diff options
| -rw-r--r-- | README.md | 4 | ||||
| -rw-r--r-- | inc/cache.h | 26 | ||||
| -rw-r--r-- | src/cache.cc | 70 |
3 files changed, 71 insertions, 29 deletions
@@ -1,8 +1,6 @@ # RAM - RAM Acts Magically -## - -This is a cache and memory simulator for a custom ISA nicknamed "RISC V[ECTOR]". It uses a writeback and write allocate on a miss scheme, and supports a configurable number of cache levels and ways, with a least-recently used replacement policy. +This is a cache and memory simulator for a custom ISA nicknamed "RISC V[ECTOR]". It uses a writeback and write allocate on a miss scheme. It also supports a configurable number of cache levels and ways (allowing creation of a direct mapped or fully associative cache). Additionally, it uses a least-recently used replacement policy. ## Dependencies diff --git a/inc/cache.h b/inc/cache.h index 6f06466..8075d1a 100644 --- a/inc/cache.h +++ b/inc/cache.h @@ -55,7 +55,31 @@ nn * Constructor. * @param the address that must be present in cache. * @param 0 if the address is currently in cache, 1 if it is being fetched. */ - int is_address_missing(int address); + int priming_address(int address); + /** + * Walks the ways in this set of ways. If none of the tags match, returns -1. Otherwise, returns + * the index the matching data is located. + * @param an index aligned to the set of ways in `this->data' + * @param the tag to be matched + * @return -1 if the tag is not present in this set of ways (not in cache), or the true index if + * the tag is present. + */ + int is_address_missing(int true_index, int tag); + /** + * Converts an index into a set of ways into an index into `this->data', which is a + * 1D array. The next `this->ways' entries after the returned index represent the ways in the + * set for this index. + * @param an index to a set of ways + * @param an index aligned to the set of ways in `this->data' + */ + int get_true_index(int index); + /** + * Selects an index into the `data' and `meta' tables for write back using a random replacement + * policy. + * @param an index aligned to the set of ways in `this->data' + * @return an index aligned to the data line selected for eviction + */ + int get_replacement_index(int index); /** * The number of bits required to specify a line in this level of cache. */ diff --git a/src/cache.cc b/src/cache.cc index 08545fd..a2d4525 100644 --- a/src/cache.cc +++ b/src/cache.cc @@ -1,5 +1,6 @@ #include "cache.h" #include "definitions.h" +#include <cstdlib> #include <iostream> #include <iterator> @@ -61,53 +62,72 @@ Cache::read_word(void *id, int address, signed int &data) int Cache::process(void *id, int address, std::function<void(int index, int offset)> request_handler) { - if (!preprocess(id) || is_address_missing(address) || !this->is_data_ready()) + if (!preprocess(id) || priming_address(address) || !this->is_data_ready()) return 0; int tag, index, offset; GET_FIELDS(address, &tag, &index, &offset); + index = this->get_true_index(index); request_handler(index, offset); return 1; } int -Cache::is_address_missing(int expected) +Cache::priming_address(int address) { - int r, q, tag, index, offset; - std::array<signed int, LINE_SIZE> *actual; + int tag, index, offset; + int r1, r2; + std::array<signed int, LINE_SIZE> *evict; std::array<int, 3> *meta; - GET_FIELDS(expected, &tag, &index, &offset); - r = 0; - meta = &this->meta.at(index); - actual = &this->data->at(index); + r1 = 0; + GET_FIELDS(address, &tag, &index, &offset); + index = this->get_true_index(index); + + if (this->is_address_missing(index, tag)) { + r1 = 1; + + index = this->get_replacement_index(index); + meta = &this->meta.at(index); + evict = &this->data->at(index); - if (meta->at(0) != tag) { - r = 1; + // handle eviction of dirty cache lines if (meta->at(1) >= 0) { - q = this->lower->write_line( - this, *actual, ((index << LINE_SPEC) + (meta->at(0) << (this->size + LINE_SPEC)))); - if (q) { + r2 = this->lower->write_line( + this, *evict, ((index << LINE_SPEC) + (meta->at(0) << (this->size + LINE_SPEC)))); + if (r2) meta->at(1) = -1; - } } else { - q = this->lower->read_line(this, expected, *actual); - if (q) { + r2 = this->lower->read_line(this, address, *evict); + if (r2) { meta->at(0) = tag; } } } - return r; + return r1; +} + +int +Cache::is_address_missing(int index, int tag) +{ + int i; + + for (i = 0; i < (1 << this->ways); ++i) + if (this->meta.at(index + i).at(0) == tag) + return i; + return -1; } -// unsigned int -// Cache::get_true_index(unsigned int index) -// { -// } +int +Cache::get_true_index(int index) +{ + return index * (1 << this->ways); +} -// unsigned int -// Cache::get_replacement_index(unsigned int index) -// { -// } +int +Cache::get_replacement_index(int index) +{ + return index + (rand() % (1 << this->ways)); +} |