Difference between revisions of "MC System"

Revision as of 15:23, 17 May 2019

The many-core version of the project provides different type of tiles, although all share the same network- and coherence-related components. On the networking side, a generic tile of the system features a Network Interface module and a hardware Router, both described in Network architecture section.

The nu+ many-core features a shared-memory system, each nu+ core has a private L1 data cache, while the L2 cache is spread all over the instantiated tile along with a Directory Controller module which handles and stores coherence information for cached memory lines. Both are further described in Coherence architecture section.

NUPLUS tile

The NUPLUS tile mainly equips a nu+ GPGPU core, described in Nu+ GPGPU core section, and components used to interface the core with both networking and coherence systems. The following figure depicts a block view of the NUPLUS tile:

The tile implements a Cache controller, called l1d_cache, which interfaces the core to the memory system. The Cache controller exploits three Network interface virtual channels dedicated to the coherence system (ID 0 to 2), providing an abstracted view of the coherence to the core. For further details of the module and of the coherence system refer to Coherence architecture section. Two channels are also shared with the Directory controller.

Host communication, synchronization system and IO request leverage on the last Virtual Channel (ID 3) named Service Virtual Channel. The tile_nuplus module implements an arbiter which dispatches the incoming message from the service channel to the right module, based on the message_type field. E.g., a message from the host is marked as HOST and is forwarded to the boot manager module in the tile:

always @( ni_n2c_mes_service_valid, ni_n2c_mes_service, n2c_sync_message, bm_c2n_mes_service_consumed, sc_account_consumed, n2c_mes_service_consumed, io_intf_message_consumed ) begin
 ...
 if (ni_n2c_mes_service_valid) begin
   if( ni_n2c_mes_service.message_type == HOST ) begin
     bm_n2c_mes_service.data  = ni_n2c_mes_service.data;
     bm_n2c_mes_service_valid = ni_n2c_mes_service_valid;
     c2n_mes_service_consumed = bm_c2n_mes_service_consumed;
   end else if ( ni_n2c_mes_service.message_type == SYNC ) begin
      if ( n2c_sync_message.sync_type == ACCOUNT ) begin
        ni_account_mess          = n2c_sync_message.sync_mess.account_mess;
        ni_account_mess_valid    = ni_n2c_mes_service_valid;
        c2n_mes_service_consumed = sc_account_consumed;
   end else if ( n2c_sync_message.sync_type == RELEASE ) begin
        n2c_release_message      = n2c_sync_message.sync_mess.release_mess;
        n2c_release_valid        = ni_n2c_mes_service_valid;
        c2n_mes_service_consumed = n2c_mes_service_consumed;
   end
 ...

In case of SYNCH message, the above arbiter checks if the message is an ACCOUNT or a RELEASE type. In the first case, the service message is dispatched to the Synchronization core, otherwise to the nu+ core on the service interface, which is directly connected to the Barrier core module allocated in the core.

Possible incoming host requests are defined in the nuplus_message_service_define.sv header file:

typedef enum logic [`MESSAGE_TYPE_LENGTH - 1 : 0] {
 HOST  = 0,
 SYNC  = 1,
 IO_OP = 2
} service_message_type_t;

While Synchronization Core is widely described in the Synchronization architecture section, in the remains of this section we will focus on the other modules that rely on the Service Virtual Channel.

C2N Service Scheduler

This module stores and serializes requests from modules that attempt to send a message over the Service Virtual Channel. Since this channel has a single entry point, the c2n_service_scheduler provides a dedicated port to each of the requiring modules and forwards their request to the service virtual channel. When a conflict occurs, this module serializes the conflicting requests, each request is selected by an internal round-robin arbiter.

Boot Manager

Host commands are dispatched to the boot_manager module interconnected with the Thread Controller and control registers on the core. This module implements core-side logic for the item interface, described in theItem Interface section, interacting with the core on the basis of messages from the host.

IO Interface

The io_interface module fetches memory request on the non-coherent memory region and dispatches them to the right IO device allocated within the system. This module mainly converts a nu+ memory request into an IO message that will flow over the network. For each memory request from the core, the io_interface module encapsulates essential information, such as requesting address, in an IO message as follow:

assign io_intf_available_to_core = ~req_almost_full,
   req_value_i.io_source     = tile_id_t'(TILE_ID),    
   req_value_i.io_thread     = ldst_io_thread,
   req_value_i.io_operation  = io_operation_t'(ldst_io_operation),
   req_value_i.io_address    = ldst_io_address,
   req_value_i.io_data       = ldst_io_data;
    

IO messages from such a component are always forwarded to the H2C tile:

assign dest_tile_idx = issue_req ? `TILE_H2C_ID : saved_mess.io_source;

MC tile

The MC tile interfaces the main memory, which is defined as follow:

// To MANGO NI
output logic  [MANGO_ADDRESS_WIDTH - 1 : 0]             n2m_request_address,
output logic                       [63 : 0]             n2m_request_dirty_mask,
output logic  [MANGO_DATA_WIDTH - 1 : 0]                n2m_request_data,
output logic                                            n2m_request_read,
output logic                                            n2m_request_write,
output logic                                            n2m_request_is_instr,
output logic                                            n2m_avail,

// From MANGO NI
input  logic                                            m2n_request_read_available,
input  logic                                            m2n_request_write_available,
input  logic                                            m2n_response_valid,
input  logic  [MANGO_ADDRESS_WIDTH - 1 : 0]             m2n_response_address,
input  logic  [MANGO_DATA_WIDTH - 1 : 0]                m2n_response_data

The memory interface has a simple valid/available handshake and allows read/write operations.

The nuplus2mango module turns coherence messages from the nu+ core into valid memory requests for the interface above:

assign request_is_valid                = |request_oh & enable & ~pending_read;
assign request_is_read                 = request_is_valid & ( pending_fwd_request_out.packet_type == FWD_GETS | pending_fwd_request_out.packet_type == FWD_GETM ) & grant_oh[1];
assign request_is_write                = m2n_request_write_available & ni_response_network_available & ~pending_resp_fifo & request_is_valid & pending_response_out.packet_type == WB & grant_oh[0];

This module also provides endianness swapping supported if required:

if (SWAPEND) begin
 for ( swap_word = 0; swap_word < 16; swap_word++ ) begin : swap_word_gen
    assign m2n_response_data_swap[swap_word * 32 +: 8]      = m2n_response_data[swap_word * 32 + 24 +: 8];
    assign m2n_response_data_swap[swap_word * 32 + 8 +: 8]  = m2n_response_data[swap_word * 32 + 16 +: 8];
    assign m2n_response_data_swap[swap_word * 32 + 16 +: 8] = m2n_response_data[swap_word * 32 + 8 +: 8];
    assign m2n_response_data_swap[swap_word * 32 + 24 +: 8] = m2n_response_data[swap_word * 32 +: 8];

    assign out_data_swap[swap_word * 32 +: 8]               = pending_response_out.data[swap_word * 32 + 24 +: 8];
    assign out_data_swap[swap_word * 32 + 8 +: 8]           = pending_response_out.data[swap_word * 32 + 16 +: 8];
    assign out_data_swap[swap_word * 32 + 16 +: 8]          = pending_response_out.data[swap_word * 32 + 8 +: 8];
    assign out_data_swap[swap_word * 32 + 24 +: 8]          = pending_response_out.data[swap_word * 32 +: 8];
 end

Parameter SWAPEND determines whether the swapping logic is allocated or not.

H2C tile

The H2C tile interfaces the system with the host through the Item interface. The nuplus_item_iternface interprets incoming item from the host and builds service packets marked as HOST type which encapsulates the command sent by the host. One the packet is ready, the nuplus_item_interface forwards it to the destination tile through the service network. Section Item Interface details service packets sent by this module.

NONE tile

Empty tile, a NONE tile allocates only shared network- and coherence-related components.

HT tile

Described in Heterogeneous Tile section.