The memory hierarchy communicates by sending memory requests and answers. The memory request data type is used to send those request and answer messages. The modules usually sending request are the cpu module and the cache module on a miss, and the module sending answers are the memory and the cache on a hit.

Note that a memory request signal can either be a memory request (not answered yet) or the answer of such a request.

The memory request signal is declared as the memreq class defined in the memreq.h file in the repository. : better link

• typename INSTRUCTION
  The type used to store the instruction corresponding to each message. This information is not used to deal with memory request, but is very useful for debugging purpose as it allows to point out the instruction from which the request comes from.
• int DATASIZE
  The datasize is the maximum size in bytes of data that can be stored in a memory request. This data field is only used for memory answers.

• ByteArray<DATASIZE> data
  The data embedded in memory request answers.
• INSTRUCTION instr
  The processor instruction that is responsible of the existence of this message. Only used for debugging purpose.
• uint32_t address
  The memory address corresponding to the request or to the answer.
• int size
  The size of the retrieved data in bytes.
• command_t command
  The type of the memory request (READ, WRITE, ...).
• int uid
  The unique ID of the incoming instruction.
• sender_type_t sender_type
  The type of the sender (CPU, CACHE, MEMORY, ...).
• message_type_t message_type
  The type of the message (Request, Answer).
• module *sender
  A pointer to the module that has sent this message.
• module *req_sender
  A pointer to the module that has sent the original request corresponding to this message.
• bool cachable
  Whether or not the request address is cachable. This modify the way the request is handled by caches.

The enum command_t provides some information about the command of the message (read, write, prefetch, \dots). The possible values are:

• cmd_UNKNOWN
  The request command is unset. New messages are initialized to this value. Sent messages should no more be set to this value.
• cmd_READ
  The request command is a read. Such request are issued by the \emph{cpu} and the \emph{caches} on a miss, and answered by \emph{caches} and \emph{memory}.
• cmd_READX
  The request command is a read with intent to modify. Such request are issued by \emph{caches} on a write miss that first requires to perform a read of the corresponding cache line before writing in the line itself.
• cmd_WRITE
  The request command is a write. Such request are issued by the \emph{cpu}, also by \emph{caches} on a write-back to memory. Such request are not answered.
• cmd_PREFETCH
  The request command is a prefetch read. Such request are issued by the \emph{cpu}. The connected caches then perform a \emph{read} to the memory hierarchy.
• cmd_EVICT
  This request perform an eviction of a cache line, forcing a write-back to the memory.
• cmd_FLUSH
  This request flush a cache line, performing a write-back to the memory hierarchy if the line is \emph{dirty}.
• cmd_BLOCK_INVALIDATE
  This request perform a block invalidate request.

The enum sender_type_t provides some information about the sender of the message. Possible values are:

• sender_UNKNOWN
  The sender type is unset. New messages are initialized to this value. Sent messages should no more be set to this value.
• sender_CPU
  The message is issued by a \emph{cpu}. Such messages should be requests sent to the memory hierarchy.
• sender_CACHE
  The message is issued by a \emph{cache}. Such messages can be a request sent to the memory hierarchy, or an answer sent back to the \emph{cpu}.
• sender_MEM
  The message is issued by a main \emph{memory}. Such messages should be answers from the memory to a previously sent requests.

The enum message_type_t provides some information about the message type (request or answers). The possible values are:

• type_UNKNOWN
  The message type is unset. New messages are initialized to this value. Sent messages should no more be set to this value.
• type_REQUEST
  The message type is a request, so it contains no data, and will eventually be replyed by an answer.
• type_ANSWER
  The message type is an answer so it contains the data answering to a previously sent request.