7. Converting XFree86 timing values into frame buffer device timings

An XFree86 mode line consists of the following fields:

    "800x600"     50      800  856  976 1040    600  637  643  666
    < name >     DCF       HR  SH1  SH2  HFL     VR  SV1  SV2  VFL
    

The frame buffer device uses the following fields:

pixclock

pixel clock in ps (pico seconds)

left_margin

time from sync to picture

right_margin

time from picture to sync

upper_margin

time from sync to picture

lower_margin

time from picture to sync

hsync_len

length of horizontal sync

vsync_len

length of vertical sync

Pixelclock

• xfree: in MHz
• fb: In Picoseconds (ps)
• pixclock = 1000000 / DCF

Horizontal timings

• left_margin = HFL - SH2
• right_margin = SH1 - HR
• hsync_len = SH2 - SH1

Vertical timings

• upper_margin = VFL - SV2
• lower_margin = SV1 - VR
• vsync_len = SV2 - SV1

Good examples for VESA timings can be found in the XFree86 source tree, under xc/programs/Xserver/hw/xfree86/doc/modeDB.txt.