amiga-bootcamp/15_cpu_and_mmu/68040_68060_libraries.md

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68040.library and 68060.library — CPU Support Libraries

Overview

The 68040 and 68060 processors removed certain instructions that the 68020/68030 supported in hardware. These "unimplemented" instructions cause a Line-F exception when executed. The 68040.library and 68060.library are trap handler libraries that catch these exceptions and emulate the missing instructions in software, providing transparent backward compatibility.

Without these libraries, any program using the affected instructions would crash with a Line-F exception on 040/060 hardware.

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What Instructions Are Emulated?

68040.library

The 68040 removed several FPU instructions that the 68881/68882 supported:

Category	Missing Instructions	Description
Transcendental FPU	FSIN, FCOS, FTAN, FASIN, FACOS, FATAN	Trig functions
Transcendental FPU	FSINH, FCOSH, FTANH, FATANH	Hyperbolic functions
Transcendental FPU	FLOG2, FLOG10, FLOGN, FLOGNP1	Logarithms
Transcendental FPU	FETOX, FETOXM1, FTWOTOX, FTENTOX	Exponentials
Other FPU	FMOD, FREM	Modulo/remainder
Other FPU	FGETEXP, FGETMAN	Get exponent/mantissa
Other FPU	FSGLDIV, FSGLMUL	Single-precision ops
Integer	MOVEP	Move peripheral (not on all 040 revisions)

68060.library

The 68060 removed everything the 040 removed plus additional instructions:

Category	Additionally Missing	Description
Integer	MOVEP	Move peripheral (byte-strided)
Integer	CAS2	Compare-and-swap dual
Integer	CHK2, CMP2	Range check
Integer	MULU.L (64-bit)	64-bit unsigned multiply
Integer	MULS.L (64-bit)	64-bit signed multiply
Integer	DIVU.L (64-bit)	64-bit unsigned divide
Integer	DIVS.L (64-bit)	64-bit signed divide
FPU	All 68040-missing FPU ops	Same as above
FPU	FMOVECR	Move constant ROM
FPU	FDABS, FDSQRT, etc.	Some double-precision ops

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How They Work

1. Program executes FSIN (opcode $F200 xxxx)
2. 68040/060 CPU has no microcode for this → Line-F exception (#11)
3. CPU vectors to the Line-F exception handler
4. 68040.library's handler decodes the opcode from the stack frame
5. Software emulates FSIN using basic FADD/FMUL/FDIV
6. Result is placed in the correct FPU register
7. Handler returns → program continues as if nothing happened

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Installation

These libraries are loaded at boot time as resident modules. They install themselves as the Line-F exception vector handler.

; In startup-sequence or user-startup:
LIBS:68040.library    ; for 68040 systems
; or:
LIBS:68060.library    ; for 68060 systems (replaces 68040.library)

The library is typically loaded by SetPatch or an explicit C:LoadModule:

C:LoadModule LIBS:68040.library
; or for 68060:
C:LoadModule LIBS:68060.library

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struct (ROM Tag)

Both libraries register as RTF_COLDSTART resident modules with high priority to ensure they are initialised before any user code runs:

/* Typical RomTag for 68040.library: */
static struct Resident romtag = {
    RTC_MATCHWORD,         /* $4AFC */
    &romtag,
    &endskip,
    RTF_COLDSTART,         /* flags: cold start */
    40,                    /* version */
    NT_LIBRARY,
    105,                   /* priority: very high */
    "68040.library",
    "68040.library 40.1 (1.1.93)\r\n",
    initRoutine
};

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Detection

/* Check which CPU is present: */
if (SysBase->AttnFlags & AFF_68040)  /* 68040 */
if (SysBase->AttnFlags & AFF_68060)  /* 68060 */

/* AttnFlags bits: */
#define AFB_68010   0
#define AFB_68020   1
#define AFB_68030   2
#define AFB_68040   3
#define AFB_68060   7   /* added by 68060.library */
#define AFB_68881   4   /* FPU present */
#define AFB_68882   5
#define AFB_FPU40   6   /* 040 internal FPU */

---

Performance Impact

Software emulation of transcendental FPU instructions is 10–100x slower than the 68881/68882 hardware implementation. Performance-critical code should:

• Use lookup tables for trig functions
• Use polynomial approximations (Chebyshev, CORDIC)
• Avoid FSIN/FCOS in tight loops

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Common Sources

Library	Source
68040.library 37.4	Commodore (OS 3.0 distribution)
68040.library 40.1	Commodore (OS 3.1 distribution)
68060.library 40.1	Phase5 (original 68060 accelerators)
68060.library 46.x	Motorola reference implementation

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References

• Motorola: MC68040 User's Manual — unimplemented instruction list
• Motorola: MC68060 User's Manual — unimplemented instruction list
• NDK39: exec/execbase.h — AttnFlags
• Phase5: 68060.library source (public domain)