External Memory Interface Configuration via Stored Data Word
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Solution Overview
Problem
Data processing devices face challenges in determining the external memory size and Endian form without dedicated selection pins, leading to increased costs and implementation complexities, especially in battery-powered equipment where leakage currents are a concern.
Innovation Solution
A data processing device that stores an N-bit data word representing its size and Endian form in external memory, using a configuration means to deduce this information and set the external memory interface width and processor mode accordingly, eliminating the need for dedicated selection pins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If dedicated selection pins are used to indicate external memory configuration, then the embedded logic can determine memory size and Endian form, but the number of pins increases and package size increases
Solution Approach 1:
The external memory is used for dual purposes: storing the program code and storing the configuration data (memory size and Endian form indicators). This eliminates the need for dedicated selection pins by making the memory serve multiple functions.
Solution Approach 2:
Instead of using physical pins to convey configuration information, the configuration data is copied into the external memory at specific addresses. The embedded logic then reads this copied data to determine the memory configuration, replacing physical pin signals with data storage.
2Device complexity
If selection pins are shared and their state is latched during start-up phase, then the number of pins is reduced, but pull-up or pull-down resistors are required which create leakage current
Solution Approach 1:
The mechanical/electrical system of pull-up or pull-down resistors is replaced with a software-based configuration data storage approach. The memory itself stores the configuration state, eliminating the need for passive components that consume power.
Solution Approach 2:
The external memory automatically retains the configuration data (memory size and Endian form) without requiring external components to maintain its state. The memory serves itself by storing the configuration information that the embedded logic reads during initialization.
3Loss of energy
If more complex pin sharing solutions are implemented, then leakage current is reduced, but implementation difficulties increase
Solution Approach 1:
The configuration information is copied into the external memory at predetermined addresses during memory programming. This simple data copying approach replaces complex hardware sharing schemes, making the implementation easier while avoiding leakage current issues.
Solution Approach 2:
The configuration is represented as changeable data parameters stored in memory rather than fixed hardware connections. This allows flexible configuration (different memory sizes and Endian forms) to be achieved by changing the data content rather than redesigning the hardware connection scheme.
Data Source
AI summary
A data processing device (D) comprises an external memory (EM) for storing data defining at least part of a program in an Endian form, and an integrated circuit (IC), connected to the external memory (EM), via a memory bus (MB) having an N-bit width, and comprising i) an embedded processor (EP) adapted to run the program, ii) an internal memory (IM) for storing at least a bootstrap code of this program, iii) an external memory interface (EMI) connected to the memory bus (MB), and iv) a processor bus (PB) connecting the internal memory (IM) and the external memory interface (EMI) to the embedded processor (EP). The external memory (EM) also stores, at a chosen address, an N-bit data word (C) having a value representative of its size (equal to N/8 bits) and of the Endian form of the stored program data. The data processing device (D) also comprises a configuration means (CM) coupled to the embedded processor (EP) and to the external memory interface (EMI) and arranged to deduce from at least one part of 8 bits of this N-bit data word (C), read by the external memory interface at the chosen address of the external memory (EM), the size and the Endian form of storage of the external memory, and to set the width of the external memory interface (EMI) according to the deduced external memory size and the data processing mode of the embedded processor (EP) according to the deduced Endian form of storage.