33 Jaguar RISC cpu module

This chapter documents the backend for the Atari Jaguar GPU/DSP RISC processor.

33.1 Legal

This module is written in 2014-2017,2020,2021,2024,2025 by Frank Wille and is covered by the vasm copyright without modifications.

33.2 Additional options for this module

This module provides the following additional options:

‘-big’

Output big-endian code and data (default).

‘-little’

Output little-endian code and data.

‘-many’

Generate code for GPU or DSP RISC. All instructions are accepted (default).

‘-mdsp’

‘-mjerry’

Generate code for the DSP RISC (part of Jerry).

‘-mgpu’

‘-mtom’

Generate code for the GPU RISC (part of Tom).

‘-no-opt’

Disable all standard optimizations which do not cause any side effects.

‘-opt-jr=<n>’

Enable automatic translation of JR instructions with an out-of-range destination into MOVEI dest,Rn followed by JUMP cc,(Rn), where Rn is always the selected temporary register.

33.3 General

This backend accepts RISC instructions for the GPU or DSP in Atari’s Jaguar custom chip set according to the "Jaguar Technical Reference Manual for Tom & Jerry", Revision 8. Documentation bugs were fixed by using various sources on the net.

The target address type is 32 bits.

Default alignment for instructions is 2 bytes. Data is aligned to its natural alignment by default.

33.4 Optimizations

This backend performs the following optimizations and translations for the GPU/DSP RISC instruction set:

• - load (Rn+0),Rm is optimized to load (Rn),Rm.
• - store Rn,(Rm+0) is optimized to store Rn,(Rm).
• - movei #x,Rn is optimized to moveq #x,Rn when x is a constant from 0 to 31.
• - jr cc,label is translated to movei label,Rn plus jump cc,(Rn), when enabled by option ‘-opt-jr=<n>’.

33.5 Extensions

This backend extends the selected syntax module by the following directives (note that a leading dot is optional):

<symbol> ccdef <expression>

Allows defining a symbol for the condition codes used in jump and jr instructions. Must be constant number in the range of 0 to 31 or another condition code symbol.

ccundef <symbol>

Undefine a condition code symbol previously defined via ccdef.

dsp

Select DSP instruction set.

<symbol> equr <Rn>

Define a new symbol named <symbol> and assign the address register Rn to it. <Rn> may also be another register symbol. Note that a register symbol must be defined before it can be used.

equrundef <symbol>

Undefine a register symbol previously defined via equr.

gpu

Select GPU instruction set.

<symbol> regequ <Rn>

Equivalent to equr.

regundef <symbol>

Undefine a register symbol previously defined via regequ.

All directives may be optionally preceded by a dot (.), for compatibility with various syntax modules.

33.6 Known Problems

Some known problems of this module at the moment:

• - Encoding of MOVEI instruction in little-endian mode is unknown.
• - The developer has to provide the necessary NOP instructions after jumps, or OR instructions to work around hardware bugs, her/himself.
• - Some rare relocations are not perfectly supported. For example LOAD Rn+x or ADDQ #x,Rn, when external symbol x becomes 32.

33.7 Error Messages

This module has the following error messages:

• - 2001: data size %d not supported
• - 2002: value from %d to %d required
• - 2003: register expected