Fullword Even Branch
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2005-Feb-02
Described is a Fullword Even branch in a processor wherein microcode can determine which half of a doubleword storage data register contains the first byte of data. Normally, when HMC (Horizontal Microcode) fetches from memory, an "aligned doubleword fetch" is performed. The low 3 bits of the address provided by HMC (which specify a particular byte within the doubleword) are not sent to the memory. Thus the first byte of arbitrarily aligned data may be in either the left or the right fullword of the storage data register. In order to assist in fetching objects which may cross a double- word boundary, the processor has an "unaligned doubleword fetch" capability. If the address of the data to be fetched is in the left fullword of a doubleword (an "Even fullword"), then the hardware performs a double word fetch from memory.