So you want to build an embedded Linux system? • Hacker News Board

Re: So you want to build an embedded Linux system?

#111

Post by cherryfire » Sun, Oct 18, 2020, 9:12 PM UTC

jaydcarlson wrote: post #101

contingencies wrote: post #78

The article really seems to be more about "so you want to design a custom PCB for a given embedded Linux capable application processor". While it is full of useful information and candid findings, there is usually negative business value in this approach as Jay admits lower down the article: I don’t think most people design PCBs around these raw parts anyway — the off-the-shelf SOMs are so ridiculously cheap (even on…

Please don't quote me out of context: "these raw parts" referred to the MediaTek parts specifically, not all the parts in this review. The only thing that SOMs provide is a processor + DRAM + PMIC. If you practice and become proficient at designing around application processors, it should take you no longer than 3-4 hours to get this component of the system (the processor, DRAM, and PMIC) laid out when working with t…

I think there's a lot of companies scared to roll out application processors instead of microcontrollers. I wonder what your thoughts are on if it can save development time due to Linux dev environment Vs baremetal.

Obviously lots of applications it would be impossible to use a 264 bga but I've been there with projects with 3 CAN buses and Ethernet plus flash memory and thought maybe we should be using a cortex A7.

I'm sure you know but file storage on microcontrollers can drive you insane ha ha and the same with graphics+TCP IP

Re: So you want to build an embedded Linux system?

#112

Post by spatular » Mon, Oct 19, 2020, 1:50 AM UTC

vitaminCPP wrote: post #108

spatular wrote: post #102

Earlier quoted context omitted.

MMU allows linux to provide a "flat" memory space to each userspace process. This memory space is assembled from 4KB pages that can be randomly dispersed throughout physical memory. Say, you want to malloc() 1MB of memory on a system that's been up for some time. Physical memory may not have a fitting continuos chunk of memory, but virtual memory of a newly created process will always have one, provided that there is…

Thanks. I realized that there are several types of MMU. I was thinking of the simple MMU (on 32bit MCU) that limit memory access. Not the one that provides the illusion of virtual addressing.

To be precise, that'd be called MPU -- memory protection unit.

Re: So you want to build an embedded Linux system?

#113

Post by bshanks » Tue, Oct 20, 2020, 5:11 AM UTC

joezydeco wrote: post #103

bshanks wrote: post #88

Earlier quoted context omitted.

Just out of curiosity, in your opinion, which are the major SOMs that you would consider for a 5+ year expected run lifetime?

It’s two-pronged. You need to find a chip line that has manufacturer guarantees for a long span, then a SOM integrator that will also guarantee a time span using that part. I’ve been happy with NXP (Freescale) for the former, obviously being a large automotive supplier has a benefit. For the SOM I’ve recently been using Toradex. They do a great job of making their SOMs comply to a common signal layout at the connecto…

Thanks