Fw: Labels/branching in assembler macros

Kevin,

with IF THEN and BEGIN UNTIL you do not need any labels & forward
references.
please see working example:

CODE CHFL \ a --- f, check 128kby block if erased, f=0 erased

S )+ A0 MOV D2 CLR 8000 # D0 MOV \ 32768 * 4 = 131072 bytes

                 BEGIN

A0 )+ D1 MOV FFFFFFFF # D1 EOR
0= NOT IF ( not erased) 1 # D2 MOV 1 # D0 MOV THEN

1 #Q D0 SUB 0= UNTIL

D2 S -) MOV

RTS END-CODE

----- Original Message -----
From: "Bulgrien, Kevin" <Kevin.Bulgrien_at_GDSATCOM.com>
To: <swiftx_at_forth.com>
Sent: Thursday, 05 October, 2006 11:08
Subject: [swiftx] Labels/branching in assembler macros

> I am interested in learning a good way to use labels and forward
references
> to labels in ASSEMBLER macros or CODE/END-CODE blocks using FORTH style so
I
> do not have to manually calculate the PC offset. Is this possible, and
does
> anyone care to offer a bit of insight that might help me accumulate a
> modicum
> of FORTHish understanding to store up for the future encounters with
> assembly
> language in this environment? The context in which this question occurs
is
> shown in following paragraphs.
>
> A recent debug effort put me face to face with the SwiftX assembler as I
> needed to do some debug in an interrupt handler. The TMS320C3X DSP has
> a pipeline too, so I wanted the code to be fast by inlining code instead
> of calling it, and I wanted to avoid causing pipeline conflicts due to
> branching. It did appear that using forward references was faster,
> smaller, and simpler, but being a FORTH novice and a FORTH assembler
> initiate, I did not know how to handle labels in the FORTH assembler.
> Take the following assembly pseudo-code:
>
> COMPARE_INSTRUCTION
> Label DEFERRED_BRANCH_INSTRUCTION
> INSTRUCTION
> INSTRUCTION
> INSTRUCTION
> CONDITIONAL_INSTRUCTIONS
> Label: BRANCH_DESTINATION
> MORE_CODE
>
> A fellow developer had to remind me that IF ELSE THEN and the other code
> block words work in assembler, so I looked at them but understandably they
> were not implemented with deferred branches. Unfortunately I did not look
> deeper, but left to my own devices, and using asm.f as an example, I came
> up with code to create an instruction-relative branch "mnemonic" such that
> BLTD --> BLTDR for BLTD Relative that allowed a deferred branch to be
> written like the following where BLTDR is a variation on BLTD:
>
> COMPARE_INSTRUCTION
> 1 # BLTDR
> INSTRUCTION
> INSTRUCTION
> INSTRUCTION
> CONDITIONAL_INSTRUCTION
> BRANCH_DESTINATION
> MORE_CODE
>
> I asked another peer about it and learned that the following does the same
> thing without making any special mnemonics, so the above has gone in the
> trash bin and has been chalked up as a learning experience.
>
> COMPARE_INSTRUCTION
> BEGIN 1+ BLTD
> INSTRUCTION
> INSTRUCTION
> INSTRUCTION
> CONDITIONAL_INSTRUCTION
> BRANCH_DESTINATION
> MORE_CODE
>
> --
> Kevin R. Bulgrien
> Design and Development Engineer
>
>
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Received on Thu Oct 05 2006 - 14:34:36 PDT