Bull Hn Information Systems, Inc.

Bruce A Noyes

David A Egolf

Stefan R Bohult

George A Mann

Rene-Joseph Chevance

Chad Farmer

Russell Wayne Guenthner

A computer system includes a central processing unit, an addressable main memory storing data pages and a page table, and an associative memory. The associative memory stores a plurality of entries in accordance with a low order virtual address component issued by the CPU's processor when access to a given page in main memory is sought. Each entry in the associative memory includes fields respectively holding: 1) a high order virtual address component; 2) a real page address; and 3) a multi-digit validity count. An incrementable multi-digit counter in the CPU stores a current validity count. When access to a data page is sought, a comparator receives: 1) the high order virtual address component of the data page; 2) the high order virtual address component read from the associative memory entry; 3) the multi-digit validity count read from the associative memory entry; and 4) the multi-digit current validity count in the counter. If there is a full match, a switch issues the real page address read from the associative memory entry. If there is not a match, the page table is consulted to obtain the real address of the requested page, and the associative memory is updated accordingly.

Associative memory system with a multi-digit incrementable validity counter

Atomic multiple word reads are provided when emulating a target system that supports atomic multiple word reads on a host system that does not. For each except the last word to be read, a gate flag is read using an advanced speculative load, and tested, until found unlocked. Check speculation instructions are utilized after the gate flag tests to verify that the corresponding cache lines have not been invalidated through a write by another processor since the speculative loads were issued. In a host system with a longer word size than the target system, the gate flags can be stored in otherwise unused bits in the host system words containing the target system words to be written.

Method and data processing system for performing atomic multiple word reads

A host computer system, including an addressable main memory storing data pages and a page table, emulates a target computer system which includes an emulated target central processing unit, an emulated target associative memory and an emulated target multi-digit incrementable validity counter. The target associative memory stores a plurality of entries in accordance with a low order virtual address component issued by the target processor when access to a given page in main memory is sought. Each entry in the target associative memory includes fields respectively holding: 1) a high order virtual address component; 2) a real page address; and 3) a multi-digit validity count. The target multi-digit counter stores a current validity count. When access to a data page is sought, comparisons are made: 1) between the high order virtual address component of the data page and the high order virtual address component read from the target associative memory entry; and 2) between the multi-digit validity count read from the target associative memory entry and the multi-digit current validity count in the target counter. If there is a full match, the real page address of the requested page is read from the target associative memory entry. If there is not a match, the page table is consulted to obtain the real address of the requested page, and the target associative memory is updated accordingly.

Emulated target associative memory system with a multi-digit incrementable validity counter

In an emulation of a multiprocessor Target computer system on a Host computer system, Host virtual memory addresses are mapped and utilized as Target virtual memory addresses. Target virtual memory control tables are setup accordingly. Each Target processor is mapped to a Host thread. When a page fault is detected by the Host operating system, it is checked to see if it belongs to the Target system, and if it does, the executing thread transfers its processor identity to a free thread, and then completes processing the page fault. Upon completion, it marks the processes that had been executing on that thread and processor as available for execution, then blocks until activated. Another thread, upon dispatching that process, wakes up the blocked thread and transfers its processor identity to that thread, which continues to execute the interrupted process.

Method and data processing system for emulating virtual memory utilizing threads

Atomic multiple word writes are provided when emulating a target system that supports atomic multiple word writes on a host system that does not. For each except the last word to be written, a gate flag is read, tested, and locked when it is found unlocked. The words are then written to memory in reverse order, unlocking the gate flags as they are written. In a host system with a longer word size than the target system, the gate flags can be stored in otherwise unused bits in the host system words containing the target system words to be written.

Method and data processing system for performing atomic multiple word writes

In a data processing system implementing Dynamic Object Code Translation (DOCT) for emulating Target system instructions on a Host system, each Target system instruction has an associated index/offset field and an associated code tag that identifies whether the Target instruction has been translated into Host code, and if already translated, whether it is an entry point, middle, or last instruction in a block of code. When an emulator encounters a code tag indicating an entry point into a block of code, execution control is transferred to the corresponding Host code. Upon completion of the Host code block, execution control is returned to the emulator, with an indication of the next Target system instruction to execute. One code tag value is utilized to identify self-modified code. Another code tag value is utilized to indicate how often untranslated Target instructions have been interpreted in order to determine when to perform DOCT.

Method and apparatus for dynamic management of translated code blocks in dynamic object code translation

Method and apparatus for emulating self-modifying code

In an emulation of a multiprocessor Target computer system on a Host computer system, Host virtual memory addresses are mapped and utilized as Target virtual memory addresses. Target virtual memory control tables are setup accordingly. Virtual-to-real address translation of a Target system effective address to a Host system virtual addresses is performed by identifying a working space for the effective address, determining a working space base address for that working space, and then performing a linear translation multiplying the effective address by a constant and adding it to the working space base address to generate the host system virtual address.

Method and data processing system for emulating virtual memory working spaces

Storage structure for dynamic management of translated code blocks in dynamic object code translation

In an emulation of a multiprocessor Target computer system on a Host computer system, Host virtual memory addresses are mapped and utilized as Target virtual memory addresses. Target virtual memory control tables are setup accordingly. Virtual-to-real address translation of a Target system effective address to a Host system virtual addresses is performed by identifying a working space for the effective address, selecting a working space base address data structure entry utilizing the corresponding working space number, determining a working space base address from that selected working space base address data structure entry, and then performing a linear translation multiplying the effective address by a constant and adding it to the working space base address to generate the host system virtual address. A corresponding working space limit entry can be utilized to bounds check the addresses generated.

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Phoenix, AZ, United States of America

Bruce A Noyes