I recently read about the STM32V8 launch and it has pretty great specs. When you see that it has a 800 MHz on a Cortex-M with a 5,072 CoreMark, you know you are getting close to compute you normally see on embedded microprocessors(MPU) with an external DDR memory. ST positions STM32V8 as its flagship high-performance STM32 MCU.
The chip is built on 18nm FD-SOI plus embedded phase-change memory. FD-SOI is a chip process that reduces leakage current and helps push frequency without wasting as much power. It also integrates up to 4 MB of non-volatile memory and is specified up to an extreme 140°C junction temperature. The key part is the PCM.
Embedded phase-change memory (PCM) is a way to store bits without the floating gate used in Flash. The bit lives as resistance in a special material. When the material is in one phase it reads high resistance, and in the other phase it reads low resistance. Because the phase stays put when power is removed, it is non-volatile memory. You write to it by sending a short, shaped current pulse that heats the cell into the wanted phase.
This matters because embedded Flash does not scale nicely into newer chip process nodes. Resistive memories like PCM is the route most vendors take from around 28nm and below, mainly to avoid extra process complexity and cost. RRAM was another, I wrote about that one earlier in a post.
For firmware, PCM is not an infinite-write storage. The chip separates code and data profiles. Code can be around 1,000 write cycles with 10-year retention. Data can be up to 1,00,000 cycles with about 1-year retention at 140°C after cycling. This is actually great as realistically you wont have firmware changes that frequent in production. The practical benefit is you can keep more code, tables, and even small ML model weights on chip, and then buffer hot data in SRAM, the fast RAM that forgets its contents when power is off.
The new V8 chip seems to be in sampling mode currently by ST with elite customers like SpaceX because of the temp profile and radiation immunity claims.
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