Follow these step-by-step instructions to understand and explore the MSI Cache Coherence Protocol using the interactive simulator.

Step 1: Understanding the Interface

1. Observe the Initial State

   • Notice that both processor caches start with all cache lines in the Invalid (I) state
   • The state diagrams show the current state of each processor's cache
   • The transaction log is initially empty

2. Familiarize with the Components

   • Cache State Diagrams: Visual representation of MSI states (M, S, I) for each processor
   • Simulation Controls: Interface to select processor, operation type, address, and data
   • Processor Cache States: Table showing the detailed state of each cache line
   • Bus Transaction Log: Historical record of all operations and state transitions

Step 2: Basic Read Operations

1. First Read Operation

   • Select Processor 0 from the dropdown
   • Choose PrRd (Processor Read) as the operation type
   • Select memory address 0x0
   • Click "Execute Operation"

2. Observe the Results

   • Cache line at index 0 in Processor 0 transitions from I → S
   • Bus activity shows BusRd transaction
   • Data is loaded from memory into the cache
   • Note the cache miss recorded in performance statistics

3. Repeat with Second Processor

   • Select Processor 1
   • Perform the same read operation on address 0x0
   • Observe that Processor 1 also gets the data in Shared (S) state
   • Both processors now have the same data in Shared state

Step 3: Write Operations and Invalidations

1. Write to Shared Data

   • Keep Processor 1 selected
   • Change operation to PrWr (Processor Write)
   • Select address 0x0 (same as previous reads)
   • Enter a data value (e.g., "42") in the data field
   • Click "Execute Operation"

2. Analyze State Changes

   • Processor 1's cache line transitions from S → M
   • Processor 0's cache line transitions from S → I (invalidated)
   • Bus activity shows BusUpgr transaction
   • Only Processor 1 now has valid data for this address

Step 4: Modified State Operations

1. Read from Modified Cache

   • With Processor 1 still selected
   • Change back to PrRd (Processor Read)
   • Read from address 0x0
   • Observe that this is a cache hit and state remains Modified (M)

2. Write to Modified Cache

   • Change to PrWr (Processor Write)
   • Enter a new data value (e.g., "100")
   • Write to address 0x0
   • Notice this is also a cache hit with no bus activity needed

Step 5: Cache Line Sharing After Modification

1. Another Processor Reads Modified Data

   • Select Processor 0
   • Choose PrRd (Processor Read)
   • Read from address 0x0 (which Processor 1 has modified)
   • Click "Execute Operation"

2. Observe Write-Back and Sharing

   • Processor 1's cache transitions from M → S
   • Processor 0's cache transitions from I → S
   • Data is written back to memory and shared
   • Both processors now have consistent data in Shared state

Step 6: Exploring Different Addresses

1. Access Different Memory Locations

   • Try operations on addresses 0x1, 0x2, and 0x3
   • Observe how different cache lines are affected
   • Notice that cache coherence operates independently for each cache line

2. Create Complex Scenarios

   • Mix read and write operations across different processors
   • Try patterns like: P0 writes to 0x0, P1 writes to 0x1, then cross-access
   • Observe how cache performance metrics change

Step 7: Performance Analysis

1. Monitor Cache Performance

   • Pay attention to the hit/miss ratios for each processor
   • Notice how coherence protocol overhead affects performance
   • Compare performance for read-only vs. read-write workloads

2. Analyze Transaction Patterns

   • Study the bus transaction log to understand communication overhead
   • Identify patterns in state transitions
   • Observe the relationship between processor operations and bus activities

Step 8: Advanced Scenarios

1. False Sharing Simulation

   • Have both processors write to different addresses that map to the same cache line
   • Observe unnecessary invalidations due to spatial locality

2. Producer-Consumer Pattern

   • Simulate one processor writing data (producer)
   • Have the other processor read the data (consumer)
   • Observe the coherence protocol maintaining consistency

Expected Learning Outcomes

After completing this procedure, you should understand:

• How the MSI protocol maintains cache coherence across multiple processors
• The relationship between processor operations, bus transactions, and state transitions
• Performance implications of different access patterns in shared-memory systems
• The trade-offs between cache performance and coherence overhead
• Real-world applications of cache coherence protocols in multicore systems

Troubleshooting Tips

• If no changes occur, ensure you've clicked "Execute Operation"
• Remember that data values are only required for write operations
• Use the transaction log to trace the history of operations
• Reset the simulation by refreshing the page if needed