Re:Ask HN: Have you ever regretted working on a product?
by planteen on Wednesday November 21, 2018 @02:09PM
(#18505156)
That's right, real-time does not mean real-fast. In a hard real-time system, there is a deterministic worst-case bound for response times. "Real fast" CPUs, like the latest and greatest Intel CPUs, are actually pretty difficult to get deterministic bounds on. There are factors like unpreventable SMI events, possibility of L1/L2/L3 cache misses, etc. Often systems that need to be really deterministic, like say an engine controller in a car, run on simple CPUs like the Cortex-R series from ARM.
Re:Ask HN: Have you ever regretted working on a product?
by exikyut on Thursday November 22, 2018 @10:13AM
(#18510410)
> "Real fast" CPUs, like the latest and greatest Intel CPUs, are actually pretty difficult to get deterministic bounds on. There are factors like unpreventable SMI events, possibility of L1/L2/L3 cache misses, etc.
Oh yeah. I remember reading something along the same lines about x86 a while back. I guess it didn't really go in properly, heh. Thanks
I'm reminded of the "x86 is high level" thing: https://news.ycombinator.com/item?id=9264195
Also, I think the iPhone 6's NVMe apparently uses a Cortex-R: https://ramtin-amin.fr/#nvmepcie
But again: not an RTOS expert. We had a lab that would constantly test configurations of hardware and software. And I remember them finding RTOS not being helpful.