Re: [seL4] VGA buffer as stdout

Hello, I tested the code on a real hardware, and it ends at the same point - no output after "Starting node #0..." Can you replicate the results? M On Tue, Aug 8, 2017 at 2:09 PM, Michal Podhradsky wrote:

Hi Adrian, Kofi,

I followed your advice, and just as a proof of concept I redefined putConsoleChar from here: https://github.com/seL4/seL4/ blob/master/src/plat/pc99/machine/io.c#L38 On top of printing on serial port, I added a line with text_ega_putchar((int) a); - so now the character is printed both on serial out and VGA screen.

I added the scrolling etc functions from https://github.com/seL4/util_ libs/blob/master/libplatsupport/src/plat/pc99/ega.c to take care of line wraps and control characters (\n, \t, etc). Then I compiled the basic keyboard camkes example: https://github.com/seL4/camkes/tree/master/apps/keyboard and I run the program in qemu with -vga -std option.

I can see the kernel booting up on the screen as well as the serial out, but as soon as sel4 drops into userspace ("Starting node #0 with APIC ID 0") , it stops outputting anything (user program not running?);

The screenshot is here: https://drive.google.com/file/d/ 0B8h93vAE2c4ibmRKQkdZU3EtcUk/view?usp=sharing

Any ideas what am I missing?

Regards M

On Wed, Aug 2, 2017 at 4:18 AM, Andrew Warkentin wrote:

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Assuming you are talking about text mode VGA then having the kernel render to such a buffer is not particularly difficult. Instead of the 0xB8000 address though I would consider using the supposed multiboot video mode, and perhaps falling back to the buffer at 0xB8000 if no multiboot video mode provided, that would provide the most reliability. You will need to * Emulate the vt100 codes in the seL4 messages, or disable colored output (which I believe is all we use control codes for) * Handle end of line detection and scrolling Whilst not using multiboot an old slightly bitrotted user level example of what you are proposing is https://github.com/seL4/util_libs/blob/master/libplatsupport /src/plat/pc99/ega.c

If you want to use a linear graphics mode though (and you don't want to change display modes later on) then obviously it's a little more complicated as you'll have to do font rendering. Not that rendering the equivalent of a monospaced text mode onto a linear graphics mode is particularly difficult though. Note that we currently have not written graphics support beyond

On 8/2/17, Adrian.Danis@data61.csiro.au wrote: the

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multiboot graphics mode that the kernel can request from its loader, in particular we do not have any code that would allow you to change the screen mode later on at user level.

Like I said before I am planning to exclusively use a linear framebuffer rather than hardware text mode (which is a relic from an era when hardware wasn't powerful enough to do software text modes with reasonable performance, and I believe it's not supported at all under UEFI), and I'm planning to have it just emulate a dumb terminal (i.e. no escape codes; I don't want to bloat the kernel with a VT100 emulator just for displaying early boot messages). I was thinking of using the framebuffer console code from coreboot's libpayload (which only emulates a dumb terminal and is very lightweight).

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Asking the kernel to stop using its debug output device, to allow the user to start using wholly for its own purposes, is something that could be useful to add. Probably would have to be another 'debug' syscall, and could function as a dynamic enabling/disabling of kernel printing.

I was going to have the kernel automatically disable the early console immediately before it loads the root server, so there would be no need for an API (at least not under UX/RT). UX/RT's root server will contain its own early console emulator (possibly also based on that of libpayload) that will provide a minimal subset of a Unix terminal device to programs run during early boot (initializing the console emulator will be the first thing that the root server does). A full-featured DRM/DRI graphics driver and console emulator will take over before the root volume is mounted.

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