Speculative Command Decode Serial Interface for Access Time Reduction
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Solution Overview
Problem
In serial peripheral interface (SPI) systems, there is a challenge in reducing non-memory read access times to keep pace with decreasing memory read cycle times, as existing technologies struggle to quickly identify and respond to non-memory read commands within the rapidly decreasing cycle times, which can limit system performance.
Innovation Solution
A speculative command decode serial interface device that decodes high-order command bits to speculatively produce non-memory read commands, using a command decode register, data registers, an interface logic block, a data multiplexer, a data sequencer, and an output register to enable early identification and preparation of non-memory read data, allowing for faster response times without interfering with memory read command processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If traditional command decoding is used for non-memory read commands, then the system can process commands correctly, but the access time becomes too long and limits system performance
Solution Approach 1:
The patent applies preliminary action by speculatively decoding non-memory read commands before they are fully received. The command decode register decodes high-order command bits early in the cycle, and the interface logic block prepares data registers in advance. This allows the system to have the data ready before the complete command is received, significantly reducing access time and preventing non-memory read commands from becoming a performance bottleneck.
2Speed
If speculative decoding is implemented to reduce access time, then non-memory read response time improves, but the device complexity increases due to additional logic blocks and registers
Solution Approach 1:
The patent applies segmentation by dividing the command decoding process into distinct stages. The command decode register handles high-order bit decoding, while the interface logic block manages data register selection and control. This segmentation allows each component to be optimized independently and enables parallel processing of command decoding and data preparation, reducing overall access time despite increased device complexity.
Solution Approach 2:
The interface logic block performs preliminary actions by pre-selecting and preparing data in data registers before the complete command is received. This advance preparation reduces the critical path delay and allows faster response times, justifying the additional logic complexity required for speculative decoding.
3Loss of time
If early decoding of high-order command bits is performed, then the system can prepare responses faster, but there is a risk of incorrect decoding if the full command is not yet received
Solution Approach 1:
The patent applies partial action by decoding only the high-order bits of the command early in the cycle, rather than waiting for the complete command. This partial decoding is sufficient to identify non-memory read commands and prepare the appropriate data registers. The approach accepts some risk of premature decoding but mitigates it by using the decoded information only to prepare data, not to execute the full command until confirmation is received.
Data Source
AI summary
An apparatus and method of speculatively decoding non-memory read commands. A command register and decoder, within the apparatus, compares high-order command bits provided on a serial bus with corresponding bits of recognized non-memory read commands. An early non-memory read command is asserted when incoming command bits match a non-memory read command. Early responsive data is prepared speculatively during the time the remainder of command bits is received and decoded. A determination of command speculation correctness is made after receipt of the full command. If the full command received is not the speculated non-memory read command, the prepared data is discarded. Earlier prepared data is produced as the subsystem response if the full command matches the speculative non-memory read command. For incoming commands with operands, such as an address, the same speculative determination based on high-order operand bits is performed.