Changes between Initial Version and Version 1 of Writing Rules/TLM2

Timestamp:

Sep 18, 2008, 3:15:53 PM (17 years ago)

Author:

alain

Comment:

--

Writing Rules/TLM2

@@ +1 @@
+ {{{
+#!html
+<h1>Writing efficient TLM-T SystemC simulation models for SoCLib</h1>
+}}}
+
+Authors : Alain Greiner, François Pêcheux, Emmanuel Viaud, Nicolas Pouillon
+ 
+[[PageOutline]]
+
+= A) Introduction =
+
+'''This document is under development'''.
+
+This new document describes the modeling rules for writing TLM-T SystemC simulation models for SoCLib.
+This is the second release, as the modeling rules have been modified to respect the TLM2.0 standard.
+
+In TLM2.0, both the '''payload''' (defining the actual content of the exchanged packets), and the '''phase'''
+(defining the actual communication protocol steps) are template parameters.
+Therefore, specific '''payload''' and '''phase''' types have been defined for SoCLib.
+Those types are well suited for the VCI/OCP protocol, but they more general and can
+used to describe any shared-memory architecture using routed network on chip.
+  
+The TLM-T rules used in SoCLib enforce the PDES (Parallel Discrete Event Simulation) principles. Each PDES process involved in 
+the simulation has its own local time, and PDES processes synchronize through messages piggybacked with time information. 
+Models complying to these rules can be used with the "standard" OSCI simulation engine (SystemC 2.x), but can 
+also be used also with others simulation engines, especially distributed, parallelized simulation engines.
+
+Before writing a new model, it is useful to have a look at the [WritingRules/General general SoCLib rules].
+
+= B) Single VCI initiator and single VCI target =
+
+Figure 1 presents a minimal system containing one single initiator, '''!VciSimpleInitiator''' , and one single 
+target, '''!VciSimpleTarget''' . The '''!VciSimpleInitiator''' module behavior is modeled by 
+the SC_THREAD  '''execLoop()''', that contains an infinite loop.
+
+[[Image(tlmt_figure_1.png, nolink)]]
+
+Unlike the initiator, the target module has a purely reactive behaviour and there is no  need to use a SC_THREAD : 
+The target behaviour is entirely described by the call-back function,
+that is executed in the context of the '''execLoop() thread when a VCI command packet is received by the target module.
+
+The VCI communication channel is a point-to-point bi-directionnal channel, encapsulating two separated uni-directionnal 
+channels: one to transmit the VCI command packet, one to transmit the VCI response packet.
+
+= C) VCI initiator Modeling =
+
+In the proposed example, the initiator module is modeled by the '''!VciSimpleInitiator''' class. 
+This class inherits from the '''soclib::tlmt::!BaseModule''' class, that acts as the root class for all TLM-T modules. 
+The process time, as well as other useful process attributes, is contained in a C++ structure called 
+a '''tlmt_core::tlmt_thread_context'''. As there is only one thread in this module, there is only one member 
+variable '''c0''' of type '''tlmt_core::tlmt_thread_context'''. '''c0''' mostly contains the PDES process local 
+time ('''H''' on the figure). In all the TLM-T models, time is handled by the '''tlmt_core::tlmt_time''' class. 
+In order to get the time associated to the initiator process, one should use the getter 
+function '''time()''' on the '''c0''' object, and should use the setter functions
+'''set_time()''' and '''update_time()''' to assign a new time to the PDES process.
+
+The '''execLoop()''' method, describing the initiator behaviour must be declared as a member function of 
+the '''!VciSimpleInitiator''' class. 
+
+Finally, the class '''!VciSimpleInitiator''' must contain a member variable '''p_vci''', of type '''!VciInitiator'''. 
+This object has a template parameter <'''vci_param'''> defining the widths of the VCI ADDRESS and DATA fields.
+
+== C.1) Sending a VCI command packet ==
+
+To send a VCI command packet, the '''execLoop()''' method must use the '''send()''' method, that is a member function of 
+the '''p_vci''' port. The prototype is the following:
+{{{
+void send(soclib::tlmt::vci_cmd_packet<vci_param> *cmd, // pointer to a VCI command packet      
+          tlmt_core::tlmt_time time);                   // initiator local time
+}}}
+
+The contents of a VCI command packet is defined below:
+{{{
+template<typename vci_param>
+class vci_cmd_packet
+{
+public:
+        typename vci_param::cmd_t cmd;        // VCI transaction type
+        typename vci_param::addr_t address;   // address on the target side 
+        uint32_t int be;                      // byte_enable value (same value for all packet words)
+        bool contig;                          // contiguous addresses (when true)
+        typename vci_param::data_t *buf;      // pointer to the local buffer on the initiator
+        size_t nwords;                        // number of words in the packet
+        uint32_t srcid;                       // VCI Source ID
+        uint32_t trdid;                       // VCI Thread ID
+        uint32_t pktid;                       // VCI Packet ID
+};
+}}}
+
+The possible values for the '''cmd''' filed are  `vci_param::CMD_READ`, `vci_param::CMD_WRITE`, `vci_param::CMD_READ_LOCKED`,
+and `vci_param::CMD_STORE_COND`.
+The '''contig''' field can be used for optimization.
+
+The '''send()''' function is non-blocking. 
+To implement a blocking transaction (such as a cache line read, where the processor is ''frozen'' during the VCI transaction), 
+the model designer must use the SystemC '''sc_core::wait(x)''' primitive ('''x''' being of type '''sc_core::sc_event'''): 
+the '''execLoop()''' thread is then suspended, and will be reactivated when the response packet is actually received.
+
+== C.2) Receiving a VCI response packet ==
+
+To receive a VCI response packet, a call-back function must be defined as a member function of the 
+class '''!VciSimpleInitiator'''. This call-back function (named '''rspReceived()''' in the example), must be
+declared in the '''!VciSimpleInitiator''' class and
+is executed each time a VCI response packet is received on the '''p_vci''' port. The function name is not 
+constrained, but the arguments must respect the following prototype:
+{{{
+tlmt_core::tlmt_return &rspReceived(soclib::tlmt::vci_rsp_packet<vci_param> *pkt,
+         const tlmt_core::tlmt_time &time,
+         void *private_data);
+}}}
+
+The contents of a VCI response packet is defined below:
+{{{
+template<typename vci_param>
+class vci_rsp_packet
+{
+public:
+        typename vci_param::cmd_t cmd;    // VCI transaction type
+        size_t nwords;                    // number of words in the packet
+        uint32_t error;                   // error code (0 if no error)
+        uint32_t srcid;                   // VCI Source ID
+        uint32_t trdid;                   // VCI Thread ID
+        uint32_t pktid;                   // VCI Packet ID
+};
+}}}
+
+The second parameter, '''time''', is of type '''tlmt_core::tlmt_time''' and corresponds to the time of the response. The third parameter, 
+'''private_data''' has a default value of '''NULL''' and is not used when transmitting or receiving VCI packets.
+
+
+The actions executed by the call-back function depend on the response transaction type ('''cmd''' field), as well as 
+the '''pktid''' and '''trdid''' fields.
+
+In the proposed example :
+ * In case of of a blocking read , the call-back function updates the local time, and reactivates the suspended thread.
+ * In case of a non-blocking write, the call-back function does nothing.
+ 
+== C.3) Initiator Constructor ==
+
+The constructor of the class '''!VciSimpleInitiator''' must initialize all the member variables, including 
+the '''p_vci''' port. The '''rspReceived()''' call-back function being executed in the context of the thread sending 
+the response packet, a link between the '''p_vci''' port and the call-back function must be established. 
+Moreover, the '''p_vci''' port must contain a pointer to the initiator thread context '''c0'''. This allows the target to
+get information on the initiator that actually sends VCI packets (the initiator local time, the initiator activity, etc).
+
+The '''!VciInitiator''' constructor for the '''p_vci_''' object must be called with the following arguments:
+{{{
+p_vci("vci", new tlmt_core::tlmt_callback<VciSimpleInitiator,soclib::tlmt::vci_rsp_packet<vci_param> *>(
+                                         this, &VciSimpleInitiator<vci_param>::rspReceived), &c0)
+}}}
+  
+== C.4) Lookahead parameter ==
+
+The SystemC simulation engine behaves as a cooperative, non-preemptive multi-tasks system. Any thread in the system must stop execution 
+after at some point, in order to allow the other threads to execute. With the proposed approach, a TLM-T initiator will never stop if 
+it does not execute blocking communication (such as a processor that has all code and data in the L1 caches). 
+
+To solve this issue, it is necessary to define -for each initiator module- a '''lookahead''' parameter. This parameter defines the maximum 
+number of cycles that can be executed by the thread before it is automatically stopped. The '''lookahead''' parameter allows the system designer 
+to bound the de-synchronization time interval between threads. 
+
+A small value for this parameter results in a better timing accuracy for the simulation, but implies a larger number of context switches, 
+and a slower simulation speed. 
+
+== C.4) VCI initiator example ==
+
+{{{
+
+////////////////////////// vci_simple_initiator.h ////////////////////////////////
+
+#ifndef VCI_SIMPLE_INITIATOR_H
+#define VCI_SIMPLE_INITIATOR_H
+
+#include <tlmt>
+#include "tlmt_base_module.h"
+#include "vci_ports.h"
+
+namespace soclib { namespace tlmt {
+
+template<typename vci_param>
+class VciSimpleInitiator
+    : public soclib::tlmt::BaseModule
+{
+    tlmt_core::tlmt_thread_context c0;
+    sc_core::sc_event m_rsp_received;
+    tlmt_core::tlmt_return m_return;
+    soclib::tlmt::vci_cmd_packet<vci_param> cmd;
+
+    uint32_t addresses[8];       // address table,
+    uint32_t localbuf[8];        // local buffer
+    
+    uint32_t m_counter;          // iteration counter
+    uint32_t m_lookahead;        // lookahead value
+    uint32_t m_index;            // initiator index
+    
+protected:
+    SC_HAS_PROCESS(VciSimpleInitiator);
+
+public:
+    soclib::tlmt::VciInitiator<vci_param> p_vci;
+
+    VciSimpleInitiator( sc_core::sc_module_name name,
+                                uint32_t initiator index,
+                                uint32_t lookahead );
+
+    tlmt_core::tlmt_return &rspReceived(soclib::tlmt::vci_rsp_packet<vci_param> *pkt,
+         const tlmt_core::tlmt_time &time,
+         void *private_data);
+    void behavior();
+};
+
+}}
+
+#endif
+
+////////////////////////// vci_simple_initiator.cpp ////////////////////////////////
+
+#include "../include/vci_simple_initiator.h"
+
+namespace soclib { namespace tlmt {
+
+#define tmpl(x) template<typename vci_param> x VciSimpleInitiator<vci_param>
+
+tmpl(tlmt_core::tlmt_return&)::rspReceived(soclib::tlmt::vci_rsp_packet<vci_param> *pkt,
+        const tlmt_core::tlmt_time &time,
+        void *private_data)
+{
+    if(pkt->cmd == vci_param::VCI_CMD_READ) { 
+        c0.set_time(time + tlmt_core::tlmt_time(pkt->length));
+        m_rsp_received.notify(sc_core::SC_ZERO_TIME) ;
+    }
+    return m_return;
+}
+
+tmpl(void)::behavior()
+{
+
+        for(;;) {
+
+                // sending a read VCI packet
+                
+                cmd.cmd = vci_param::CMD_READ;  // a VCI read packet
+                addresses[0] = 0xBFC00000;      // the start address
+                cmd.address = addresses;        // assigned 
+                cmd.be = 0xF;                   // reading full words
+                cmd.contig = true;              // at successive addresses
+                cmd.buf = localbuf;             // storing the read results in localbuf
+                cmd.length = 8;                 // packet of 8 words
+                cmd.srcid = 0;                  // srcid=0
+                cmd.trdid = 0;                  // trdid=0
+                cmd.pktid = 0;                  // pktid=0
+
+                tlmt_core::tlmt_return ret;        // in case a test on the send function is needed
+                ret = p_vci.send(&cmd, c0.time()); // sending the packet 
+                sc_core::wait(m_rsp_received);     // and waiting for the response packet
+
+                // sending a write VCI packet
+                
+                localbuf[0]=0x00112233;         // first, fill the write local buffer with write data
+                
+                cmd.cmd = vci_param::CMD_WRITE; // then issue the VCI write packet
+                addresses[0] = 0x10000000;      // starting with this address
+                cmd.address = addresses;
+                cmd.be = 0xF;
+                cmd.contig = 0;
+                cmd.buf = localbuf;
+                cmd.length = 1;
+                cmd.srcid = 0;
+                cmd.trdid = 0;
+                cmd.pktid = 0;
+
+                ret = p_vci.send(&cmd, c0.time()); // Don't wait for the answer
+
+                // lookahead management
+                m_counter++ ;
+                if (m_counter >= m_lookahead) {
+                   m_counter = 0 ;
+                   sc_core::wait(sc_core::SC_ZERO_TIME) ;
+                } // end if
+                
+                // process time= process time+1
+                c0.set_time(c0.time()+tlmt_core::tlmt_time(1)) ;
+
+        }
+}
+
+tmpl(/**/)::VciSimpleInitiator( sc_core::sc_module_name name,
+                                uint32_t initiator index,
+                                uint32_t lookahead)
+                   : soclib::tlmt::BaseModule(name),
+                     m_index(initiator_index),
+                     m_lookahead(lookahead),
+                     m_counter(0),
+                   p_vci("vci", new tlmt_core::tlmt_callback<VciSimpleInitiator,soclib::tlmt::vci_rsp_packet<vci_param> *>(
+                                         this, &VciSimpleInitiator<vci_param>::rspReceived), &c0)
+{
+        SC_THREAD(behavior);
+}
+
+}}
+
+}}}
+
+= D) VCI target modeling =
+
+In the proposed example, the target handles two types of command: a read burst of 8 words, and a write burst of 8 words. 
+To simplify the model, there is no error management.
+
+The class '''!VciSimpleTarget''' inherits from the class '''!BaseModule'''. The class '''!VciSimpleTarget''' contains a member 
+variable '''p_vci''' of type '''!VciTarget'''. This object has a template parameter '''<vci_param>''' defining the widths of 
+the VCI ADDRESS and DATA fields.
+
+== D.1) Receiving a VCI command packet ==
+
+To receive a VCI command packet, a call-back function must be defined as a member function of the class '''!VciSimpleTarget'''. 
+This call-back function (named '''cmdReceived()''' in the example), will be executed each time a VCI command packet is received on 
+the '''p_vci''' port. The function name is not constrained, but the arguments must respect the following prototype:
+{{{
+tlmt_core::tlmt_return &cmdReceived(soclib::tlmt::vci_cmd_packet<vci_param> *pkt,
+         const tlmt_core::tlmt_time &time,
+         void *private_data);
+}}}  
+For the read and write transactions, the actual data transfer is performed by this '''cmdReceived()''' function.
+To avoid multiple data copies, only the pointer on the initiator data buffer is transported in the VCI command packet 
+(source buffer for a write transaction, or destination buffer for a read transaction).
+
+== D.2) Sending a VCI response packet ==
+
+To send a VCI response packet the '''cmdReceived()''' function must use the '''send()''' method, that is a member function of 
+the class '''!VciTarget''', and has the following prototype:
+{{{
+void send(soclib::tlmt::vci_rsp_packet<vci_param> *rsp, // pointer to a VCI response packet     
+          tlmt_core::tlmt_time time);                   // initiator local time 
+}}}
+For a reactive target, the response packet time is computed as the command packet time plus the target intrinsic latency.
+
+== D.3) Target Constructor ==
+
+The constructor of the class '''!VciSimpleTarget''' must initialize all the member variables, including 
+the '''p_vci''' port. The '''cmdReceived()''' call-back function being executed in the context of the thread sending the command packet, 
+a link between the '''p_vci''' port and the call-back function must be established. 
+The '''!VciTarget''' constructor must be called with the following arguments:
+{{{
+p_vci("vci", new tlmt_core::tlmt_callback<VciSimpleTarget,soclib::tlmt::vci_cmd_packet<vci_param> *>(
+                                   this, &VciSimpleTarget<vci_param>::cmdReceived))
+}}}
+  
+== D.4) VCI target example ==
+ {{{
+
+////////////////////////// vci_simple_target.h ////////////////////////////////
+
+#ifndef VCI_SIMPLE_TARGET_H
+#define VCI_SIMPLE_TARGET_H
+
+#include <tlmt>
+#include "tlmt_base_module.h"
+#include "vci_ports.h"
+
+namespace soclib { namespace tlmt {
+
+template<typename vci_param>
+class VciSimpleTarget 
+    : public soclib::tlmt::BaseModule
+{
+private:
+    tlmt_core::tlmt_return m_return;
+    uint32_t m_index;
+    uint32_t m_latency;
+    soclib::tlmt::vci_rsp_packet<vci_param> rsp;
+    
+public:
+    soclib::tlmt::VciTarget<vci_param> p_vci;
+
+    VciSimpleTarget(sc_core::sc_module_name name,
+              uint32_t  targetIndex,
+              uint32_t  latency);
+
+    tlmt_core::tlmt_return &cmdReceived(soclib::tlmt::vci_cmd_packet<vci_param> *pkt,
+         const tlmt_core::tlmt_time &time,
+         void *private_data);
+};
+
+}}
+
+#endif
+
+////////////////////////// vci_simple_target.cpp ////////////////////////////////
+
+#include "../include/vci_simple_target.h"
+
+namespace soclib { namespace tlmt {
+
+#define tmpl(x) template<typename vci_param> x VciSimpleTarget<vci_param>
+
+tmpl(tlmt_core::tlmt_return&)::cmdReceived(soclib::tlmt::vci_cmd_packet<vci_param> *pkt,
+        const tlmt_core::tlmt_time &time,
+        void *private_data)
+{
+    uint32_t m_data[128];
+        
+    if(pkt->cmd == vci_param::VCI_CMD_WRITE) { 
+        for(int i = 0 ; i < pkt->length ; i++) 
+                m_data[i] = cmd->buf[i];
+        }
+    if(pkt->cmd == vci_param::VCI_CMD_READ) {
+        for(int i = 0 ; i < pkt->length ; i++) 
+                cmd->buf[i] = m_data[i];
+        }
+    rsp.srcid = pkt->srcid;
+    rsp.trdid  = pkt->trdid;
+    rsp.pktid = pkt->pktid;
+    rsp.length = pkt->length;
+    rsp.error = 0;
+    p_vci.send(&m_rsp, time+tlmt_core::tlmt_time(latency+pkt->length)) ;
+    m_return.time=time+tlmt_core::tlmt_time(latency+pkt->length;
+    return (m_return);
+}
+
+tmpl(/**/)::VciSimpleTarget(sc_core::sc_module_name name,
+              uint32_t  targetIndex,
+              uint32_t  latency)
+        : soclib::tlmt::BaseModule(name),
+        m_index(targetIndex),
+        m_latency(latency),
+        p_vci("vci", new tlmt_core::tlmt_callback<VciSimpleTarget,soclib::tlmt::vci_cmd_packet<vci_param> *>(
+                                   this, &VciSimpleTarget<vci_param>::cmdReceived))
+{
+}
+
+}}
+
+}}}
+
+= E) VCI Interconnect =
+
+The VCI interconnect used for the TLM-T simulation is a generic simulation model, named '''!VciVgmn'''.
+The two main parameters are the number of initiators, and the number of targets. In TLM-T simulation,
+we don't want to reproduce the cycle-accurate behavior of a particular interconnect. We only want to simulate the contention in 
+the network, when several VCI intitiators try to reach the same VCI target.
+Therefore, the network is actually modeled as a complete cross-bar : In a physical network such as the multi-stage network described 
+in Figure 2.a, conflicts can appear at any intermediate switch. In the '''!VciVgmn''' network described in Figure 2.b, conflicts can 
+only happen at the output ports. It is possible to specify a specific latency for each input/output couple. As in most physical 
+interconnects, the general arbitration policy is round-robin.
+
+[[Image(tlmt_figure_2.png, nolink)]]
+
+== E.1) Generic network modeling ==
+
+ There is actually two fully independent networks for VCI command packets and VCI response packets. There is a routing function for each input 
+ port, and an arbitration function for each output port, but the two networks are not symmetrical :
+ * For the command network, the arbitration policy is distributed: there is one arbitration thread for each output port 
+ (i.e. one arbitration thread for each VCI target). Each arbitration thread is modeled by a SC_THREAD, and contains a local clock.
+ * For the response network, there are no conflicts, and there is no need for arbitration. Therefore, there is no thread 
+ (and no local time) and the response network is implemented by simple function calls.
+
+This is illustrated in Figure 3 for a network with 2 initiators and three targets :  
+
+[[Image(tlmt_figure_3.png, nolink)]]
+
+== E.2) VCI initiators and targets synchronizations ==
+
+As described in sections B & C, each VCI initiator TLM-T module contains a thread and a local clock. But, in order to increase the TLM-T simulation 
+speed,  the VCI targets are generally described as reactive call-back functions. Therefore, there is no thread, and no local clock in the TLM-T 
+module describing a VCI target. For a VCI target, the local clock is actually the clock associated to the corresponding arbitration 
+thread contained in the '''!VciVgmn''' module.
+
+As described in Figure 4, when a VCI command packet - sent by the corresponding arbitration thread - is received by a VCI target, 
+two synchronization mechanisms are activated :
+ * The '''cmdReceived()''' function sends a VCI response packet with an associated time to the source initiator, through 
+ the '''!VciVgmn''' response network. The corresponding time can be used to update the initiator local clock.
+ * The '''cmdReceived()''' function returns a time to the arbitration thread. This time is used to update the arbitration thread local 
+ clock.  
+
+[[Image(tlmt_figure_4.png, nolink)]]
+
+= F) Interrupt modeling =
+
+Interrupts are asynchronous events that are not carried by the VCI network.
+
+As illustrated in Figure 5, each interrupt line is modeled by a specific point to point, uni-directional channel. This channel uses two ports of 
+type '''tlmt_core::tlmt_out<bool>''' and '''tlmt_core::tlmt_in<bool>''' that must be declared as member variables of the source and 
+destination modules respectively.
+
+[[Image(tlmt_figure_5.png, nolink)]]
+
+== F.1) Source modeling ==
+
+The source module (named '''!VciSimpleSourceInterrupt''' in this example) must contain a member variable '''p_irq''' of 
+type '''tlmt_core::tlmt_out<bool>'''. To activate, or desactivate an interruption, the source module must use the '''send()''' method, 
+that is a member function of the '''tlmt_core::tlmt_out<bool>''' class. These interrupt packets transport both a Boolean, 
+and a time. The '''send()''' prototype is defined as follows :
+{{{
+void  send( bool  val, const tlmt_core::tlmt_time &time)
+}}}
+
+== F.2) Destination modeling ==
+
+The destination module (named here '''!VciProcessor''') must contain a member variable '''p_irq''' of type
+'''tlmt_core::tlmt_in<bool>''', and a call-back function (named here '''irqReceived()''' that is executed when an interrupt 
+packet is received on the '''p_irq''' port.
+
+A link between the '''p_irq''' port and the call-back function must be established by the port constructor in the constructor of 
+the class '''VciProcessor''' :
+{{{
+tlmt_core::tlmt_callback < VciProcessor,bool >(this, &VciProcessor < iss_t,
+           vci_param >::irqReceived);
+}}}
+
+In the Parallel Discrete Event Simulation, the pessimistic approach relies on the fact that any PDES process is not allowed to update 
+his local time until it has received messages on all its input ports with times greater than its local time.
+
+Therefore, a SC_THREAD modeling the behavior of a processor containing an '''tlmt_core::tlmt_in<bool>''' should in principle 
+wait a timestamped packet on its interrupt port before executing instructions. However, such a behavior would be very inefficient, 
+and is prone to dead-lock situations.
+
+The recommended policy for handling interrupts is the following:
+ * The call-back function '''irqReceived()''' sets the member variables '''m_irqpending''' and '''m_irqtime''', when a interrupt packet 
+ is received on the '''p_irq''' port.
+ * The '''execLoop()''' thread must test the '''m_irqpending''' variable at each cycle (i.e. in each iteration of 
+ the infinite loop).
+ * If there is no interrupt pending, the thread continues its execution. If an interrupt is pending, and the interrupt time is greater 
+ than the local time, the thread continues execution. If the interrupt time is equal or smaller than the local time, the interrupt 
+ is handled.
+
+Such a violation of the the pessimistic parallel simulation principles creates a loss of accuracy on the interrupt handling 
+timestamp. This loss of accuracy in the TLM-T simulation is acceptable, as interrupts are asynchronous events, and the timing error 
+is bounded by the '''m_lookahead''' parameter.
+
+== F.3)  Processor with interrupt example ==
+
+{{{
+
+////////////////////////// vci_processor.h ////////////////////////////////
+
+namespace soclib { namespace tlmt {
+
+template<typename iss_t,typename vci_param>
+class VciProcessor
+    : public soclib::tlmt::BaseModule
+{
+    tlmt_core::tlmt_thread_context c0;
+    sc_core::sc_event m_rsp_received;
+    tlmt_core::tlmt_return m_return;
+    bool  m_irqpendig;  // pending interrupt request
+    tlmt_core::tlmt_time  m_irqtime;  // irq date
+    uint32_t  m_counter;  // iteration counter
+    uint32_t  m_lookahead;  // lookahead value
+    
+protected:
+    SC_HAS_PROCESS(VciProcessor);
+
+public:
+    soclib::tlmt::VciInitiator<vci_param> p_vci;
+    tlmt_core::tlmt_in<bool> p_irq;
+
+    VciProcessor( sc_core::sc_module_name name, int id );
+
+    tlmt_core::tlmt_return &rspReceived(soclib::tlmt::vci_rsp_packet<vci_param> *pkt,
+                const tlmt_core::tlmt_time &time,
+                void *private_data);
+    tlmt_core::tlmt_return &irqReceived(bool,
+                const tlmt_core::tlmt_time &time,
+                void *private_data);
+    void execLoop();
+};
+
+}}
+
+////////////////////////// vci_processor.cpp ////////////////////////////////
+
+#include "../include/vci_processor.h"
+
+namespace soclib
+{
+  namespace tlmt
+  {
+
+#define tmpl(x) template<typename iss_t, typename vci_param> x VciProcessor<vci_param>
+
+    tmpl (tlmt_core::tlmt_return &)::rspReceived (soclib::tlmt:: vci_rsp_packet < vci_param > *pkt,
+                                                  const tlmt_core:: tlmt_time & time, void *private_data)
+    {
+      if (pkt->cmd == vci_param::CMD_WRITE)
+        m_write_error = (pkt->error != 0);
+      else
+        m_write_error = false;
+      if (pkt->cmd == vci_param::CMD_READ)
+        m_read_error = (pkt->error != 0);
+      else
+        m_read_error = false;
+      m_rsptime = time + tlmt_core::tlmt_time (pkt->length);
+      m_vci_pending = false;
+      m_rsp_received.notify (sc_core::SC_ZERO_TIME);
+
+      return m_return;
+    }
+
+    tmpl (tlmt_core::tlmt_return &)::irqReceived (bool v, const tlmt_core::
+                                                  tlmt_time & time, void *private_data)
+    {
+      m_irqpending = val;
+      m_irqtime = time;   
+    
+      return m_return;
+    }
+
+
+    tmpl (void)::execLoop ()
+        { 
+                while(1) {
+                        ...
+                        // test interrupts
+                        if (m_irqpending && (m_irqtime <= c0.time())) 
+                        {
+                                // interrupt handling   
+                        }
+                                ...
+                        // lookahead management
+                        m_counter++ ;
+                        if (m_counter >= m_lookahead) {
+                                m_counter = 0 ;
+                                sc_core::wait(sc_core::SC_ZERO_TIME) ;
+                        } // end if
+                        c0.set_time(c0.time()+tlmt_core::tlmt_time(1)) ;
+                } // end while
+        }
+        
+  tmpl ( /**/)::VciProcessor(
+          sc_core::sc_module_name name,
+          int id )
+: soclib::tlmt::BaseModule (name),
+  m_counter (0), 
+  m_lookahead (10),
+  p_vci("vci",new tlmt_core::tlmt_callback<VciProcessor,vci_rsp_packet<vci_param>*>(
+        this,&VciProcessor<vci_param>::rspReceived),&c0),
+  p_irq("irq",new tlmt_core::tlmt_callback<VciProcesspr,bool>(
+        this,&VciProcessor<vci_param>::irqReceived))
+    {
+      SC_THREAD (execLoop);
+    }
+
+}}
+
+}}}
+