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Microprocessor:

Microprocessors in terms of this web site are broken down into two broad categories. There are soft core microprocessors (Microblaze) and the hard core embedded microprocessor (PowerPC). Here is the difference:

We have made probably the best FPGA on the planet. It is called the Virtex2Pro. Many of the various models of this device have embedded IBM PowerPC 405 processors embedded into them. You don't have to use them but you can't remove them. They are in the fabric of the chip.

The rest of our FPGA family (Virtex, Spartan2, VirtexE, etc.) felt jealous. They wanted their own processor so we created Microblaze. It is a virtual processor that is created out of bits of code. You only use as much of the processor as you desire. This makes it very efficient to develop onto the chip. EDK is the development tool for both processors. First let's talk a little more about Microbaze.

The Microblaze is a virtual microprocessor that is built by combining blocks of code called cores. The beauty to this approach is that you only end up with as much microprocessor as you need. You can also tailor the project to your specific needs (IE: flash, UART, GPIO, etc.).

Microblaze is an embedded soft core that includes the following features:

• Thirty-two 32-bit general purpose registers.
• 32 bit instruction word with three operands and two addressing modes.
• Separate 32-bit instruction and data buses that conform to IBM's OPB (On-chip Peripheral Bus) specification.
• 32-bit address bus
• Single issue pipeline

The MicroBlaze pipeline is a parallel pipeline, divided into three stages:Fetch, Decode, and Execute.

In general, each stage takes one clock cycle to complete. Consequently, it takes three clock cycles (ignoring delays or stalls) for the instruction to complete. Each stage is active on each clock cycle so three instructions can be executed simultaneously, one at each of the three pipeline stages.

According to the Xcell Journal, "the MicroBlaze 32-bit soft processor is the industry's fastest soft processing solution. It runs at 150 MHz and delivers 100 D-MIPS. It features a RISC archecture with Harvard-style, separate 32-bit instruction and data buses running at full speed to execute programs and access data from both on-chip and external memory. A standard set of peripherals is IBM CoreConnect bus- enabled to offer MicroBlaze designers compatibility and reuse.

Fig 1. A view on a Microblaze sistem

In contrast, PowerPC 405 processor embedded in the Virtex2Pro FPGA includes the following features:

• 5- stage data path pipeline
• 16Kb Data (D) and Instruction (I) Caches
• Embedded Memory Management Unit
• Execution Unit:
  • Multiply/divide unit
  • 32x32-bit GPR
• Dedicated on-chip memory interfaces
• Timers: PIT, FIT, Watchdog
• Debug and trace support
• Performance around 450 DMIPS @ 300 MHz.
• 0.9mW/MHz typical power consumption.

Fig 2. A simple view on a PPC system

alnz | UNM - XUP