| ??? 02/22/11 09:24 Read: times |
#181236 - ARM core already tiny enough that you gain no more Responding to: ???'s previous message |
Oliver Sedlacek said:
Device cost is mostly proportional to silicon area, and the ARM devices probably do well because they use a comparatively advanced technology which results in a small die area. The NRE costs of a die shrink on a mature 8 bitter will probably never be recouped, and will therefore never happen. The die size isn't really affected by the size of the core, i.e. 8-bit or 32-bit. A ARM7EJ-S core in 0.13u is 0.45mm2 large. But the actual wafer size needs to be much larger, since the chip needs peripherials and most importantly it needs bonding pads and huge I/O transistors. The bonding pads and I/O transistors takes up a very significant percentage of the wafer size for a 0.13u microcontroller. That means that a number of thousand transistors more or less in the core doesn't actually matter. And you can't shrink the core any further and get any gain from getting smaller die sizes. That is why 32-bit ARM processors are so tough competitors to 16-bit and 8-bit processors. But the other important view, is that a generally low-tech core like the 8051 can be produced with very low-tech production equipment. So it is cheap to build a fab to make them. Because of improvements in technology, even smaller companies can afford fab capacity - or even afford building own fabs. When the 8051 got introduced, the fab cost was high. But today, universities can easily afford own production equipment that manages to build 8051 chips - and software to design new variants. That is a huge reason why it is hard to make real profits from the low-end 8051 chips. NXP can't produce them cheaper than anyone else. And countries with lower salaries do have great advantages on their side. So while the ARM chips have a denser core in a more advanced technology, that technology doesn't give them a real gain in production cost. Instead, the manufacturers needs to kill of a lot of 8051 competition and use the more high-tech production technology to add in more peripherial functions. At 0.13 u, an extra UART and a matrix multiplexer to route the signals takes way less die space than what it would do for a 8051 designed in "classic" technologies. So what we end up with from the major manufacturers are 8051 chips that do use new technology and draws hardly any current at all, or runs at very high speeds. Or cheap ARM chips with large amounts of peripherial extras. |
