1README for Garnet2.0
2Written By: Tushar Krishna (tushar@ece.gatech.edu)
3Last Updated: Jul 9, 2016
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5
6Garnet Network Parameters and Setup:
7- GarnetNetwork.py
8    * defaults can be overwritten from command line (see configs/network/Network.py)
9- GarnetNetwork.hh/cc
10    * sets up the routers and links
11    * collects stats
12
13
14CODE FLOW
15- NetworkInterface.cc::wakeup()
16    * Every NI connected to one coherence protocol controller on one end, and one router on the other.
17    * receives messages from coherence protocol buffer in appropriate vnet and converts them into network packets and sends them into the network.
18        * garnet2.0 adds the ability to capture a network trace at this point.
19    * receives flits from the network, extracts the protocol message and sends it to the coherence protocol buffer in appropriate vnet.
20    * manages flow-control (i.e., credits) with its attached router.
21    * The consuming flit/credit output link of the NI is put in the global event queue with a timestamp set to next cycle.
22      The eventqueue calls the wakeup function in the consumer.
23
24- NetworkLink.cc::wakeup()
25    * receives flits from NI/router and sends it to NI/router after m_latency cycles delay
26        * Default latency value for every link can be set from command line (see configs/network/Network.py)
27        * Per link latency can be overwritten in the topology file
28    * The consumer of the link (NI/router) is put in the global event queue with a timestamp set after m_latency cycles.
29      The eventqueue calls the wakeup function in the consumer.
30
31- Router.cc::wakeup()
32    * Loop through all InputUnits and call their wakeup()
33    * Loop through all OutputUnits and call their wakeup()
34    * Call SwitchAllocator's wakeup()
35    * Call CrossbarSwitch's wakeup()
36    * The router's wakeup function is called whenever any of its modules (InputUnit, OutputUnit, SwitchAllocator, CrossbarSwitch) have
37      a ready flit/credit to act upon this cycle.
38
39- InputUnit.cc::wakeup()
40    * Read input flit from upstream router if it is ready for this cycle
41    * For HEAD/HEAD_TAIL flits, perform route computation, and update route in the VC.
42    * Buffer the flit for (m_latency - 1) cycles and mark it valid for SwitchAllocation starting that cycle.
43        * Default latency for every router can be set from command line (see configs/network/Network.py)
44        * Per router latency (i.e., num pipeline stages) can be set in the topology file
45
46- OutputUnit.cc::wakeup()
47    * Read input credit from downstream router if it is ready for this cycle
48    * Increment the credit in the appropriate output VC state.
49    * Mark output VC as free if the credit carries is_free_signal as true
50
51- SwitchAllocator.cc::wakeup()
52    * Note: SwitchAllocator performs VC arbitration and selection within it.
53    * SA-I (or SA-i): Loop through all input VCs at every input port, and select one in a round robin manner.
54        * For HEAD/HEAD_TAIL flits only select an input VC whose output port has at least one free output VC.
55        * For BODY/TAIL flits, only select an input VC that has credits in its output VC.
56    * Place a request for the output port from this VC.
57    * SA-II (or SA-o): Loop through all output ports, and select one input VC (that placed a request during SA-I) as the winner for this output port in a round robin manner.
58        * For HEAD/HEAD_TAIL flits, perform outvc allocation (i.e., select a free VC from the output port).
59        * For BODY/TAIL flits, decrement a credit in the output vc.
60    * Read the flit out from the input VC, and send it to the CrossbarSwitch
61    * Send a increment_credit signal to the upstream router for this input VC.
62        * for HEAD_TAIL/TAIL flits, mark is_free_signal as true in the credit.
63        * The input unit sends the credit out on the credit link to the upstream router.
64    * Reschedule the Router to wakeup next cycle for any flits ready for SA next cycle.
65
66- CrossbarSwitch.cc::wakeup()
67    * Loop through all input ports, and send the winning flit out of its output port onto the output link.
68    * The consuming flit output link of the router is put in the global event queue with a timestamp set to next cycle.
69      The eventqueue calls the wakeup function in the consumer.
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