The Blue Genet/L compute (BLC) and Blue Gene/L link (BLL) chips have extensive facilities for control, bring-up, self-test, debug, and nonintrusive performance monitoring built on a serial interface compliant with IEEE Standard 1149.1. Both the BLL and the BLC chips contain a standard eServere chip JTAG controller called the access macro. For BLC, the capabilities of the access macro were extended 1) to accommodate the secondary JTAG controllers built into embedded PowerPC t cores; 2) to provide direct access to memory for initial boot code load and for messaging between the service node and the BLC chip; 3) to provide nonintrusive access to device control registers; and 4) to provide a suite of chip configuration and control registers. The BLC clock tree structure is described. It accommodates both functional requirements and requirements for enabling multiple built-in self-test domains, differentiated both by frequency and functionality. The chip features a debug port that allows observation of critical chip signals at full speed. * Trademark or registered trademark of International Business Machines Corporation.
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