r2 rn) UART0_CR +i) ,)

mov) r1 rd) 'X' i) ,) str) r1 rd) r2 rn) UART0_DR +i) ,)
$eafffffe , \ hardcoded "b -2"
0 b) ,)