Editor's note - Ingar is also responding to a question I
8-bit MCUs in a recent edition of the Focus on MCU newsletter: "What
are your thoughts on 8-bit versus 16-bit versus 32-bit MCUs?"
Why is everybody talking about the CPU? In our experience,
microcontrollers are chosen by their feature set and if they meet the
application requirements, not by the width of the CPU instruction. The
basic question is: Does the MCU have the correct peripheral set for the
application? Does it meet cost and power constraints?
Part of the drive to 32-bit CPUs can be explained by the fact that
applications need more peripherals. Processing peripherals requires
interrupts, each of which requires many MIPS to service. In many
instances, the computational load can be met easily by an 8-bit CPU.
The extra MIPS are required for interrupt processing, not computation.
C-friendly, RISC 8-bit CPUs, like the AVR, solve the shortcomings of
traditional 8-bit CPUs with a linear address space, single-cycle
instructions, a 32-byte register file where all registers acts as
accumulators. AVR XMEGA solves the interrupt issue by off-loading
peripheral-to-peripheral communications to an event manager with DMA.
It literally eliminates interrupts altogether, improving response times
and cutting power consumption.
I have still not seen a market analysis that has a larger 32-bit than
8-bit microcontroller market in its forecast. 32-bits are the fastest
growing, but 8-bit still enjoy more than 40% market share and will
continue to do so in the foreseeable future. This is measuring in
dollar revenue shipped. Looking at units shipped, 8-bit market share is
If given a choice, I think many designers would prefer to stick with
their 8-bit devices, as long as they can get the peripheral set and
performance they need. The success and fast growth of the AVR product
line is strong evidence that 8-bit MCUs are not going to be replaced
any time soon.
David Patterson, known for his pioneering research that led to RAID, clusters and more, is part of a team at UC Berkeley that recently made its RISC-V processor architecture an open source hardware offering. We talk with Patterson and one of his colleagues behind the effort about the opportunities they see, what new kinds of designs they hope to enable and what it means for today’s commercial processor giants such as Intel, ARM and Imagination Technologies.