System information

4.2 Graphic Card Implementation Layout
for BAR 1 (RPC is explained in section 4.3.3). Following an example of the Request Buffer
content:
...
0000033d 000003d5 00003600 ffffffff
0000027c 000b806c 00007053 ffffffff
0000033e 000003d4 0000000e ffffffff
...
This example of a content of the Request Buffer is organized according to the data structure
illustrated in figure 4.8. The first double word contains the BAR number, byteenable and
the type of PCI request. With the aid of these information, the BAR Switch driver selects
the appropriate callback function. The second and third double word contain the address
and data of the PCI access which will transmit to the callback function. The BAR Switch
driver will also executes the callback function, if the host tries a read request to the PCI
target interface. The related driver has to write the requested value into the PCI read buffer.
After the execution of the callback function, the BAR Switch driver informs the PCI Target
Control unit about the valid entry inside the read buffer. Section 4.2.2 illustrates this
process.
The VGA Driver
The VGA driver undertakes the processing of the VGA protocol. According to the VGA
protocol, the driver administrates the four video planes [56]. These planes represent the
video screen content. They are located in the upper part of the 32 MB SDRAM memory.
Figure E.1 depicts the memory map of the SDRAM module. The content of the VGA
registers define the video mode. A mode defines how the video plane content has to be
processed to a picture. The registers are managed inside the driver. They are not directly
accessible with a user space program. Instead, the driver creates an entry inside the device
file system. The files in this file system represent an interface to a hardware device. Table
4.3 lists the directory tree of the VGA driver inside the device file system.
Device File Description
/dev/charm/vga/plane[0-3] Contains the content of the video planes
/dev/charm/vga/register Contains the content of the VGA register
/dev/charm/vga/text Video memory in text mode
/dev/charm/vga/palette Actual color palette
/dev/charm/vga/control Provides information about the video
mode and VGA settings
Table 4.3: Device file system entry of the VGA driver.
The content of the VGA planes is either provided by device files or for a fast access
directly accessible via memory-mapped file I/O. Thereby, the planes can be mapped from
the SDRAM to the user space. The start of the character content in a text mode is not fixed.
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