chumbyhackerboard:vga
Differences
This shows you the differences between two versions of the page.
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chumbyhackerboard:vga [2010/09/21 04:45] 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) | ||
| - | |||
| - | |||
| - | THIS IS ALL WRONG. START OVER! | ||
| - | |||
| - | ====== Horizontal Sync HW_LCDIF_VDCTRL2====== | ||
| - | |||
| - | For the LCD, this is by default = 0x45000190 | ||
| - | |||
| - | Per horizontal line: 640 pixels | ||
| - | Front porch: 16 pixels | ||
| - | Sync pulse width: 96 pixels | ||
| - | Back porch: 48 pixels | ||
| - | |||
| - | SO! | ||
| - | |||
| - | HW_LCDIF_VDCTRL2 = (96) << 24 | (640 + 16 + 48) = 0x600002C0 | ||
| - | |||
| - | ====== Vsync HW_LCDIF_VDCTRL1 ====== | ||
| - | |||
| - | For the LCD, this is by default = 0x0000011a (dec. 282) | ||
| - | |||
| - | Per vertical line: 480 horizontal lines | ||
| - | Front porch: 11 horizontal lines | ||
| - | Sync pulse: 2 horizontal lines | ||
| - | back porch: 31 horizontal lines | ||
| - | |||
| - | so HW_LCDIF_VDCTRL1 = 542 (0x21e) | ||
| - | |||
| - | ====== HW_LCDIF_VDCTRL0 ====== | ||
| - | |||
| - | VSYNC_OEB = 0 (generate vsync) | ||
| - | ENABLE_PRESENT = 0 (no enable necessary) | ||
| - | 0x0 | ||
| - | |||
| - | VSYNC_POL = 0 (negative sync!) | ||
| - | HSYNC_POL = 0 (negative sync!) | ||
| - | DOTCLK_POL = D/C | ||
| - | ENABLE_POL = D/C | ||
| - | 0x0 | ||
| - | |||
| - | VSYNC_PERIOD_UNIT = 1 (count in lines) | ||
| - | VSYNC_PULSE_WIDTH_UNIT = 1 (count in lines) | ||
| - | 0x3 | ||
| - | |||
| - | HALF_LINE = 0 | ||
| - | HALF_LINE_MODE = 1 (no half line for vga, right?) | ||
| - | 0x4 | ||
| - | |||
| - | VSYNC_PULSE_WIDTH = 2 | ||
| - | 0x2 | ||
| - | |||
| - | -> 0x00340002 | ||
| - | |||
| - | ====== HW_LCDIF_TRANSFER_COUNT ====== | ||
| - | By default, (32x0x240 LCD) = 0x00f00140 | ||
| - | |||
| - | For 640x480 VGA it should be = 0x01E00280 | ||
| - | |||
| - | ====== HW_CLKCTRL_PIX ====== | ||
| - | |||
| - | CLKGATE = 0 | ||
| - | DIV = 0x11 | ||
| - | |||
| - | To get HSync of 31.4Khz & Vsync of 58 Hz | ||
| - | |||
| - | |||
/home/ladyada/public_html/wiki/data/pages/chumbyhackerboard/vga.txt · Last modified: 2016/01/28 18:05 (external edit)
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