Post by Anton Ertl
PowerPC and AArch64 are closer i=
n ISA similarities (RISC, 32 GP registers, fixed length 32 bit encodings, r=
obust/fat instruction set, rigid but not too wide of SIMD units). AArch64 i=
s like a re-encoded PowerPC
Yes, when I saw the description, I got the impression that Aarch64 is
closer to PowerPC than to ARM.
which gained 5%-15% in code density and dropped=
some legacy baggage yet all of a sudden this is enough to be competitive a=
nd even have a "real advantage"?
The advantage seems to be in the business model and the current
implementation situation, not the architecture per se. It's ARMs
business to sell licenses for the architecture and for cores to
semiconductor manufacturers, and apparently the cores are good enough
for many, but weak enough that some feel the need to improve on them
(either by building from scratch, like Apple, or by improving the
existing cores). There is also an established application area in
mobile phones etc., and the server market with its focus on
performance/W looks like it is compatible with the strengths of
existing ARM implementations.
By contrast, IBM and Mot^H^HFree^H^H^H^H NXP have focused more on
making and selling implementations, and licensing to others has not
been pursued much for quite some time. Recently IBM is trying to
change this, but it's a little late. Also, IBM itself is a strong
competition in the server marketplace, and NXP in the embedded space*,
making this ecosystem not very attractive for newcomers.
* However, NXP now seems to be focussing more on ARM and considers
PowerPC legacy; there must be something in the ARM ecosystem that
makes it very attractive despite the ARM tax.
PowerPC has been popular in three areas of use. One is for processors
in workstations and Macs - that is long gone. Another is for network
processors, in high end firewalls, switches, routers, etc. That market
has always had a lot of competition from MIPS, and now ARM is taking
over. The final market is automotive microcontrollers - PPC
microcontrollers have traditionally been very solid and reliable, and
faster than most alternative cores. Again, this is shrinking.
Part of the reason for the drop in market share for PPC in embedded
systems is perception, part is due to Freescale/NXP strategy, part is
the tools, and part is the hardware. As has been noted in this thread,
PPC is not unlike AArm64 - it is big and complex. But PPC cores in the
automotive and industrial embedded world don't compete against 64-bit
ARM processors - they compete against 32-bit ARM microcontroller cores.
I have used a number of PPC based microcontroller devices over the years
- they are good devices, but they are difficult to use and complex to
work with in comparison to equally capable ARM Cortex-M or Cortex-R
devices. And for some aspects in embedded systems, such as interrupt
handling, PPC microcontrollers are terrible - and that is after getting
/much/ better in recent years. The number of people familiar with these
devices is /tiny/ in comparison to the number that are familiar with ARM
microcontrolllers. This in turn means that the tools available are
expensive and/or limited and/or old-fashioned, and the software support
of operating systems, communications stacks, etc., is far weaker than in
the ARM world.
Post by Anton Ertl
As for RISC-V, maybe the lack of the ARM tax will make it attractive,
or maybe ARM provides enough infrastructure to make paying the tax