ESYNet User Manual : Simulation Engine

• Event-driven Simulation
• Events in Esynet
• Event Handler Flow
• HOW TO

ESYNet utilizes an event-driven simulation engine to perform the cycle-accurate simulation.

graph TD
A-->B

Loading

Event-driven Simulation

The event-driven simulator consists of a simulation engine and simulation components. Simulation engine drives the simulation process forward while simulation components store the status and do the operations. In ESYNet, simulation components include routers and network interfaces.

The kernel of the simulation engine is the event queue which stores the events in the order of increasing time. The event is an abstraction of simulation operations. The time determines when the simulation engine should respond to the specified event.

During the simulation, the simulation engine takes out the first event in the event queue and calls corresponding simulation components to respond to the event. Simulation components receive the event and perform the correct function. After that, simulation components generate new events if necessary. The new events are inserted back to the event queue.

The simulation engine continues the iteration until all the events in the event queue have been responded. Thus, if the event queue is empty, the simulation is finished. When the simulation starts, the first event should be inserted to the event queue so that the simulation can start. The simulation stops if the event queue is empty.

The simulation time depends on the number of events. For example, if the NoC is not under heavy traffic, the simulation time can be very fast because there is not much event. On the other hand, the simulation accuracy depends on the fine-grain of event definitions.

ESYNet provides EsynetEventQueue as the event queue. Event queue inherits from STL multiset so that it can automatically sort items within the event queue. The key is the time when to pop the event from the queue.

ESYNet provides EsynetSimBaseUnit as the base-class for simulation components. The simulation components must inherit from EsynetSimBaseUnit. Otherwise, they cannot be called by the event queue. Currently, ESYNet provides three simulation components:

• EsynetFoundation: Network platform, includes all routers and NIs.
• EsynetRouter: Router structure.
• EsynetNI: NI structure.

During the simulation, EsynetEventQueue pops the first event from the event queue. Then, EsynetEventQueue calls EsynetFoundation to response this event. EsynetFoundation distinguishes the type of the event and calls a corresponding router or NI to respond to the event. Further, EsynetRouter and EsynetNI perform the function related to the event. When handle event, simulation components may generate new events. These new events are collected and injected into the event queue as well.

Events in Esynet

ESYNet provides EsynetEvent to store the information for different events.

Packet generation event

Packet generation event (EVG) means a new packet should be injected into the network. The traffic generator or integration APIs generate EVG events.

EsynetEvent provides EsynetEvent::generateEvgEvent to generate a EVG event. EVG event should provides the following information.

Fields	Data type	Note
EsynetEvent::m_event_time	double	The injection time of the packet.
EsynetEvent::m_event_type	long	EsynetEvent::EVG.
EsynetEvent::m_src_id	long	Source router id.
EsynetEvent::m_des_id	long	Destination router id.
EsynetEvent::m_flit	EsynetFlit	The head flit of new packet.

EsynetEvent::m_flit should provide the following information.

Fields	Data type	Note
EsynetFlit::m_id	long	Packet id.
EsynetFlit::m_pac_size	long	Packet size in flit.
EsynetFlit::m_type	FlitType	EsynetFlit::FLIT_HEAD.
EsynetFlit::m_src_ni	long	Source router id.
EsynetFlit::m_des_ni	long	Destination router id.
EsynetFlit::m_flag	uint16_t	Flit flags.
EsynetFlit::m_flit_start_time	double	The injection time of the packet.

EsynetFoundation provides EsynetFoundation::receiveEvgMessage method to handle EVG event. The network platform calls the NI specified by EsynetEvent::m_des_id to respond EVG event. NI generates all the flits for the packets and stores flits in the injection queue. See also Traffic generation for more information.

Router pipeline

Router pipeline event (ROUTER) means one clock cycle for the pipeline in the router. ROUTER event provides the ability for ESYNet to perform the cycle-accuracy simulation. The simulation engine itself generates ROUTER events.

EsynetEvent provides EsynetEvent::generateRouterEvent to generate a ROUTER event. ROUTER event should provide the following information.

Fields	Data type	Note
EsynetEvent::m_event_time	double	The simulation cycle.
EsynetEvent::m_pipe_time	double	The period of the pipeline in cycle.
EsynetEvent::m_event_type	long	EsynetEvent::ROUTER.
EsynetEvent::m_src_id	long	Specified router to respond this event. Default value is -1.

ROUTER event is the first event in the event queue. When initializing the event queue, the event queue injects the first ROUTER event.

EsynetFoundation provides EsynetFoundation::receiveRouterMessage method to handle ROUTER event. During the simulation, the network platform generates the next ROUTER event when it responds to one ROUTER event. The simulation cycle of the next ROUTER is calculated by added EsynetEvent::m_pipe_time to EsynetEvent::m_event_time. By default, the network platform calls all the routers and NIs to respond ROUTER event. Each router and NI does the pipeline once when they receive ROUTER event. See also Router pipeline and NI pipeline for more information.

ESYNet can support multi-clock-domains in NoC, which means simulation components may not respond ROUTER event at the same time. The basic clock period is 1.0 cycle. One ROUTER event with EsynetEvent::m_pipe_time as 1.0 can trigger all routers and NIs within the base clock domain. Another clock period is measured by the basic clock period. One ROUTER event with EsynetEvent::m_pipe_time not as 1.0 can only trigger the router and NI specified by EsynetEvent::m_src_id.

The network platform also calls traffic generator in ROUTER events. The traffic generator is only called by the ROUTER event with EsynetEvent::m_pipe_time as 1.0. See also Traffic generation for more information.

Link transmission event

Link transmission event (WIRE) means a flit transmits through one link. WIRE events are generated by the link transmission stage in router pipeline.

EsynetEvent provides EsynetEvent::generateWireEvent to generate a WIRE event. One WIRE event means EsynetEvent::m_flit transmits from EsynetEvent::m_src_vc of EsynetEvent::m_src_pc of EsynetEvent::m_src_id to EsynetEvent::m_des_vc of EsynetEvent::m_des_pc of EsynetEvent::m_des_id at EsynetEvent::m_event_time. WIRE event should provides the following information.

Fields	Data type	Note
EsynetEvent::m_event_time	double	The time when the flit should be received by the destination router.
EsynetEvent::m_event_type	long	EsynetEvent::WIRE.
EsynetEvent::m_src_id	long	Source router.
EsynetEvent::m_src_pc	long	Output physical port of source router.
EsynetEvent::m_src_vc	long	Output virtual channel of source router.
EsynetEvent::m_des_id	long	Destination router.
EsynetEvent::m_des_pc	long	Input physical port of destination router.
EsynetEvent::m_des_vc	long	Input virtual channel of destination router.
EsynetEvent::m_flit	EsynetFlit	The transmitted packet.

EsynetFoundation provides EsynetFoundation::receiveWireMessage method to handle WIRE event. The network platform calls the router or NI specified by EsynetEvent::m_des_id to respond WIRE event. See also Receive flit in the router and [Receive flit in NI] for more information. The network platform also calls the router or NI specified by EsynetEvent::m_src_id to clear the status of the link.

The source and destination id encode the routers and NIs in the same field. The lower part of the value is used to specified routers; the higher part of the value is used to specified NI. For example, for an 8x8 regular mesh topology, 0-63 is used to label routers; 64-127 is used to label NIs.

Credit transmission event

Credit transmission event (CREDIT) means a credit value transmits through one link. The credit means the number of free slots in the virtual channels of the input channels connected with the virtual channels of the output channels. In credit-based flow control, the credit is transmitted by the wires between routers as well. The CREDIT events are generated by the router pipeline as well. See [flow control] for more information.

EsynetEvent provides EsynetEvent::generateCreditEvent to generate a CREDIT event. CREDIT event should provides the following information.

Fields	Data type	Note
EsynetEvent::m_event_time	double	The time when the flit should be received by destination router.
EsynetEvent::m_event_type	long	EsynetEvent::CREDIT.
EsynetEvent::m_src_id	long	Source router.
EsynetEvent::m_src_pc	long	Input physical port of source router.
EsynetEvent::m_src_vc	long	Input virtual channel of source router.
EsynetEvent::m_des_id	long	Destination router.
EsynetEvent::m_des_pc	long	Output physical port of destination router.
EsynetEvent::m_des_vc	long	Output virtual channel of destination router.

EsynetEvent::m_flit should provide the following information.

Fields	Data type	Note
EsynetEvent::m_flit.m_id	long	Credit value.

EsynetFoundation provides EsynetFoundation::receiveCreditMessage method to handle CREDIT event. The network platform calls the router or NI specified by EsynetEvent::m_des_id to respond CREDIT event. See also [flow control] for more information.

NI read event

NI read event (NIREAD) means a packet should be ejected from the network. Network interfaces and the integration APIs generate NIREAD events.

EsynetEvent provides EsynetEvent::generateNIReadEvent to generate a NIREAD event. NIREAD event should provide the following information.

Fields	Data type	Note
EsynetEvent::m_event_time	double	The ejection time of the packet.
EsynetEvent::m_event_type	long	EsynetEvent::NIREAD.
EsynetEvent::m_src_id	long	The NI id.

EsynetFoundation provides EsynetFoundation::receiveNireadMessage method to handle NIREAD event. The network platform calls the NI specified by EsynetEvent::m_des_id to respond NIREAD event. NI ejects one packet out from the eject queue. See also NI pipeline for more information.