Simultaneous writes to the same address usually result in undefined data.ĭelta cycles are zero-time timesteps used by VHDL simulators for modeling chained events during code execution. While in simple dual-port RAM, one port is for reading and the other for writing, both ports can read and write in true dual-port RAM. True dual-port RAM means that both ports are interchangeable. Therefore, we can use each BRAM primitive individually to store data in our VHDL code. Block RAM is static RAM (SRAM), which doesn’t need refreshing. The CMOS technology in BRAM is different from the dynamic RAM (DRAM) used in regular computer memory. The image below shows the outline of a dual-port RAM from the Lattice iCE40 FPGA. The term “dual-port” means that it supports simultaneous reads and writes of any two addresses. It can be as little as 32 kbits (Lattice LP640) or as much as 94.5 Mbits (Xilinx VU13P).ĭual-port block RAM is the standard for modern FPGA architectures. The amount of block RAM varies greatly with the price of the FPGA. Usually, the chip provides rows or columns of BRAM distributed evenly throughout the floorplan, as shown in the example for the Lattice iCE40 device below. Block RAM (BRAM) is a type of on-chip random-access memory (RAM) found on most FPGAs.
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