>> Define "traditional embedded system" <G> your definition is correct!
On Monday, July 29, 2019 at 1:18:33 PM UTC-4, Dennis Lee Bieber wrote: > > On Mon, 29 Jul 2019 05:56:00 -0700 (PDT), Jani > <amer...@gmail.com <javascript:>> declaimed the > following: > > >A traditional embedded system boots from flash memory and code runs from > >flash memory. Usually application isn't copied to RAM, only read/write > >variables are copied to RAM. > > Define "traditional embedded system" <G> > > In the readily available market, what you describe above falls > into the > Arduino, Tiva-C, Adafruit Metro, Parallax Propeller cards -- which are > classed as "microCONTROLLER" boards. The closest they get to having an OS > might be applications using something like FreeRTOS (or TI-RTOS for the > Tiva-C) -- ie: the application /is/ the OS. The Flash memory on such > systems is directly mapped into the processor address space along with the > RAM and any memory-mapped I/O devices/ports. > > >Does system running embedded Linux execute from RAM? > > > > Once you specify Linux, you mostly are talking "microCOMPUTER" > with a > full up OS and related file system, "ad-hoc" process creation (in an RTOS, > all processes tend to be predefined and created on start-up), etc. Any > Flash memory tends to be configured as an I/O device and is part of the > file-system, not part of the processor memory address space. > > This does not preclude designing a board in which some of the > processor > address space is Flash memory. It may even be possible to build a Linux > kernel (or whatever that binary file that is used during booting -- I'm > not > an OS developer) image that can be stored in flash and directly jumped to > during booting (it would probably offer much faster start-up if the boot > load just has to set up processor registers/zero RAM and can jump directly > into the OS -- rather than copying a core image file into RAM and jumping > to it). I have seen a card which did have memory-mapped Flash (I had to > port benchmarks to it some years ago, and the benchmarks ran as pure > start-up code from Flash). > > BeagleBone and Raspberry-PI, however, do not have memory-mapped > Flash; > they run from RAM and load the core image from a defined file-system on > I/O > device Flash. > > >I need to know what size DRAM I need for my embedded Linux system? If > >Linux distribution takes up 3GB in SD card. Then, does this mean I need > >3GB DRAM? > > BBB has a 4GB eMMC (or use SDHC up to 32GB) but only 512MB of RAM. > The > R-Pi3B doesn't have on-board eMMC, so uses SDHC up to 32GB, and has 1GB of > RAM (it also has a quad-core processor). The latest R-Pi4B can be had with > 1, 2, or 4GB of RAM. > > Also take into account that, if you have external storage (disk), > these > systems can be configured with a swap partition/file and could move idle > data/code out to swap. OTOH; once you start swapping you lose much of any > realtime capabilities -- you could be caught with swapping latency if, > say, > a very rare interrupt occurs and the handler is not in core. > > > > -- > Wulfraed Dennis Lee Bieber AF6VN > wlf...@ix.netcom.com <javascript:> > http://wlfraed.microdiversity.freeddns.org/ > > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/beagleboard/00fc6f66-77bc-4c6a-9c59-e6d7dba7f934%40googlegroups.com.
