|
:The total amount of blank pixels horizontally (including horizontal sync)
== Brendan's Original PostsSidenotes ==
>Any problems if I wikify this?
None at all - IMHO this information is required just to use VBE reliably; along with EDID (but you can find version 1.1 of the EDID data structures on Wikipedia) and details for the VBE DDC function (which VESA will let you have for free).
However, I should point out that this information is incomplete - the value of certain constants are missing from my original post. The default values for these constants are: CELL_GRAN_RND = 8, MARGIN_PRECENT = 1.8, MIN_PORCH_RND = 1, MIN_V_SYNC_AND_BACK_PORCH = 550, C_PRIME = 40 and M_PRIME = 600. I'd also mention that for my version of the formulas REFRESH_RATE_REQUIRED, V_FIELD_RATE_REQUIRED, H_FREQ_REQUIRED, PIXEL_FREQ_REQUIRED, V_FIELD_RATE, H_FREQ, PIXEL_FREQ are all in Hz (and not a mixture of Hz, KHz and MHz), which helps to simplify the formulas.
There's also some strange things that can happen with these formulas. For example, if any of the calculations give a negative result then it indicates invalid input (e.g. if the PIXEL_FREQ_REQUIRED input parameter is too low, then you can end up with horizontal blanking that takes "negative N us"). In practice, some of these calculations probably have an allowed range (e.g. things like "horizontal blanking must be >= 20% of the horizontal total") but I've been unable to find anything indicating what the allowed ranges for anything is. :(
---------
This is for my own reference, and in case anyone is wondering what they look like... The GTF formulas.
There's actually 3 separate calculations here - finding all timing parameters from X & Y resolution and desired refresh rate, finding all timing parameters from X & Y resolution and desired horizontal frequency, and finding all timing parameters from X & Y resolution and desired pixel clock frequency.
===GTF Formulas For Using Desired Refresh Rate===
<pre>
H_PIXELS_RND = ( ROUND ( H_PIXELS / CELL_GRAN_RND ) ) * CELL_GRAN_RND
IF ( INTERLACE_REQUIRED == "y") {
V_LINES_RND = ROUND ( V_LINES / 2 )
V_FIELD_RATE_REQUIRED = REFRESH_RATE_REQUIRED * 2
INTERLACE = 0.5
} else {
V_LINES_RND = ROUND ( V_LINES) )
V_FIELD_RATE_REQUIRED = REFRESH_RATE_REQUIRED
INTERLACE = 0
}
IF ( MARGINS_REQUIRED == "y" ) {
TOP_MARGIN_LINES = ROUND ( MARGIN_PRECENT / 100 * V_LINES_RND )
BOTTOM_MARGIN_LINES = ROUND ( MARGIN_PRECENT / 100 * V_LINES_RND )
LEFT_MARGIN_PIXELS = ( ROUND ( ( H_PIXELS_RND * MARGIN_PRECENT / 100 / CELL_GRAN_RND ) , 0 ) ) * CELL_GRAN_RND
RIGHT_MARGIN_PIXELS = ( ROUND ( ( H_PIXELS_RND * MARGIN_PRECENT / 100 / CELL_GRAN_RND ) , 0 ) ) * CELL_GRAN_RND
} else {
TOP_MARGIN_LINES = 0
BOTTOM_MARGIN_LINES = 0
LEFT_MARGIN_PIXELS = 0
RIGHT_MARGIN_PIXELS = 0
}
H_PERIOD_ESTIMATE = ( 1 / V_FIELD_RATE_REQUIRED - MIN_V_SYNC_AND_BACK_PORCH / 1000000 ) / ( V_LINES_RND + 2 * TOP_MARGIN_LINES + MIN_PORCH_RND + INTERLACE ) * 1000000
V_SYNC_AND_BACK_PORCH = ROUND ( MIN_V_SYNC_AND_BACK_PORCH / H_PERIOD_ESTIMATE )
V_BACK_PORCH = V_SYNC_AND_BACK_PORCH - V_SYNC_RND
TOTAL_V_LINES = V_LINES_RND + TOP_MARGIN_LINES + BOTTOM_MARGIN_LINES + V_SYNC_AND_BACK_PORCH + INTERLACE + MIN_PORCH_RND
V_FIELD_RATE_ESTIMATE = 1000000 / H_PERIOD_ESTIMATE / TOTAL_V_LINES
H_PERIOD = H_PERIOD_ESTIMATE * V_FIELD_RATE_ESTIMATE / V_FIELD_RATE_REQUIRED
V_FIELD_RATE = 1000000 / H_PERIOD / TOTAL_V_LINES
IF ( INTERLACE_REQUIRED == "y") {
V_FRAME_RATE = V_FIELD_RATE / 2
} else {
V_FRAME_RATE = V_FIELD_RATE
}
TOTAL_ACTIVE_PIXELS = H_PIXELS_RND + LEFT_MARGIN_PIXELS + RIGHT_MARGIN_PIXELS
IDEAL_DUTY_CYCLE = C_PRIME - M_PRIME * H_PERIOD / 1000
H_BLANK_PIXELS = ( ROUND ( ( TOTAL_ACTIVE_PIXELS * IDEAL_DUTY_CYCLE / ( 100 - IDEAL_DUTY_CYCLE ) / ( 2 * CELL_GRAN_RND ) ) ) ) * 2 * CELL_GRAN_RND
TOTAL_PIXELS = TOTAL_ACTIVE_PIXELS + H_BLANK_PIXELS
PIXEL_FREQ = TOTAL_PIXELS / H_PERIOD * 1000000
H_FREQ = 1 / H_PERIOD</pre>
===GTF Formulas For Using Horizontal Frequency===
<pre>
H_PIXELS_RND = ( ROUND ( H_PIXELS / CELL_GRAN_RND ) ) * CELL_GRAN_RND
IF ( INTERLACE_REQUIRED == "y") {
V_LINES_RND = ROUND ( V_LINES / 2 )
INTERLACE = 0.5
} else {
V_LINES_RND = ROUND ( V_LINES) )
INTERLACE = 0
}
IF ( MARGINS_REQUIRED == "y" ) {
TOP_MARGIN_LINES = ROUND ( MARGIN_PRECENT / 100 * V_LINES_RND )
BOTTOM_MARGIN_LINES = ROUND ( MARGIN_PRECENT / 100 * V_LINES_RND )
LEFT_MARGIN_PIXELS = ( ROUND ( ( H_PIXELS_RND * MARGIN_PRECENT / 100 / CELL_GRAN_RND ) , 0 ) ) * CELL_GRAN_RND
RIGHT_MARGIN_PIXELS = ( ROUND ( ( H_PIXELS_RND * MARGIN_PRECENT / 100 / CELL_GRAN_RND ) , 0 ) ) * CELL_GRAN_RND
} else {
TOP_MARGIN_LINES = 0
BOTTOM_MARGIN_LINES = 0
LEFT_MARGIN_PIXELS = 0
RIGHT_MARGIN_PIXELS = 0
}
H_FREQ = H_FREQ_REQUIRED
V_SYNC_AND_BACK_PORCH = ROUND ( MIN_V_SYNC_AND_BACK_PORCH * H_FREQ / 1000000 )
V_BACK_PORCH = V_SYNC_AND_BACK_PORCH - V_SYNC_RND
TOTAL_V_LINES = V_LINES_RND + TOP_MARGIN_LINES + BOTTOM_MARGIN_LINES + INTERLACE + V_SYNC_AND_BACK_PORCH + MIN_PORCH_RND
V_FIELD_RATE = H_FREQ / TOTAL_V_LINES
IF ( INTERLACE_REQUIRED == "y") {
V_FRAME_RATE = V_FIELD_RATE / 2
} else {
V_FRAME_RATE = V_FIELD_RATE
}
TOTAL_ACTIVE_PIXELS = H_PIXELS_RND + RIGHT_MARGIN_PIXELS + LEFT_MARGIN_PIXELS
IDEAL_DUTY_CYCLE = C_PRIME - ( M_PRIME / H_FREQ )
H_BLANK_PIXELS = ( ROUND ( TOTAL_ACTIVE_PIXELS * IDEAL_DUTY_CYCLE / ( 100 - IDEAL_DUTY_CYCLE ) / ( 2 * CELL_GRAN_RND ) ) ) * 2 * CELL_GRAN_RND
TOTAL_PIXELS = TOTAL_ACTIVE_PIXELS + H_BLANK_PIXELS
H_PERIOD = 1 / H_FREQ
PIXEL_FREQ = TOTAL_PIXELS * H_FREQ
</pre>
===GTF Formulas For Using Pixel Clock Frequency===
<pre>
H_PIXELS_RND = ( ROUND ( H_PIXELS / CELL_GRAN_RND ) ) * CELL_GRAN_RND
IF ( INTERLACE_REQUIRED == "y") {
V_LINES_RND = ROUND ( V_LINES / 2 )
INTERLACE = 0.5
} else {
V_LINES_RND = ROUND ( V_LINES) )
INTERLACE = 0
}
PIXEL_FREQ = PIXEL_FREQ_REQUIRED
IF ( MARGINS_REQUIRED == "y" ) {
TOP_MARGIN_LINES = ROUND ( MARGIN_PRECENT / 100 * V_LINES_RND )
BOTTOM_MARGIN_LINES = ROUND ( MARGIN_PRECENT / 100 * V_LINES_RND )
LEFT_MARGIN_PIXELS = ( ROUND ( ( H_PIXELS_RND * MARGIN_PRECENT / 100 / CELL_GRAN_RND ) , 0 ) ) * CELL_GRAN_RND
RIGHT_MARGIN_PIXELS = ( ROUND ( ( H_PIXELS_RND * MARGIN_PRECENT / 100 / CELL_GRAN_RND ) , 0 ) ) * CELL_GRAN_RND
} else {
TOP_MARGIN_LINES = 0
BOTTOM_MARGIN_LINES = 0
LEFT_MARGIN_PIXELS = 0
RIGHT_MARGIN_PIXELS = 0
}
TOTAL_ACTIVE_PIXELS = H_PIXELS_RND + RIGHT_MARGIN_PIXELS + LEFT_MARGIN_PIXELS
IDEAL_H_PERIOD = ( ( C_PRIME - 100 ) + ( SQRT ( ( ( 100 - C_PRIME ) ^ 2 ) + ( 0.4 * M_PRIME * ( TOTAL_ACTIVE_PIXELS + RIGHT_MARGIN_PIXELS + LEFT_MARGIN_PIXELS ) / PIXEL_FREQ / 1000000 ) ) ) ) / 2 / M_PRIME * 1000
IDEAL_DUTY_CYCLE = C_PRIME - ( M_PRIME * IDEAL_H_PERIOD / 1000 )
H_BLANK_PIXELS = ( ROUND ( TOTAL_ACTIVE_PIXELS * IDEAL_DUTY_CYCLE / ( 100 - IDEAL_DUTY_CYCLE ) / ( 2 * CELL_GRAN_RND ) ) ) * 2 * CELL_GRAN_RND
TOTAL_PIXELS = TOTAL_ACTIVE_PIXELS + H_BLANK_PIXELS
H_FREQ = PIXEL_FREQ / TOTAL_PIXELS
H_PERIOD = 1 / H_FREQ
V_SYNC_AND_BACK_PORCH = ROUND ( MIN_V_SYNC_AND_BACK_PORCH * H_FREQ / 1000000 )
V_BACK_PORCH = V_SYNC_AND_BACK_PORCH - V_SYNC_RND
TOTAL_V_LINES = V_LINES_RND + TOP_MARGIN_LINES + BOTTOM_MARGIN_LINES + INTERLACE + V_SYNC_AND_BACK_PORCH + MIN_PORCH_RND
V_FIELD_RATE = H_FREQ / TOTAL_V_LINES
IF ( INTERLACE_REQUIRED == "y") {
V_FRAME_RATE = V_FIELD_RATE / 2
} else {
V_FRAME_RATE = V_FIELD_RATE
}
</pre>
Note: The "round()" function here rounds to the nearest integer (it doesn't round down or round up).
Cheers,
Brendan
=== More VESA Rants ===
I think part of the problem is that the original GTF formulas from VESA are copied from their spreadsheet, so that (for a silly example) instead of doing something like:
|