The DirectMappedCache repo contains files for a computer architecture project to implement a 256-byte Direct mapped cache with 8 byte long cache lines. The cache is byte-addressable, and follows a write-back write policy and a write-allocate write miss policy.
Input: A text file containing a column of 32-bit hexadecimal numbers stored as strings, e.g.
36D2 FF C2
FC33 00 0B
...
The individual bits of the hexadecimal string contains data to be stored in cache, and instructions on how to store the data in cache, and in main memory during a
write-miss / read-miss eviction. These instructions are the tag, address (offset, and line number), and the read/write indicator: 0x00 = read, 0xFF = write.
For example, extracting these features for one line 36D2 FF C2 is done as follows:
tag: Is the first leftmost 8-bits in the 32-bit hexadecimal number: 36.
data : Is the last rightmost 8-bits in the 32-bit hexadecimal number: C2.
read/write operation: 8-bits in the middle of the 32-bit hexadecimal number: FF => write to cache.
address : The next 8-bits after the tag, D2.
The address is paritioned into an offset and line number. The address assigns values to offset and line number depending on the memory size of the cacheline and number of cachelines, respectively.
In this case, the offset requires 3-bits since the cacheline is 8 bytes, and would need only log_2(8) = 3 bits for addressing.
The line number requires the remaining 5-bits. There are 32 cachelines, so 5-bits are necessary for addressing.
Example:
D2 = 11010010, which means offset = 010 = 2, and line number = 11010 = 26. So given a write operation, the program stores data in line number 26, inside line number 26's memory block at index 2.
Note: When a read operation is performed, the data contained in the hexadecimal string is ignored.
Output: A text file named dm-out.txt. Each line of dm-out.txt corresponds to the results of each read operation peformed on the cache. The lines are formatted as follows:
D2 0 1
The information is, in order, the data returned from the read operation (in hexadecimal), a 'hit' output (1 or 0) that indicates whether or not the requested item was found in cache, and the dirty-bit (1 or 0) which indicates whether or not a memory block in cache was modified.
Requires C++11 or greater to compile. Open command prompt, enter the directory containing this repo, and type the following to complie the project:
g++ -std=c++11 DirectMappedCache.h DirectMappedCache.cpp dmcache2.cpp
Next, use run the resulting a.out executable with one of the test files. E.g.,
./a.out test-file.txt
This will output dm-out.txt into the current directory.