Intel® Quartus® Prime Standard Edition User Guide: Design Recommendations

ID 683323
Date 9/24/2018
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1.5. Implementing Embedded RAM

Intel’s dedicated memory architecture offers many advanced features that you can enable with Intel-provided IP cores. Use synchronous memory blocks for your design, so that the blocks can be mapped directly into the device dedicated memory blocks.

You can use single-port, dual-port, or three-port RAM with a single- or dual-clocking method. You should not infer the asynchronous memory logic as a memory block or place the asynchronous memory logic in the dedicated memory block, but implement the asynchronous memory logic in regular logic cells.

Intel memory blocks have different read-during-write behaviors, depending on the targeted device family, memory mode, and block type. Read-during-write behavior refers to read and write from the same memory address in the same clock cycle; for example, you read from the same address to which you write in the same clock cycle.

You should check how you specify the memory in your HDL code when you use read-during-write behavior. The HDL code that describes the read returns either the old data stored at the memory location, or the new data being written to the memory location.

In some cases, when the device architecture cannot implement the memory behavior described in your HDL code, the memory block is not mapped to the dedicated RAM blocks, or the memory block is implemented using extra logic in addition to the dedicated RAM block. Implement the read-during-write behavior using single-port RAM in Arria GX devices and the Cyclone and Stratix series of devices to avoid this extra logic implementation.

In many synthesis tools, you can specify that the read-during-write behavior is not important to your design; if, for example, you never read and write from the same address in the same clock cycle. For Intel® Quartus® Prime integrated synthesis, add the synthesis attribute ramstyle=”no_rw_check” to allow the software to choose the read-during-write behavior of a RAM, rather than using the read-during-write behavior specified in your HDL code. Using this type of attribute prevents the synthesis tool from using extra logic to implement the memory block and, in some cases, can allow memory inference when it would otherwise be impossible.