觀察筆記

A framebuffer is a video output device that drives a video display from a memory buffer containing a complete frame of data.

Framebuffer 的架構，是利用 mmap 向 kernel 映射出 "顯示記憶體"區塊(註一、其他memory access的方式 )，讓linux的user可以透過framebuffer device(而不需要透過底層的driver)直接對display memory進行讀寫操作。

The information in the buffer typically consists of color values for every pixel (point that can be displayed) on the screen.

Framebuffer裡主要是顯示資訊。

Color values are commonly stored in 1-bit monochrome, 4-bit palettized, 8-bit palettized, 16-bit highcolor and 24-bit truecolor formats. An additional alpha channel is sometimes used to retain information about pixel transparency.

以上是Color values的格式 Orz 不是很懂。

The total amount of the memory required to drive the framebuffer depends on the resolution of the output signal, and on the color depth and palette size.

而所會用到的記憶體大小就看你要顯示的多清楚了！

註一、其他memory access的方式；

• Mapping the entire framebuffer to a given memory range.
• Port commands to set each pixel, range of pixels or palette entry.
• Mapping a memory range smaller than the framebuffer memory, then bank switching as necessary.

Linux frame buffer 驅動程式開發簡報下載