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In x86, the kernel can write to 0xB8000 and have ASCII characters displayed on screen, after some setup of the VGA device. Is there a similar standard mechanism for the kernel to display messages during boot? If not, do chip manufacturers tend to create their own mechanisms for this, or is an external serial-to-video device (FPGA, or serial link to a PC) a better option for this?

Leonora Tindall
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    Your question is based on a misconception - it is not the x86 architecture which enables the capability of which you speak, but rather the legacy IBM PC design heritage. Other 8086 designs not intended to be IBM compatible either didn't have that capability, or implemented it differently. – Chris Stratton Apr 21 '15 at 03:28
  • Oh, interesting. So it is a chipset feature rather than an architectural one? – Leonora Tindall Apr 21 '15 at 13:41
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    A text buffer like that on MDA/CGA/HGC/EGA/VGA etc was a feature of the discrete CRT controller and character ROM, enabled by firmware (bios) setting values in registers. Later on that might have been folded into some chipsets with "onboard VGA" If some other device supports a character mode display, or if it requires software to render text to a bitmapped framebuffer, would depend on the details of that device. Generally if you have a display, it's useful to come up with a solution to put boot messages there - but you almost always want to break out a serial port for use even earlier. – Chris Stratton Apr 21 '15 at 14:13
  • So it's entirely implementation-specific, and I basically need to do it myself. Thanks! Put your comment as an answer, I'll accept it. – Leonora Tindall Apr 21 '15 at 15:26

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