On Mon, Jun 15, 2015 at 10:57 AM, Pavel Pisa <p...@cmp.felk.cvut.cz> wrote: > Hello Joel and Qiao Yang, > > On Monday 15 of June 2015 15:39:15 Joel Sherrill wrote: >> On 6/14/2015 5:31 AM, QIAO YANG wrote: >> > 1. Will rpi bsp has any kernel command line setup like i386? This would >> > let us to choose fb console port or serial console port . Or maybe we >> > just use compiler macro to enable/disable graphic console output? >> >> How does the Linux kernel get its boot arguments? The pc386 BSP gets its >> arguments the same way. Then there are some bsp command line methods to >> access the parameters. The start code passes a string pointer to boot_card >> for this to happen. > > Linux kernel on ARM can use two mechanism to obtain command line > options from boot-loader > > The first is ATAGs mechanisms. This mechanism generally provides > machine specific code to the kernel and sequence of 32-bit > size and tag/data type blocks. ATAGS structure usually starts > at memory address 0x100. > > The second, preferred now method, is to copy to RAM or prepare > flattened device tree data (FDT) structure to the RAM from bootloader. > This mechanism allows to describe all (allmost) machine parameters > and peripherals connection to different non-enumerated busses. > (Runtime detection is used for devices connected to enumerated busses). > > Older Videocore boot firmware did not provide FDT method nor > merging but actual version is able to prepare device tree data > in memory, merge commandline and optional specified device > tree fragments and start kernel > > The short overview is placed on slide 13 and 14 of my presentation > > http://installfest.cz/if15/slides/pisa_rpi.pdf > > Complete Videocore firmware options are described there > > https://www.raspberrypi.org/documentation/configuration/config-txt.md > > Description of Linux kernel booting on ARM is described > in Linux kernel sources documentation > > https://www.kernel.org/doc/Documentation/arm/Booting > > The mainline U-boot switched to FDT based method long time ago > and RPi branch provides FDT support now as well. I have build > such U-boot and use FDT configured kernel on RPi with U-boot > and direct boot from firmware for some time already. > > It would be great to provide some basic device tree support > to RTEMS because it would solve parameters parsing and > device recognition/base addresses etc. on all U-boot supported > ARM platforms in future. Searching for nodes in device > tree binary structure is quite easy. Knowledge how to interpret > the names and hierarchy can be sometimes more complex but > it is described in Linux kernel sources. > Chris Johns had an FDT implementation floating around, I think.
> Pointers to many FDT documents can be found there > > http://elinux.org/Device_Tree > > and I would help with testing, ideas and may it be with some > code if time allows. > > But it is probably task for separate GSoC or major project. > >> > Something waiting to be done: >> > 1. graphic console need the keyboard implementation . I would like to >> > know the status of keyboard implementation. > > Most common is USB keyboard on RPi so it depends on USB support project. > But for graphic output is is not so critical and for real embedded > systems small keyboard on SPI can be usable as well. > > SPI on RPi is not/should not be a problem. I can provide examples > of SPI based keyboard support for RTEMS and even HW implementation > used on our other systems. > > Best wishes, > > Pavel Pisa > _______________________________________________ > devel mailing list > devel@rtems.org > http://lists.rtems.org/mailman/listinfo/devel _______________________________________________ devel mailing list devel@rtems.org http://lists.rtems.org/mailman/listinfo/devel
