Variable-Size Mask Format for Multiprocessor Address Packets
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Solution Overview
Problem
In multiprocessor computer systems with shared memory architecture, the large address space and varying data sizes complicate communication protocols, leading to inefficient data access and transfer due to the need for extensive address bits in communication packets.
Innovation Solution
Implementing a variable-size mask format in address packets that includes a granularity field to indicate the size of data quantities, allowing for efficient selection of data without requiring all address bits, thereby reducing the packet size and improving communication efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If all address bits are included in communication packets to access large address space, then data access accuracy is improved, but packet size increases and communication efficiency decreases
Solution Approach 1:
The address field is segmented into two parts: a fixed-length base address field and a variable-length offset field. The base address is transmitted in all packets, while only the necessary offset bits are included in each packet based on the data size being accessed. This segmentation allows the system to maintain large address space capability while reducing the number of bits transmitted in each packet, thereby improving communication efficiency without sacrificing data access accuracy.
2Device complexity
If fixed-size mask format is used in address packets, then packet structure is simplified, but data access flexibility for varying data sizes is reduced
Solution Approach 1:
The mask field is designed with variable size rather than fixed size. The number of mask bits is dynamically adjusted based on the data size being accessed (e.g., 8 bits for bytes, 16 bits for words, 32 bits for doubles). This dynamic adjustment allows the same packet structure to accommodate different data sizes flexibly while maintaining a relatively simple overall structure, resolving the contradiction between structural simplicity and access flexibility.
3Productivity
If variable-size mask format with granularity field is implemented, then communication efficiency is improved by reducing packet size, but packet format complexity increases
Solution Approach 1:
The mask field serves multiple functions: it acts as both a data size indicator and an address offset selector. The granularity field indicates the size of data quantities (bytes, words, doubles) while the mask bits simultaneously select which specific data quantities to access. This multi-functionality reduces the need for separate fields, thereby improving communication efficiency while limiting the increase in packet format complexity to acceptable levels.
Data Source
AI summary
A system may include a device configured to initiate a transaction by sending an address packet and an additional device configured to respond to the address packet. The additional device is coupled to receive the address packet from the device via an address network. The address packet includes a mask field configured to indicate which of N quantities of data are targeted by the transaction. The address packet also includes a granularity field configured to indicate a size of each of the N quantities of data. If the size is less than a maximum size, a portion of the granularity field stores additional address bits of an address of the N quantities of data. If the size is the maximum size, none of the granularity field stores any additional address bits of the address of the N quantities of data.