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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.
We want to get the Vsync to about 60hz
By default, the 'internal' LCD sync rate is 117 Hz
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
This is set by the HW_CLKCTRL_PIX register
chumby-:/ # regutil -r HW_CLKCTRL_PIX Value at 0x80040060: 0x0000001d
Lets divide the frequency by 2 which means multiplying the divider by two
chumby-:/ # regutil -w HW_CLKCTRL_PIX=0x38 Setting 0x80040060: 0x0000000e -> 0x00000038 ok
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
Actually, to get the closest to 60 Hz. I went with HW_CLKCTRL_PIX=0x37 (so says the tek 'scope)