Definitions

accelerator board

Motorola 68060

The Motorola 68060 is a 32-bit microprocessor from Motorola, released in 1994, and is the successor to the Motorola 68040. The 68060 is the highest performing member of the 680x0 family.

Architecture

The 68060 (usually referred to simply as the 060, pronounced oh-sixty) is not just a redesign of the 68040, but a from-scratch entirely new processor, adding a second integer pipeline, a two cycle integer multiplication unit, a faster FPU, and branch prediction logic . It has 2 to 3 times the performance capability of the 68040 at the same clockrate . The 68060 design was led by Joe Circello.

The 68060 shares most architectural features with the original Pentium. Both have a very similar superscalar in-order dual instruction pipeline configuration, and an instruction decoder which breaks down complex instructions into simpler ones before execution. However, a significant difference is that the 68060 FPU is not pipelined and is therefore up to three times slower than the Pentium in floating point applications. In contrast to that, integer multiplications and bit shifting instructions are significantly faster on the 68060. An interesting feature of the 68060 is the ability to execute simple instructions in the address generation unit (AGU) and thereby supply the result two cycles before the ALU. Another point of interest is that large amounts of commercial compiled code were analyzed for clues as to which instructions would be the best candidates for performance optimization.

The 68060 was the last development of the 680x0 series for general purpose use, abandoned in favour of the PowerPC chips. It saw use in some late-model Amiga machines and Amiga accelerator cards as well as some Atari ST clones and a Falcon accelerator board (CT060), but Apple Inc. and the Unix world had moved onto various RISC platforms. The 68060 was introduced at 50 MHz on Motorola's 0.6 µm manufacturing process. A few years later it was shrunk to 0.42 µm and bumped to 66 MHz and 75 MHz. The 0.42 µm parts were rare, as Motorola decided to concentrate on their PowerPC RISC project. Should Motorola have decided to stick with the 680x0 series it is very likely that the next processor would have resembled Intel's P6 architecture.

Perhaps its most memorable use was in American broadcast television graphics. Chyron's Infinit!, Max!, and Maxine! series of television character generators used the 68060 as the main processor. These character generators were a fixture on many American television networks' affiliate stations.

The 68060 was also used in Nortel Meridian 1 Option 51, 61 and 81 large office PBX systems, powering the CP3 and CP4 core processor boards. A pair of these boards each sporting a 68060 could be used to make the PBX fault tolerant. This was a logical application as previous Meridian 1 cores used other Motorola chips. Nortel has since changed the architecture to use Intel processors.

Also Motorola Vanguard 6560 multiprotocol router used 50 MHz 68060 processor.

Developments of the basic core continue, intended for embedded systems. Here they are combined with a number of peripheral interfaces to reduce the overall complexity and power requirements of a design. A number of chips, each with different sets of interfaces, are sold under the name ColdFire and DragonBall.

For more information on the instruction set and architecture, see Motorola 68000.

History

The even numbers (68000, 68020, 68040, 68060) were reserved for major revisions to the 680x0 core architecture. The odd numbers (68010, 68030, 68050, 68070) were reserved for upgrades to the architecture of the previous chip (N.B. - no 68050 or 68070 was ever produced by Motorola).

For example, the Motorola 68010 (and the obscure 68012) was a 68000 with improvements to the loop instruction and the ability to suspend then continue an instruction in the event of a page fault, enabling the use of virtual memory with the appropriate MMU hardware. There were, however, no major overhauls of the core architecture. Similarly, the Motorola 68030 was a process improvement on the 68020 with the MMU and a small data cache (256 bytes) moved on-chip. The 68030 was available in speed ratings up to 50MHz.

The jump from the 68000/68010 to the 68020/68030, however, represented a major overhaul, with too many individual changes to list here.

By the time the 68060 was in production, Motorola had abandoned development of the MC680x0-based chips in favour of PowerPC.

Although the last Motorola version of the processor was the 68060, there was a 68070 processor. This device was produced by Signetics (Philips), and was a modestly improved 68000 series processor, with a simple, on-chip MMU and I²C bus support. It came out long before the 68060, and was used mostly as an embedded processor in some consumer electronics items.

Bibliography

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