The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Oct. 05, 1993
Filed:
Dec. 30, 1991
Martin Sodos, San Jose, CA (US);
Sun Microsystems, Inc., Mountain View, CA (US);
Abstract
In the system of the present invention, the limitations imposed by the physical limitations of the DMA controller are overcome by storing the channel control blocks in external memory. The DMA controller is programmed to reference a particular address of external memory when a predetermined bit in the current channel control block is set. The DMA controller will then perform a memory read operation on the area of memory referred to by that address in order to store the retrieved channel control block at a location previously utilized by a earlier channel control block. This reading process will continue until the bit is reset, at which time the DMA operation is complete. Dynamic chaining is accommodated whereby the channel control blocks can be dynamically changed during the DMA access to provide a flexible I/O system. Furthermore, a method and apparatus for implementing dynamic chaining without incurring race conditions is described. A wait bit in each channel control block is provided when this bit is set, the DMA controller will suspend operations thereby providing opportunity for updating the chain of CCBs without incurring errors due to race conditions. Once the chain has been modified, the wait bit is reset and processing safely continues.