Controlling sdram memory by using truncated burst read-modify-write

Abstract

In a computer system having SDRAM memory banks that use a full burst read-modify-write operation as the sole mode for conducting memory operations, by selectively truncating the memory operation, it is possible to simulate either a burst read operation or a burst write operation. In a truncated read operation, a full read portion of the memory operation is performed. The tag is read with the first data line and is updated while the remaining lines of the burst are read. The tag is written using the write portion, but then the burst operation is aborted or truncated by issuing a precharge command to abort the write after the first line of the write is completed. This saves three clock periods out of a cycle of seventeen clock periods. A truncated write operation is similar to the read operation. A full burst read is started to retrieve the tag, which is stored to the first line, but the burst is truncated after the first line has been read. A full burst write operation is started immediately after the tag read, with the last lines of the data being written first. The tag data in the first line is being updated while the last three lines are being written. Then the cycle wraps around to write the first data line, including the tag, on the last cycle of the burst write.