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There os an in between space like the RPi zero where you can drop rt linux kernel (and rt modules). 32bit embedded linux is still really quite widespread. I exp

There os an in between space like the RPi zero where you can drop rt linux kernel (and rt modules). 32bit embedded linux is still really quite widespread. I expect risc-v to breath some new life into it as well. Sometimes a lack of hard (or any) real time requirements, combines with price and occasionally power (where I expect risc-v to come in) to allow for embedded linux. It usually requires less development time too. Think how many home routers, and security systems are still built off of 32bit linux. I don't know any built off of freebsd though, so maybe a good call?

yjftsjthsd-h 3y ago
Actually I've been surprised at how much 64-bit dominates RISC-V even in the very lowest end of Linux-capable embedded. Perhaps I'm just in a bubble, though; not like I work in actual embedded stuff professionally.
adrian_b 3y ago
The price difference between something with Cortex-A55 64-bit cores and something with obsolete 32-bit cores is negligible. For modern home routers or security appliances you want them to be able to easily execute firewalls with complex sets of rules at multi-gigabit per second throughput, so that the router throughput should not be limited by the CPU instead of the Ethernet or WiFi interfaces. For this, you really need something like Cortex-A55. The routers with obsolete CPUs limit the performance without any worthwhile price reduction. On the other hand, for many embedded projects where a 32-bit CPU is the right choice, the developers choose Linux just because they are familiar with it and they are too lazy to read the manuals of some free real-time operating system, even if in fact the latter might require less development work and maintenance work for their software project.
- pantalaimon 3y ago
  The more bits you have to push around / the wider your registers and busses are, the more energy you are going to consume though.
  - zokier 3y ago
    Is that actually measurable difference on modern process nodes and cores as big as Cortex-A?
- zokier 3y ago
  If even A55 is too chonky, there is also A34 which afaik is the smallest 64bit ARM core. Unfortunately I haven't seen anyone actually releasing chips based on it :( There are some socs with A35 cores though, that is probably lowest end that is actually available.

yjftsjthsd-h 3y ago

Actually I've been surprised at how much 64-bit dominates RISC-V even in the very lowest end of Linux-capable embedded. Perhaps I'm just in a bubble, though; not like I work in actual embedded stuff professionally.

adrian_b 3y ago

The price difference between something with Cortex-A55 64-bit cores and something with obsolete 32-bit cores is negligible. For modern home routers or security appliances you want them to be able to easily execute firewalls with complex sets of rules at multi-gigabit per second throughput, so that the router throughput should not be limited by the CPU instead of the Ethernet or WiFi interfaces. For this, you really need something like Cortex-A55. The routers with obsolete CPUs limit the performance without any worthwhile price reduction. On the other hand, for many embedded projects where a 32-bit CPU is the right choice, the developers choose Linux just because they are familiar with it and they are too lazy to read the manuals of some free real-time operating system, even if in fact the latter might require less development work and maintenance work for their software project.

pantalaimon 3y ago
The more bits you have to push around / the wider your registers and busses are, the more energy you are going to consume though.
- zokier 3y ago
  Is that actually measurable difference on modern process nodes and cores as big as Cortex-A?
zokier 3y ago
If even A55 is too chonky, there is also A34 which afaik is the smallest 64bit ARM core. Unfortunately I haven't seen anyone actually releasing chips based on it :( There are some socs with A35 cores though, that is probably lowest end that is actually available.