[Oberon] Unexplained operation code

[Chris Burrows]

> -----Original Message-----
> From: Oberon [mailto:oberon-bounces at lists.inf.ethz.ch] On Behalf Of
> Walter Gallegos
> Sent: Thursday, 20 September 2018 10:29 PM
> To: ETH Oberon and related systems; Walter Gallegos
> Subject: [Oberon] Unexplained operation code
> 
> I'm finding the source of an unexplained operation code generated for
> debug my VHDL sources, cleaning unrelated code I wrote :
> 
> MODULE*  TestA;
>      IMPORT SYSTEM;
> 
>      VAR
>          a: INTEGER;
> 
>        PROCEDURE* IntServ;
>        BEGIN
>        END IntServ;
> 
> BEGIN
>      a := SYSTEM.ADR(IntServ);
> END TestA.
> 
> 
> a := SYSTEM.ADR(IntServ); is generated as :
> 
> 19    F7000000    BL    0
> 20    40F90030    SUB    R0    LNK    48
> 21    A0D00000    STR    R0    SB    0
> 
> I can't explain the line 19.
> 

It is the (sneaky) RISC5 way of obtaining the value of PC. BL 0 stores the
value of PC+1 in the LNK register (R15) and then just branches to the next
instruction.

Regards,
Chris

Chris Burrows
CFB Software
http://www.astrobe.com/RISC5