The Cortex-M0+ processor
supports a new I/O interface which allows single cycle accesses and so
enables faster I/O port operations. The processor’s I/O interface is a
generic 32-bit interface to which microcontroller vendors then add their
own I/O port peripherals. With this I/O interface, the Cortex-M0+
processor can perform peripheral accesses faster than any of the popular
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the I/O interface is part of the system’s memory map, the I/O register
on this interface can be accessed with normal pointers in C and does not
require specific C language extension features such as special data
Because accesses to the AMBA® AHB-Lite™ and the single
cycle I/O interface can be made concurrently, the Cortex-M0+ processor
can fetch the next instructions while accessing the I/Os. This enables
single cycle I/O accesses to be sustained for as long as needed.
applications will also benefit from this improvement, by either running
at lower speed for the same I/O toggling frequency, or by completing
the I/O control more quickly, then going faster into a sleep mode.
Cortex-M0+ processor also includes many useful features from the
Cortex-M3 and Cortex-M4 processors previously not available in the
Cortex-M0 processor. For example, it supports privileged and
unprivileged execution levels, and a Memory Protection Unit (MPU), which
is similar to that in the Cortex- M3 and Cortex-M4 processors. The MPU
is a programmable component with 8 programmable regions, and can be used
by an OS to create access permission rules for various application
tasks dynamically during run time. By using this mechanism, the design
can prevent an application task from corrupting memory space used by
other tasks and the OS kernel.
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.