AdaWiki

====== 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. 



====== Horizontal Sync HW_LCDIF_VDCTRL2======

For the LCD, this is by default = 0x45000190

We want...

  * 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 + 96+ 48) = 0x60000320

====== Vsync HW_LCDIF_VDCTRL1 ======

For the LCD, this is by default = 0x0000011a (dec. 282)

We want...

  * 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 = 524 (0x20C)

====== HW_LCDIF_VDCTRL0 ======

<file>
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
</file>

-> 0x00340002

====== HW_LCDIF_TRANSFER_COUNT ======
By default, (32x0x240 LCD) =  0x00f00140

For 640x480 VGA it should be = 0x01E00280

====== HW_CLKCTRL_PIX ======

So the main clock is 454 right?

To get a pixel clock of 25.175 MHz, 454 MHz / 18 -> DIV = 0x12
CLKGATE = 0
DIV = 0x12 -> CLK of 21 Mhz

Hmm, guess our chip isnt running at 454? Or is it our scope? Try 0x0F for 25MHz  which matches with eveything else. Which means we're running at 375MHz?

===== Results? =====
PIXCLK = 0x0F

HSync = 31.3Khz (should be 31.46)

Vsync = 59.75 Hz (should be 60.04)

Vsync negative pulse = 63.9 uS (should be 63.57) (it is low from the negative edge of one HSync to another negative Hsync edge)

Hsync negative pulse = 3.83 uS (should be 3.81)
AdaWiki

User Tools

Site Tools

Page Tools
