Command Stacking For Microprocessor Controlled Channel Interface
Original Publication Date: 1982-Mar-01
Included in the Prior Art Database: 2005-Feb-09
In Fig. 1, I/O controller (IOC) 20 controls more than one I/O device or operational unit (OU) 30. In the computer system shown in Fig. 1 there is no control unit busy response. The system is architected in a manner where it is assumed that IOC 20 will accept a command within a predetermined period of time. A problem arises with this architectural arrangement because IOC 20 may be busy with a command to one device 30 and be unable to handle another command to another device 30. Channel 15 normally waits for a response from IOC 20, but after waiting the predetermined time for the response and there is no response, it logs a time out error. In order to avoid this time out error and still be able to handle commands for more than one OU attached to the single IOC 20, channel bus 16 (Fig.