Programming the vertical generation registers to the values shown in Table: Example Vertical Generation Register Inputs (Alternate 4:2:0 Chroma) will result in the video timing signal outputs shown in This Figure .
Notice that the Generator Encoding Register bits [3:0] are set to 0b0011, as in the previous example. Bits [9:8] of the Generator Encoding Register is set to 1 instead of 0. This configures the Active Chroma output signal for 4:2:0 mode, but with the opposite line set.
The following C code shows how to configure the register values in Table: Example Vertical Generation Register Inputs (Alternate 4:2:0 Chroma) using the Video Timing Controller driver.
XVtc Vtc; /* Device driver instance */
XVtc_Signal SignalCfg; /* VTC Signal configuration */
XVtc_Polarity Polarity; /* Polarity configuration */
XVtc_SourceSelect SourceSelect;/* Source Selection configuration */
XVtc_Config *VtcCfgPtr;
VtcCfgPtr = XVtc_LookupConfig(VTC_DEVICE_ID);
XVtc_CfgInitialize(&Vtc, VtcCfgPtr, VtcCfgPtr->BaseAddress);
/* Setup the VTC Source Select config structure. */
/* 1=Generator registers are source */
/* 0=Detector registers are source */
memset((void *)&SourceSelect, 0, sizeof(SourceSelect));
SourceSelect.VBlankPolSrc = 1;
SourceSelect.VSyncPolSrc = 1;
SourceSelect.HBlankPolSrc = 1;
SourceSelect.HSyncPolSrc = 1;
SourceSelect.ActiveVideoPolSrc = 1;
SourceSelect.ActiveChromaPolSrc= 1;
SourceSelect.VChromaSrc = 1;
SourceSelect.VActiveSrc = 1;
SourceSelect.VBackPorchSrc = 1;
SourceSelect.VSyncSrc = 1;
SourceSelect.VFrontPorchSrc = 1;
SourceSelect.VTotalSrc = 1;
SourceSelect.HActiveSrc = 1;
SourceSelect.HBackPorchSrc = 1;
SourceSelect.HSyncSrc = 1;
SourceSelect.HFrontPorchSrc = 1;
SourceSelect.HTotalSrc = 1;
/* Setup the VTC Polarity config structure. */
memset((void *)&Polarity, 0, sizeof(Polarity));
Polarity.ActiveChromaPol = 1;
Polarity.ActiveVideoPol = 1;
Polarity.VBlankPol = 1;
Polarity.VSyncPol = 1;
Polarity.HBlankPol = 1;
Polarity.HSyncPol = 1;
/* Setup the VTC Signal config structure. */
memset((void *)&SignalCfg, 0, sizeof(XVtc_Signal));
SignalCfg.OriginMode = 1;//Set Frame Origin to Start of Active Video
SignalCfg.HTotal = 7;
SignalCfg.HActiveStart = 0;
SignalCfg.HFrontPorchStart = 3;// Active Video Width
SignalCfg.HSyncStart = 4;// Active Video Width + FP Width
SignalCfg.HBackPorchStart = 5;// Active Video Width + FP Width + Sync Width
SignalCfg.V0Total = 8;
SignalCfg.V0ChromaStart = 0;
SignalCfg.V0ActiveStart = 1;
SignalCfg.V0FrontPorchStart = 4;// Active Video Height
SignalCfg.V0SyncStart = 5;// Active Video Height + FP_Width
SignalCfg.V0BackPorchStart = 6;// Active Video Height + FP Width + Sync Width
/* Write VTC config to HW */
XVtc_RegUpdate(&VTC);
XVtc_SetPolarity(&Vtc, &Polarity);
XVtc_SetGenerator(&Vtc, &SignalCfg);
XVtc_SetSource(&Vtc, &SourceSelect);
XVtc_SetSkipLine(&Vtc, 1);
/* Enable VTC Generator */
XVtc_Enable Generator(&Vtc);