Classifications

• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
  • G06F13/14—Handling requests for interconnection or transfer
  • G06F13/20—Handling requests for interconnection or transfer for access to input/output bus
  • G06F13/28—Handling requests for interconnection or transfer for access to input/output bus using burst mode transfer, e.g. direct memory access DMA, cycle steal
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
  • G06F13/14—Handling requests for interconnection or transfer
  • G06F13/36—Handling requests for interconnection or transfer for access to common bus or bus system
  • G06F13/362—Handling requests for interconnection or transfer for access to common bus or bus system with centralised access control
  • G06F13/364—Handling requests for interconnection or transfer for access to common bus or bus system with centralised access control using independent requests or grants, e.g. using separated request and grant lines
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
  • G06F13/38—Information transfer, e.g. on bus
  • G06F13/40—Bus structure
  • G06F13/4004—Coupling between buses
  • G06F13/4022—Coupling between buses using switching circuits, e.g. switching matrix, connection or expansion network
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F13/00—Interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
  • G06F13/38—Information transfer, e.g. on bus
  • G06F13/42—Bus transfer protocol, e.g. handshake; Synchronisation
  • G06F13/4282—Bus transfer protocol, e.g. handshake; Synchronisation on a serial bus, e.g. I2C bus, SPI bus
• • G—PHYSICS
  • G06—COMPUTING OR CALCULATING; COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F2213/00—Indexing scheme relating to interconnection of, or transfer of information or other signals between, memories, input/output devices or central processing units
  • G06F2213/0038—System on Chip

Definitions

• the invention relates to the field of systems-on-chip often referred to as the English word System on chip or its abbreviation SoC.
• the invention relates more particularly to systems on a chip in which interconnections between modules are performed by internal computer buses.
• SoC system-on-a-chip
• SoC is a complete on-chip system that can include one or more processors, memory, interface devices, and / or other components required to perform a complex function.
• SoCs generally have a hierarchical architecture: "master” modules perform requests for read or write access to so-called “slave” modules.
• masters are processors or DMA controllers
• slaves are storage memories or network devices.
• Interconnections between masters and slaves are typically supported by internal computer buses compatible with one or more communication protocols.
• AMBA Advanced Microcontroller Bus Architecture
• AHB Advanced High-Performance Bus
• AXI Advanced Extensible Interface
• a computer bus B provides interconnections between k master modules Mi, iel, kj and n modules. Sj slaves, I ll, n ⁇ .
• the bus B comprises k slave ports PSi, ie l. k on each of which is connected a master module, and n master ports PMj, I [l, n], on each of which is connected a slave module.
• the bus is seen as a slave by each master module, and seen as a master by each slave module.
• data can be transmitted according to a specific communication protocol.
• the bus B comprises internal routing means, for example one or more switch stages represented in FIG. 1 by dashed arrows. These means ensure the routing of communications between a master and a slave.
• the bus B illustrated in FIG. 1 carries out all possible interconnections between one of the k masters and one of the n slaves, ie k * n interconnections.
• the slave S1 can for example receive requests issued by the several masters, and be shared access alternately between them.
• the master M1 may be in the process of accessing S1 while the master M2 remains on hold. Once the access by M1 is completed, the master M2 can in turn make an access to S1.
• the invention aims to solve the problems of the prior art.
• the invention particularly relates to a bandwidth control method in a system-on-a-chip system comprising at least one main master module, at least one secondary master module, at least one slave module and a bus connected to each module on a single module. communication link, the bus comprising interconnection means for communicating at least one common slave module with at least one main master module and with at least one secondary master module with at least one common road portion, the method comprising the steps following performed for each common slave module:
• the described method notably makes it possible to reserve bandwidth for any main master module wishing to access a common slave module, both of which are interconnected by means of any commercially available AMBA computer bus.
• the adaptation of an AMBA computer bus for the needs of a system-on-a-chip with a high level of criticality is therefore not necessary.
• FIG. 1 schematically represents a known on-chip system.
• FIG. 3 represents a sequence of signals of the AXI protocol transmitted during a reading.
• FIG. 4 represents a signal sequence of the AXI protocol transmitted during a write.
• FIGS. 5a to 5d show step diagrams of the bandwidth control method according to the invention.
• FIG. 6 shows the evolution over time of the value of a counter associated with a common slave module as a function of detected requests.
• FIG. 7 schematically shows a system-on-chip protected by the bandwidth control device according to the invention.
• a transaction TRANSO, TRANSI between a master and a slave comprises at least two phases.
• the master module notably requests access to a slave that it accepts or refuses. If access is accepted, a second transfer phase DATAO, DATAI starts in which data is transferred by bursts from the master to the slave in the case of a write, or from the slave to the master in the case of 'a lecture.
• DATAO, DATAI starts in which data is transferred by bursts from the master to the slave in the case of a write, or from the slave to the master in the case of 'a lecture.
• information is exchanged between the master and the slave on parallel signals.
• the signals To perform a read or write transaction, the signals must be positioned in an ordered sequence comprising the request and transfer phases.
• the AXI protocol defines a single interface to describe transactions between a master module and a slave module, a master module and the slave port of a bus, or the master port of a bus and a slave module.
• This interface consists of five channels:
• Three dedicated writing channels (a control channel, a data channel and a response channel).
• the channels each carry a set of signals emitted by a source in a unidirectional manner.
• the read control channel carries request signals from a master to a slave, while the read data channel then returns data carrying signals from a slave to a master.
• FIG. 2 illustrates, for example, a signal positioning sequence for a reading according to the AXI protocol, carried out in four data transfers.
• the functions of the signals used are summarized in the table below:
• a read transaction according to the AXI protocol comprises the following steps.
• the ACLK signal is synchronized to a source clock.
• a master sends the signal ARADDR containing a read address A of the slave to which it wishes to access reading.
• the master sets the signal ARVALID to signify to the recipient slave the validity of the address A.
• the slave confirms the availability of address A by positioning the ARREADY signal.
• the master then sets the RREADY signal to one to indicate to the slave that he is ready to read data.
• FIG. 2 illustrates a burst of four transfers D (A0), D (A1), D (A2) and D (A3).
• the RVALID signal is set to one by the slave to signify to the master the validity of the data.
• the signal RLAST is set to one at the beginning of the last transfer D (A3).
• the reading illustrated in FIG. 2 is carried out in thirteen clock shots (between clock ticks TO and T13), eight of which are for the single data transfer phase.
• FIG. 3 shows an example of a signal positioning sequence for writing according to the AXI protocol also carried out in four data transfers.
• the functions of these signals are summarized in the table below:
• AWREADY Slave Indicates whether the slave is ready (1) or not (0) to accept a write address and associated control signals.
• WREADY Slave Indicates whether the slave is ready (1) or not (0) to receive write data.
• WVALID Master Indicates whether the write data is ready for transfer (1) or not (0) to the slave.
• WLAST Master Indicates the last write data transfer. BREADY Set to 1 to indicate that the master is ready to receive a write result, otherwise 0.
• a read transaction according to the AXI protocol comprises the following steps.
• the ACLK signal is synchronized to a source clock.
• a master transmits the AWADDR signal containing a write address A of the slave to which it wishes to access.
• the master sets the signal AWVALID to indicate to the receiving slave the validity of the address A.
• the slave confirms the availability of the address A by setting the signal AWREADY to one.
• the master then sets the WREADY signal to one to indicate to the slave that he is ready to transmit data to be written.
• FIG. 3 illustrates a burst of four transfers D (A0), D (A1), D (A2) and D (A3).
• the signal BREADY is set to one by the master to indicate that it is ready to receive a write result which will be transmitted at the end of the sequence.
• the signal WVALID is set to one by the master to signify to the slave the validity of the data to be written.
• the signal WLAST is set to one at the beginning of the last transfer.
• the slave then sets the BRESP signal to OKAY. This positioning is accompanied by a positioning of the signal BVALID to one during the duration of transmission of the OKAY value. The master finally repositions the BREADY signal to zero once this value is received.
• the writing illustrated in FIG. 3 is done in ten clock ticks (between clock ticks TO and T10), of which seven are for the data transfer phase alone.
• Other signals of the AXI protocol are in practice positioned during a reading or a writing but they are not detailed in this document for the sake of simplicity.
• the other protocols of the AMBA family (AHB, AHB-Lite, APB) follow the same general principle of write / write transaction realize the successive phases of request and data transfer with different signals.
• Each interface between an AMBA-compliant bus and a slave or master module can implement one of the AMBA family protocols.
• a system-on-a-chip comprising at least one main master module Ma, at least one secondary master module M1, Mi, Mk, at least one slave module S1, Sj, Sn and a bus B connected to each module by a communication link.
• the bus B comprises interconnection means for communicating at least one common slave module Sj with at least one main master module Ma and at least one secondary master module M1, Mi, Mk.
• a slave module says common "designates a slave module on which several competing master modules can access via bus B.
• the communication path between a secondary master module Mi and a slave module Sj comprises at least two communication links: a first communication link between the secondary master module Mi and a slave port PSi of the bus B, and a second communication link between a master port PMj of the bus B and the slave module Sj.
• the signals emitted by the secondary master module Mi pass through the slave port PSi, then are routed by the bus B to the master port PMj and are then transmitted to the slave module Sj connected to this master port PMj.
• the signals emitted by the slave module Sj destined for the secondary master Mi follow the same route in the opposite direction.
• the communication path between a main master module Ma and the slave module Sj comprises two communication links: a first communication link between the master module Ma and a slave port PSa of the bus B, and a second communication link between the master port PMj of the bus B and the common slave module Sj.
• the signals emitted by the master module Ma pass through the slave port PSa, then are routed by the bus B to the master port PMj and are then transmitted to the slave module Sj connected to this master port PMj.
• the signals emitted by the slave module Sj destined for the secondary master Mi follow the same route in the opposite direction.
• the two communication routes between the common slave module Sj and the competing master modules Ma and Mi therefore have at least a common portion of the road.
• This common road portion comprises at least the master port PMj and the communication link between this master port PMj and the common slave module Sj.
• a first access request to a common slave module Sj sent by a main master module Ma is detected.
• a blocking delay D j associated with the common slave module Sj is then determined in a step referenced "CALC".
• any transfer of data on the at least one common road portion between any secondary master module Mi and the common slave module Sj is blocked "BLOCK", and during the blocking delay D t determined previously.
• the shared common road portion with the main master module Ma is not occupied by data transferred between a secondary master module Mi and the common slave module Sj.
• bandwidth is released on the road communication between a main master module (for example the module Ma) and the common slave module Sj.
• the process can be repeated for all common system-on-a-chip slave modules.
• the blocking delay D j associated with a common slave module Sj can be varied according to the number of access requests to this module Sj transmitted by a set of master modules.
• the determination step CALC can comprise a reading of the value v j of the occurrence counter associated with the common slave module Sj and calculating the delay D j of blocking according to a predetermined formula.
• the blocking delay D j may for example be proportional to the value v j of the corresponding occurrence counter. We can also apply the following formula:
• T max is the duration of a predetermined data transfer between, for example the duration of a transfer of maximum size allowed in the system between a master module and a slave module.
• - T B is the duration of propagation of a request in the bus B.
• the occurrence counter Cj can moreover be decremented "DECR" after a second detection DET2 of a second request sent by a main master module that can access the common slave module Sj via the bus B, to another slave module Sj module.
• the main transmitting master module of the second request may be the transmitter of the first request, or more generally any master master module having a communication route linking it to the common slave module Sj.
• a secondary master wishing to access a common slave module will not be penalized if no master master module needs to access the same module Sj.
• the decrementation step DECR can be replaced by a complete reset of the occurrence counter Cj.
• the blocking step (BLOCK) may further comprise the following substeps repeated during the blocking delay D j :
• the secondary master module can, at the receiving the response signal, requesting another access to another module without wasting time transferring data that would be blocked anyway before reaching the common slave module Sj.
• the blocking step BLOCK can be performed unconditionally, or only if a condition is fulfilled.
• a condition may consist in comparing in a step referenced "TEST1" the value v j of the occurrence counter associated with the module Sj with a first occurrence threshold N j predetermined.
• This condition makes it possible to reserve a range of values for the occurrence counter Cj in which accesses to the common slave module are not considered to be disadvantageous because they do not consume enough bandwidth to delay requested accesses to the common slave module Sj in such a way that significant.
• a secondary master module wishing to access the common slave module Sj will not be penalized.
• this first threshold makes it possible not to systematically introduce blockages into the system, but only when the value of the counter leaves this range of values.
• the method may further include an additional step of "STAT" sending a status message to an interrupt controller (not shown in the figures) after BLOCK blocking.
• This STAT step in particular makes it possible to notify the current consumption of bandwidth to a master module, slave or any other third-party module of the system-on-a-chip.
• the STAT sending step can be performed unconditionally, or only if a condition is fulfilled.
• a condition may consist in comparing in a step referenced "TEST2" the value v j of the occurrence counter Cj associated with the module Sj with a second occurrence threshold N ' j predetermined.
• the second threshold N ' j may be greater than the first threshold N j . Only messages indicating bandwidth consumptions critical to the system are then notified in the STAT step.
• the method may also include steps of:
• This variant makes it possible to take into consideration the access frequency of all the main master modules to the common slave module Sj to calculate a blocking delay, and to sanction a secondary master module requiring access to this same common slave Sj.
• the time counter is initialized and started in a step "RESETT".
• the value of the timer is monitored. Each time (“TIMEOUT”) the value of this time counter crosses the time threshold 7), the occurrence counter Cj is decremented, and the time counter is reset and restarted RESETT.
• Each counter Cj may be an occurrence counter configured with an increment value equal to 1.
• each counter is a counter whose increment value is greater than 1.
• Each increment and decrement modifies the value of the counter by a value greater than 1.
• the value of the counter Cj is initially set to the value 1, and its increment to 1 also.
• step RESETT Occurs a first detection DET1 of a first access request sent by a main master module to the slave module Sj; the counter Cj is then incremented INCR to the value 2.
• the time counter associated with the slave module Sj is also initialized and started (step RESETT).
• time threshold 7 When the time threshold 7) is reached (TIMEOUT) by the time counter, a decrementation DECR of the occurrence counter Cj is carried out, its value becoming equal to 0.
• the time counter associated with the slave module Sj is also reset and restarted (RESETT).
• a third DET3 detection of a third access request sent by a main master module to the slave module Sj occurs before the time threshold 7) is reached again by the time counter associated with the module Sj.
• the counter Cj is then incremented to the value 1.
• the time counter associated with the slave module Sj is also reset and restarted (RESETT).
• the resetting / restarting step RESETT of the time counter associated with the common slave module Sj is performed for each first detection DET1, and / or each third detection DET3.
• the RESETT step can also be performed for each second detection DET2. Moreover, the detection steps DET1, DET2, DET3 can be performed on the communication link between the secondary master module Mi and the bus B. This detection slot makes it possible to distinguish simply and with certainty that the master module transmitting a request is secondary and not principal, and thus block access to a slave module in favor of a third master master module.
• the BLOCK blocking step can be performed on this same communication link. This ensures that only the secondary master module transmitting the access request to the common slave module Sj will be blocked.
• the detection steps DET1, DET2, DET3 may furthermore comprise substeps of
• the detecting steps DET1, DET2, DET3 and / or blocking BLOCK can moreover each be performed on a communication link according to a protocol according to the AMBA standard, such as the AXI protocol or the AHB protocol.
• AWADDR the AWVALID signal must be set to 1 to indicate the validity of the address
• ARADDR the ARVALID signal must be set to 1 to indicate the validity of the 'address
• AWREADY for write access
• ARREADY for read access
• a signal comprising an access address intercepted in the detection step HADDR (the signal HSELx must be set to 1 to signify the validity of the address),
• the time counter can moreover be synchronized with a clock used to synchronize communication signals between the master module and the slave module.
• the time counter can then increment for each rising edge detected on the ACLK signal of a communication link according to the AXI protocol; thus, the time threshold is seen as a maximum number of clock ticks.
• the bandwidth control method may be generalized to any protocol of the AMBA standard or to any combination of protocols of the AMBA family used on a communication path between a master module and a slave module interconnected by at least one bus B.
• the bandwidth control method can be implemented in a device Xi which will now be detailed.
• the bandwidth control device Xi comprises signal detection means, storage means, n occurrence counters and processing means configured to implement the band control method described above in parallel.
• the device Xi may also include n time counters.
• the storage means of the device Xi are provided for storing n blocking delays, n first thresholds of occurrences, n second thresholds of occurrences and / or n time thresholds.
• the storage means of the device Xi are also provided for storing n identifiers of common slave modules, and n address tables. All this information can be written to the storage means only once before the system-on-a-chip is put into service, or dynamically reconfigured.
• the storage means may for example be one or more flash memories or EEPROM.
• the invention also relates to a system-on-a-chip comprising at least one main master module Ma, at least one secondary master module M1, Mi, Mk, at least one slave module S1, Sj, Sn and a bus B connected to each module on a communication link and at least one X1 bandwidth control device,
• the bus B comprises interconnection means for communicating at least one common slave module with at least one main master module and with at least one secondary master module with at least one common road portion.
• Each bandwidth control device X1, Xi, Xk is connected to a secondary master module M1, Mk, to at least one main master Ma, and to the bus B.
• the bandwidth control device X may, as desired, be integrated in a bus, be part of a secondary master module, or may be in the form of an autonomous module placed on the link between a secondary master module and a slave port of a bus B. Each device can then be associated with a single secondary master module and block access requests from this secondary master module.
• each bandwidth control device X1, Xi, Xk associated with a respective secondary master module M1, Mi, Mk, an occurrence counter Cj, a first occurrence threshold Nj , a second occurrence threshold N ' j , a time counter and a time threshold can be assigned to a common slave module Sj present in the system-on-a-chip. In this way, any request for access to a common slave module emanating from a secondary master module can be controlled, with parameters specific to each pair formed by a secondary master module and a common slave module.
• each bandwidth control device is connected to the main master module Ma, and is intended to block requests from a respective secondary master module.
• a system may comprise several main master modules, and the slave modules are not all common slave modules.
• the bandwidth control devices can be inserted in a conventional on-chip system such as that illustrated in FIG. 1 as follows:
• a system-on-a-chip according to the invention is then obtained.

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• 2013
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