DM816x and GS2971 connection
Introduction
The goal of this article is to provide some small tips about connecting the GS2971 SDI receiver to the DM816x Video Input Ports (VIP) in order to avoid problems during the hardware bring up stage of your board. Connecting the GS2971 in the wrong way will cause a problem in the color space giving as result images with weird colors.
Connection
The GS2971 is an SDI receiver that is able to output 10bit or 20bits to represent each of the pixels, this can be select through the pin number H7 which corresponds to the control signal pin called 20bit/10bit (HIGH=20, LOW=10). There are several control signal pins present in the GS2971 as you can see in the datasheet, these are normally controlled through i2c using one I/O expander like the PC8575 or using an FPGA.
The GS2971 configuration is done through SPI and RidgeRun already has available the linux driver for the chip so this part is not covered on this article. The main problems about the GS2971 and the DM816x are related about how to connect a 20bits BT1120 interface with the 8/16/24 VIPs present in the DM816x. According to the DM816x technical reference manual the VIP capabilities are:
12.10.1 VIP Features Features of the VIP include: • Input – YUV422 8-bit embedded sync mode (exclude BT. 1120) – YUV422 8-bit discrete sync mode – YUV422 16-bit embedded sync mode – YUV422 16-bit discrete sync mode – YUV422 8-bit 2x/4x pixel multiplexed mode – YUV422 8-bit 4x line multiplexed mode – RGB 24-bit embedded sync mode – RGB 24-bit discrete sync mode – YUV444 24-bit embedded sync – YUV444 24-bit discrete sync mode
The GS2971 can generate the timing reference signals (TRS) as embedded signals in the data stream or it can be configured to use discrete sync signals, i.e, dedicated pins to control the synchronization. RidgeRun recommends to configure the GS2971 to output 20bits (10bits chroma Cb/Cr + 10bit luma Y) with embedded sync signals in order to use the DM816x VIP in 16bits mode with embedded sync signals to capture frames. On this case the two less significant bits of each 10bits word needs to be ignored. Please see Figure 1.
In case of a wrong connection the image would look with wrong colors:
while using the good connection the image captured by the VPSS looks like Figure 3.
