chumbyhackerboard:vga
Differences
This shows you the differences between two versions of the page.
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chumbyhackerboard:vga [2010/09/21 04:11] ladyada |
chumbyhackerboard:vga [2016/01/28 18:05] |
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| - | ====== DAC ====== | ||
| - | The LCD breakout has 6 bit x RGB output, which we can turn into a 6-bit DAC -> RGB analog 0.7Vpp into 75 ohms | ||
| - | use 278 & 556 ohm resistors for the R2R ladder, this will give you ~0.7v signal when plugged into a 75 ohm termination such as a monitor. | ||
| - | |||
| - | ====== VSync ====== | ||
| - | |||
| - | We want to get the Vsync to about 60hz | ||
| - | |||
| - | By default, the 'internal' LCD sync rate is 117 Hz | ||
| - | <code> | ||
| - | chumby-:/ # cat /proc/driver/chumbyfwfb/fb_stats | ||
| - | PXP frequency: 59 Hz | ||
| - | LCDIF frequency: 117 Hz | ||
| - | VSYNC Edge IRQs: 49077 | ||
| - | Cur Frame Done IRQs: 49224 | ||
| - | Missed PXP firings: 5 | ||
| - | </code> | ||
| - | |||
| - | This is set by the HW_CLKCTRL_PIX register | ||
| - | |||
| - | <code> | ||
| - | chumby-:/ # regutil -r HW_CLKCTRL_PIX | ||
| - | Value at 0x80040060: 0x0000001d | ||
| - | </code> | ||
| - | |||
| - | Lets divide the frequency by 2 which means multiplying the divider by two | ||
| - | |||
| - | <code> | ||
| - | chumby-:/ # regutil -w HW_CLKCTRL_PIX=0x38 | ||
| - | Setting 0x80040060: 0x0000000e -> 0x00000038 ok | ||
| - | </code> | ||
| - | |||
| - | <code> | ||
| - | chumby-:/ # cat /proc/driver/chumbyfwfb/fb_stats | ||
| - | PXP frequency: 32 Hz | ||
| - | LCDIF frequency: 62 Hz | ||
| - | VSYNC Edge IRQs: 69919 | ||
| - | Cur Frame Done IRQs: 70118 | ||
| - | Missed PXP firings: 5 | ||
| - | </code> | ||
| - | |||
| - | Actually, to get the closest to 60 Hz. I went with HW_CLKCTRL_PIX=0x37 (so says the tek 'scope) | ||
| - | |||
| - | How the Hsync is 17.08 KHz (we want 2x that 31.46 KHz) | ||
/home/ladyada/public_html/wiki/data/pages/chumbyhackerboard/vga.txt · Last modified: 2016/01/28 18:05 (external edit)
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