2.3.2. DMA BBB
The DMA BBB subsystem transfers data from source to destination addresses using memory-mapped transactions. The DMA AFU accesses control and status registers in the DMA BBB subsystem. The DMA BBB comprises five IP cores available in the Platform Designer IP Catalog as shown in the following figure.
The components in the DMA BBB Platform Designer implement the following functions:
- Modular Scatter-Gather DMA (MSGDMA): This IP core performs memory mapped transfers between source and destination addresses. The MSGDMA transfers 64 bytes per clock cycle. The data must be aligned to 64-byte boundaries. The transfer length must be a multiple of 64 bytes. The MSGDMA supports 50-bit addressing and can transfer up to 16,777,152 bytes per descriptor. In this implementation, the driver limits the transfer size to 1,047,552 bytes per descriptor.
- Address Span Extender: This IP core implements memory transfers that are not aligned on a 64-byte boundary. The host uses it to perform MMIO accesses to FPGA device memory that are not aligned on a 64-byte boundary. The Address Span Extender accesses a 4 kilobyte (4 KB) window into the local device memory. The control port sets the base address of the (4 KB) window. The base address must be aligned to a 4 KB boundary so that the window is aligned to the window size. For example, to access FPGA memory address 0xF340, set the window address to 0xF000 and then access offset 0x0340 within the address span extender data window.
- BBB ID: This component stores the 64-bit Device Feature Header(DFH) and the UUID. The BBB_ID_L register stores the lower 32 bits of the BBB ID. The BBB_ID_H register stores the upper 32 bits of the BBB ID. A software driver scans the BBB ID to identify the functionality of this DMA subsystem.
- Magic Number ROM: This IP core contains a single, read-only 64-byte value. The DMA uses this value to create a write fence in host memory. This ROM is only visible to the MSGDMA. The host cannot access it.
- Pipeline Bridge: The Pipeline Bridge inserts pipeline stages to improve the system FMAX at the expense of latency.
Did you find the information on this page useful?