Shared Package Pins in Multi-Chip Modules With Hardware Arbitration
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Solution Overview
Problem
In multi-chip modules, the mismatch between the number of I/O pads on dies and available package pins leads to inefficiencies, as not all I/O pads are connected to package pins, limiting accessibility for testing and debug functionality, which is crucial for error detection and correction.
Innovation Solution
Implementing a mechanism where multiple dies share package pins through an output enable register and arbitration circuitry, allowing a die to drive an output to shared package pins only when granted access, ensuring no simultaneous access by multiple dies and enabling increased I/O pad accessibility without increasing package pins.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If dedicated package pins are added to connect all I/O pads, then I/O pad accessibility is improved, but package size and complexity increase
Solution Approach 1:
Package pins are designed to serve multiple functions: they can be driven by different dies at different times for I/O operations, testing, and debug functionality. The arbitration circuitry enables a single package pin to be universally accessed by multiple dies through time-multiplexed control signals, eliminating the need for dedicated pins for each function.
Solution Approach 2:
Multiple die I/O pads that would traditionally require separate package pins are merged to share common package pins. The arbitration logic combines control signals from multiple dies to selectively enable one die at a time to drive its output through the shared package pin, reducing the total pin count while maintaining full accessibility.
2Ease of operation
If package pins are increased to provide dedicated I/O pathways, then I/O pad accessibility is improved, but package size increases
Solution Approach 1:
Package pins are designed to serve multiple functions: they can be driven by different dies at different times for I/O operations, testing, and debug functionality. The arbitration circuitry enables a single package pin to be universally accessed by multiple dies through time-multiplexed control signals, eliminating the need for dedicated pins for each function.
Solution Approach 2:
The solution moves from a spatial dimension (more pins for more access) to a temporal dimension (time-multiplexed access). By controlling which die can drive the package pin at any given time through arbitration logic and control signals, the system achieves full I/O pad accessibility without increasing the physical pin count or package footprint.
3Device complexity
If I/O bumps are not connected to package pins or are daisy chained, then package complexity is reduced, but observability of die data is lost
Solution Approach 1:
Arbitration circuitry acts as an intermediary between multiple dies and shared package pins. This intermediary component manages access requests from different dies, grants permission through control signals, and ensures that die data can be observed at the package level without requiring dedicated physical connections for each die.
Solution Approach 2:
The arbitration mechanism implements feedback control where dies send access requests to the arbitration logic, which responds with control signals that enable or disable package pin access. This feedback loop ensures that die data remains observable while preventing conflicts, as the arbitration logic continuously monitors and manages access permissions based on current package pin usage state.
4Device complexity
If multiple dies share package pins without arbitration, then package pin count is reduced, but simultaneous access errors occur
Solution Approach 1:
Arbitration circuitry acts as an intermediary between multiple dies and shared package pins. This intermediary component manages access requests from different dies, grants permission through control signals, and ensures that die data can be observed at the package level without requiring dedicated physical connections for each die.
Solution Approach 2:
The arbitration logic performs preliminary action by evaluating access requests and granting permission before actual data transfer occurs. Control signals are issued in advance to enable or disable package pin access for each die, preventing simultaneous access conflicts before they can occur and ensuring reliable operation of the shared pin infrastructure.
Data Source
AI summary
A semiconductor package includes multiple dies that share the same package pin. An output enable register provided on each die is used to select the die that drives an output to the shared pin. A hardware arbitration circuit ensures that two or more dies do not drive an output to the shared pin at the same time.