3 ms·

what is the memory management unit supposed to do on embedded computers? I'd rather like one for 5$ without mmu.

alexisread 4y ago
This chip has 4 cores, and I believe they all share the same memory bus ie. Each core can access the 64GB ram directly. There is also 768K sram for low power use. Only the RV64 large core has an mmu, the two RV32 cores don't. I think the chip's main use could be robotics- the lowest power core for networking, npu for image processing, the mid core for simple tasks and the large core for Linux and complex tasks eg. Navigation. With the shared memory bus, you can hand over tasks between the cores. You may not have the same software running on each core, but the data can be the same. For your use then, you could just use the lowest power microcontroller with 64GB ram. You can't get that ability anywhere else.
- Tepix 4y ago
  > the 64GB ram It's 64 MB RAM
  - alexisread 4y ago
    Ah yes thanks, still pretty good though for on-package for £3-odd (UK price). https://m.aliexpress.com/item/1005004970779483.html https://m.aliexpress.com/item/1005004970779483.html
    - aswanson 4y ago
      Any experience with this board? Toolchain, etc?
      - alexisread 4y ago
        Not yet- I have a maix M1s dock full package on order, so hope to try it shortly. Sipeed supply a connector to be able to flash their board easily, and they seem to have an IDE for various use cases. I'm hoping the MCU in the chip is the same as the BL602 chip- the 602 has a fully opensource firmware for the radio and cpu, can run zig and lora: https://lupyuen.github.io/ https://lupyuen.github.io/ For me, I'm looking forward to using a riscV MCU with a decent amount of ram, as a fixed platform to build an OS on.
        aswanson 4y ago
        Great, keep me posted on your progress. Just ordered 2. The price point was just too good to pass up for that much horsepower and ram.
        monocasa 4y ago
        > I'm hoping the MCU in the chip is the same as the BL602 chip It's not, but it's similar. The BL602 has a SiFive E24, the cores in the BL602 are all T-Head cores (the mid core is a T-Head e907).
- monocasa 4y ago
  > This chip has 4 cores 3 cores > For your use then, you could just use the lowest power microcontroller with 64GB ram. You can't get that ability anywhere else. I don't think the LP core has access to PSRAM. So most of the networking would run on the mid core, and the LP core just makes decisions to wake up a bigger core based on the events it sees.
  - alexisread 4y ago
    I'm counting the NPU :) I couldn't find anything in the datasheet about the LP core PSRAM access - do you have a confirmation on that? It'd be a shame if it didn't, but kinda makes sense with the 768K sram. I was hoping it had access to both.
unwind 4y ago
It allows you to use Linux, which is a sellable bullet point. Might also be useful sometimes, and allow knowledge sharing, increase portability and so on.
guerrilla 4y ago
You can't run Linux without an MMU. There are thousands of MCUs that can't run Linux for much cheaper than 5$...
- jesprenj 4y ago
  https://www.kernel.org/doc/Documentation/nommu-mmap.txt https://www.kernel.org/doc/Documentation/nommu-mmap.txt
  - guerrilla 4y ago
    Ok fair enough, Linux can't run normally without an MMU. It kind of defeats the purpose of using a UNIX, but yes, you get all the Linux drivers and the UNIX API for free.
    - monocasa 4y ago
      You still have processes and mutual protection between them and the kernel with no-MMU, they just get less options about where they can mmap(2) and you have to vfork(2) instead of fork(2). Otherwise it feels like a pretty standard Linux.
      - joezydeco 4y ago
        Applications built with dynamic libraries are a pain in the ass with ucLinux.
        monocasa 4y ago
        It is an archs without position independent code. As long as you have FDPIC, it's fairly painless.
      - jesprenj 4y ago
        What about interprocess protection? Do permissions make sense on nommu, can a process edit another's RAM?

This chip has 4 cores, and I believe they all share the same memory bus ie. Each core can access the 64GB ram directly. There is also 768K sram for low power use. Only the RV64 large core has an mmu, the two RV32 cores don't. I think the chip's main use could be robotics- the lowest power core for networking, npu for image processing, the mid core for simple tasks and the large core for Linux and complex tasks eg. Navigation. With the shared memory bus, you can hand over tasks between the cores. You may not have the same software running on each core, but the data can be the same. For your use then, you could just use the lowest power microcontroller with 64GB ram. You can't get that ability anywhere else.

Tepix 4y ago
> the 64GB ram It's 64 MB RAM
- alexisread 4y ago
  Ah yes thanks, still pretty good though for on-package for £3-odd (UK price). https://m.aliexpress.com/item/1005004970779483.html https://m.aliexpress.com/item/1005004970779483.html
  - aswanson 4y ago
    Any experience with this board? Toolchain, etc?
    - alexisread 4y ago
      Not yet- I have a maix M1s dock full package on order, so hope to try it shortly. Sipeed supply a connector to be able to flash their board easily, and they seem to have an IDE for various use cases. I'm hoping the MCU in the chip is the same as the BL602 chip- the 602 has a fully opensource firmware for the radio and cpu, can run zig and lora: https://lupyuen.github.io/ https://lupyuen.github.io/ For me, I'm looking forward to using a riscV MCU with a decent amount of ram, as a fixed platform to build an OS on.
      - aswanson 4y ago
        Great, keep me posted on your progress. Just ordered 2. The price point was just too good to pass up for that much horsepower and ram.
      - monocasa 4y ago
        > I'm hoping the MCU in the chip is the same as the BL602 chip It's not, but it's similar. The BL602 has a SiFive E24, the cores in the BL602 are all T-Head cores (the mid core is a T-Head e907).
monocasa 4y ago
> This chip has 4 cores 3 cores > For your use then, you could just use the lowest power microcontroller with 64GB ram. You can't get that ability anywhere else. I don't think the LP core has access to PSRAM. So most of the networking would run on the mid core, and the LP core just makes decisions to wake up a bigger core based on the events it sees.
- alexisread 4y ago
  I'm counting the NPU :) I couldn't find anything in the datasheet about the LP core PSRAM access - do you have a confirmation on that? It'd be a shame if it didn't, but kinda makes sense with the 768K sram. I was hoping it had access to both.

unwind 4y ago

It allows you to use Linux, which is a sellable bullet point. Might also be useful sometimes, and allow knowledge sharing, increase portability and so on.

guerrilla 4y ago

You can't run Linux without an MMU. There are thousands of MCUs that can't run Linux for much cheaper than 5$...

jesprenj 4y ago
https://www.kernel.org/doc/Documentation/nommu-mmap.txt https://www.kernel.org/doc/Documentation/nommu-mmap.txt
- guerrilla 4y ago
  Ok fair enough, Linux can't run normally without an MMU. It kind of defeats the purpose of using a UNIX, but yes, you get all the Linux drivers and the UNIX API for free.
  - monocasa 4y ago
    You still have processes and mutual protection between them and the kernel with no-MMU, they just get less options about where they can mmap(2) and you have to vfork(2) instead of fork(2). Otherwise it feels like a pretty standard Linux.
    - joezydeco 4y ago
      Applications built with dynamic libraries are a pain in the ass with ucLinux.
      - monocasa 4y ago
        It is an archs without position independent code. As long as you have FDPIC, it's fairly painless.
    - jesprenj 4y ago
      What about interprocess protection? Do permissions make sense on nommu, can a process edit another's RAM?