SPRUIE9D May 2017 – May 2024 DRA74P , DRA75P , DRA76P , DRA77P
The DMA synchronization line, DISPC_DREQ, is connected to the device DMA controllers (see Table 13-59, DMA Requests). This DMA request is not a classical one, but rather a synchronization signal between the DISPC and device DMA. The device DMA is informed that a programmable number of lines are output to the LCD and that a system memory can be updated. This request is related to the interrupt event PROGRAMMEDLINENUMBER_IRQ described in Table 13-60. This allows the device DMA channel to be synchronized with the internal DMA controller in the display subsystem.
In other words, it allows synchronizing a memory-to-memory frame buffer update based on the scan line of the frame buffer in system memory (SDRAM or SRAM) by the DISPC. The DISPC_DREQ request is generated at a programmable line number defined in the DISPC_LINE_NUMBER[11:0] LINENUMBER bit field. This process allows an application to use a single frame buffer and to update it after a certain number of lines are read by the DISPC.