# $NetBSD: README.models,v 1.7 2021/05/28 00:18:27 simonb Exp $

MIPS models and architecture levels
-----------------------------------

Since this is a complex and confusing topic and there's a shortage of
information (especially, a shortage of reliable information), I'm
creating this document as a reference for people doing MIPS stuff on
NetBSD (and elsewhere).

Citations appear in []. With luck all important facts have citations.


------------------------------------------------------------
1. Architecture levels.

These architecture levels exist:

       32-bit     64-bit

       MIPS-I
       MIPS-II
                  MIPS-III
                  MIPS-IV
                  MIPS-V
       MIPS32     MIPS64
       MIPS32r2   MIPS64r2
       MIPS32r3   MIPS64r3
       MIPS32r5   MIPS64r5
       MIPS32r6   MIPS64r6

Note that while MIPS32 is a 32-bit subset of MIPS64, each
corresponding pair of MIPS32rN and MIPS64rN are comparable in age and
properties. Later revisions (further down the list) are mostly supersets
of earlier revisions, although some exceptions exist.


------------------------------------------------------------
2. CPU models.

For vintage MIPS these are the standard models as of fall 1996 [idt96
A-198] and the corresponding architecture levels. (There were many
additional models put out by licensees or by the MIPS company itself,
which have model numbers with fewer zeros.)

       R2000           MIPS-I (32-bit)         [idt96 1-5]
       R3000           MIPS-I (32-bit)         [idt96 1-5]
       R4000           MIPS-III (64-bit)       [idt96 A-197]
       R4200           MIPS-III (64-bit)       [idt96 A-197]
       R4300           MIPS-III (64-bit)       [idt96 A-197]
       R4400           MIPS-III (64-bit)       [idt96 A-197]
       R4600           MIPS-III (64-bit)       [idt96 A-197]
       R5000           MIPS-IV (64-bit)        [idt96 1-5]
       R6000           MIPS-II (32-bit) with 64-bit FPU regs
       R8000           MIPS-IV (64-bit)        [idt96 1-5]
       R10000          MIPS-IV (64-bit)        [idt96 1-5]
       R1x000          MIPS-IV (64-bit)

For later models than this I currently have no information.


------------------------------------------------------------
3. CPU models present in various systems.

These are the CPU models found in various systems NetBSD does and
doesn't support. This table also notes endianness; MIPS chips are
bi-endian but are wired up one way or the other on motherboards.

  algor (little-endian [buildsh])
       Algorithmics P-4000i                    ??
       Algorithmics P-4032                     ??
       Algorithmics P-5064                     ??
       Algorithmics P-6032                     ??
  arc (little-endian [buildsh])
       Acer PICA                               ??
       MIPS Magnum 4000                        ??
       NEC Image RISCstation                   ??
       NEC Express RISCserver                  ??
       NEC RISCserver 2200                     ??
       NEC RISCstation 2200                    ??
       NEC RISCstation 2250                    ??
       NEC Express5800/230 R4400 PCI           presumably R4400 (MIPS-III)
       NEC Express5800/240 R4400 EISA          presumably R4400 (MIPS-III)
       DeskStation Tyne                        ??
  cobalt (little-endian [buildsh])
       Qube ... ??                             ??
       RaQ ... ??                              ??
  emips (big-endian [buildsh])
       ... ??                                  ??
       (see http://research.microsoft.com/en-us/projects/emips/ )
  evbmips
       Loongson 2F ( gdium, lemote etc. )      more or less LE MIPS-III with
                                               some extensions
       xburst ( as in, jz4780, found on CI20 ) LE MIPS32R2 with extensions
       ... ??                                  ?? (various-endian)
  ews4800mips (big-endian [buildsh])
       EWS4800/350                             ??
       EWS4800/350F                            ??
       EWS4800/360AD                           ??
       EWS4800/360ADII                         ??
       EWS4800/360SX                           ??
       EWS4800/360EX                           ??
       EWS4800/360                             ??
       ... ??                                  ??
  hpcmips (big-endian [buildsh])
       see http://wiki.netbsd.org/ports/hpcmips/processor_comparison/
  mipsco (big-endian [buildsh])
       Various MIPS Computer Systems, Inc.     see [mipscolist]
       Bull DPX/Prostation M-20                ??
  newsmips (big-endian [buildsh])
       NWS-3470D                               R3000 (MIPS-I) [portpage]
       NWS-3410                                R3000 (MIPS-I) [portpage]
       NWS-3460                                R3000 (MIPS-I) [portpage]
       NWS-3710                                R3000 (MIPS-I) [portpage]
       NWS-3720                                R3000 (MIPS-I) [portpage]
       NWS-3800 series                         ??
       NWS-4000 series                         R4600 (MIPS-III) [portpage]
       NWS-5000                                R4[04]00 (MIPS-III) [portpage]
  playstation2 (little-endian [buildsh])
       playstation2                            R5900
       (almost all of MIPS-III + movn/movz) [linux-mips wiki R5900]
  pmax (little-endian [buildsh])
       DECstation/system 2100 and 3100         R2000 (MIPS-I) [portpage]
       DECsystem 5100                          R3000 (MIPS-I) [portpage]
       Personal DECstation 5000/20, /25, /33   R3000 (MIPS-I) [portpage]
       Personal DECstation 5000/50             R4000 (MIPS-III) [portpage]
       DECstation/system 5000/120, /125, /133  R3000 (MIPS-I) [portpage]
       DECstation/system 5000/150              R4000 (MIPS-III) [portpage]
       DECstation/system 5000/200              R3000 (MIPS-I) [portpage]
       DECstation/system 5000/240              R3000 (MIPS-I) [portpage]
       DECstation/system 5000/260              R4400 (MIPS-III) [portpage]
       DECsystem 5900                          R3000 (MIPS-I) [portpage]
       DECsystem 5900-260                      R4400 (MIPS-III) [portpage]
       DECsystem 5500                          R3000 (MIPS-I) [portpage]
  sbmips
       BCM91250A (Swarm) evaluation board      Broadcomm BCM1250 [portpage]
  sgimips (big-endian [buildsh])
       4D/20                                   ??
       4D/25                                   ??
       Indigo                                  R3000 (MIPS-I) [portpage]
       Indigo (R4x00)                          R4?00 (MIPS-III) [portpage]
       4D/30                                   ??
       4D/35                                   ??
       Indigo2 (R4x00)                         R4?00 (MIPS-III) [portpage]
       Challenge M                             ??
       Indy (R4x00)                            R4?00 (MIPS-III) [portpage]
       Indy (R5000)                            R5000 (MIPS-IV) [portpage]
       Challenge S (R4x00)                     R4?00 (MIPS-III) [portpage]
       Challenge S (R5000)                     R5000 (MIPS-IV) [portpage]
       R10000 Power Indigo2                    R10000 (MIPS-IV) [portpage]
       Octane                                  R1x000 (MIPS-IV) [portpage]
       O2 (R5000)                              R5000 (MIPS-IV) [portpage]
       O2 (RM5200)                             RM5200 (MIPS-IV) [portpage]
       O2 (R7000)                              R7000  (MIPS-IV) [portpage]
       O2 (R10000)                             R10000 (MIPS-IV) [portpage]
       O2 (R12000)                             R12000 (MIPS-IV) [portpage]
       O2 (R14000)                             R14000 (MIPS-IV) [portpage]
       Fuel                                    R1x000 (MIPS-IV) [portpage]
       Tezro                                   R1x000 (MIPS-IV) [portpage]
       ... ??


------------------------------------------------------------
4. FPU properties

TBD... this is complex and messy (XXX / ??)


------------------------------------------------------------
5. Exception handling properties

TBD... (XXX / ??)


------------------------------------------------------------
6. MMU properties

TBD... (XXX / ??)


------------------------------------------------------------
7. Cache properties

TBD... (XXX / ??)


------------------------------------------------------------
8. Instruction ordering properties and hazards

TBD... (XXX / ??)

In the absence of the SYNC instruction before MIPS-II [idt96 A-172,
mips32insn 215], apparently on a R3000 you can force pending memory
writes to complete by doing an uncached read. [idt96 11-13]

Apparently also on some models but not others the state of the write
buffer is wired to the coprocessor 0 condition bit and you can also do
this by using the otherwise useless bc0f instruction (branch on
coprocessor 0 false) to loop. [no citation, I found this in passing
the other day with Google while looking for something else]


------------------------------------------------------------
9. Pipeline hazards

TBD... (XXX / ??)

On MIPS-I a load instruction requires an explicit one-cycle wait
before using the result. This restriction was lifted in MIPS-II,
with the addition of an interlock in the pipeline. [idt96 A-2]

A multiply should not be started within two cycles of a MFHI or MFLO
instruction, as an interrupt that requires restarting the MFHI or MFLO
might (will) get the result from the subsequent multiply. At least on
MIPS-I. [idt96 2-4]  I guess this is true for divides as well.


------------------------------------------------------------
10. Coprocessor 0 hazards

TBD... (XXX / ??)


----------------------------------------------------------------------
11. Deprecated/removed material.

When the exception handling model was changed for MIPS-III
(introducing the ERET instruction) the RFE instruction supporting the
old model was removed.  [idt96 A-134]

Coprocessor 3 (that is, the ability to have a third coprocessor, which
had never been used for anything) was removed in MIPS-III [idt96 A-197].

The branch likely instructions (e.g. BEQL) were added in MIPS-II
[mips32insn 56] and deprecated not long after, at least by MIPS32
[mips32insn 57] and were removed in release MIPS32 Release 6
[mips32newinsn2a 71].

SSNOP as a special NOP was deprecated in MIPS32/64 Release 6
[mips32newinsn2a 375] and sequences using SSNOP should include the
new EHB which counts as an SSNOP on older implementations
[mips32newinsn2a 174] ... and possibly SYNC/SYNCI ???
[mips32newinsn2a 394-401]

.. ??

------------------------------------------------------------
12. Conditional compilation in NetBSD

TBD... (XXX / ??)


------------------------------------------------------------
References:

[buildsh] The MACHINE/MACHINE_ARCH architecture table in NetBSD
       build.sh.

[idt96] "IDT MIPS Microprocessor Family Software Reference Manual",
       Integrated Device Technology, Version 2.0, dated October 1996.

[linux-mips wiki] https://www.linux-mips.org/wiki/

[mips32intro] "MIPS32(TM) Architecture For Programmers Volume I:
       Introduction to the MIPS32(TM) Architecture", MIPS
       Technologies, Document Number MD00082, Revision 0.95, dated
       March 2001. This was apparently an external review version or
       something and has been available on the Internet; the final
       version, and later revisions, never were. (AFAIK)

[mips32insn] "MIPS32(TM) Architecture For Programmers Volume II: The
       MIPS32(TM) Instruction Set", MIPS Technologies, Document Number
       MD00086, Revision 0.95, March 12, 2001. Ditto.

[mips32newinsn2a] "MIPS32(R) Architecture For Programmers Volume II-A:
       The MIPS32(R) Instruction Set Manual", Imagination, Document
       Number MD00086, Revision 6.02, dated December 10, 2014.

[mips32priv] "MIPS32(TM) Architecture For Programmers Volume III: The
       MIPS32(TM) Privileged Resource Architecture", Document Number
       MD00090, Revision 0.95, dated March 2001. Ditto.

[portpage] The port page for this NetBSD port on wiki.netbsd.org, or a
       subpage. Ideally these references should be replaced with
       something less self-referential.

[mipscolist] List of MIPS Computer Systems, Inc. machines hosted on the
       NetBSD web server: https://www.netbsd.org/ports/mipsco/models.html

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