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4.4.8 CCI500 component

This section describes the CCI500 component.

CCI500 - about

This C++ component is a model of r0p0 of the CCI-500 Cache Coherent Interconnect for AXI4.

AXI Coherency Extensions (ACE) are extensions to AXI4. They support system-level cache-coherency between multiple clusters.

CCI500 - functionality

Some features differ in the model.

Address Decoder
  • Only supports striping down to 4KiB.
  • If the address decoder aborts the access, returns SLVERR rather than DECERR.
Interfaces
The model does not implement the Q-Channel and P-Channel interfaces.
Performance Monitoring Unit
  • PMU counters recognize only a few event sources:
    • Slave interface events:
      3ReadOnce.
      4ReadClean, ReadShared, ReadNotSharedDirty, ReadUnique.
      5MakeUnique, CleanUnique.
      6CleanInvalid, CleanShared, MakeInvalid.
      7DVM transaction received from upstream.
      9Read data that is satisfied by a snoop request.
    • No events are implemented for the global events or for the master events.
  • The PMU does not implement the event bus (EVNTBUS).
Register access
The register file only supports 32-bit accesses to its registers. Later versions of the CCI500 hardware support full write strobes to the register file. This limitation means that byte and halfword accesses work on the hardware but not on this version of the component.
Snoop filter RAMs
Snoop filter RAMs are not modelled. The Status Register fields that relate to the power state of the Snoop filter RAMs are undefined.

CCI500 - ports

This section describes the ports.

acchannelensx represents the ports ACCHANNELENS0-ACCHANNELENS6 on the RTL (Register Transfer Level) (assuming that there are seven upstream ports).

  • Each upstream ACE port y (pvbus_s[y]) has a two bit ACCHANNELENSx.
    Bit 0 == 0
    disables DVM messages from being sent to this interface.
    Bit 1 == 0
    disables snoop messages from being sent to this interface.
  • Each upstream ACE-Lite port z (pvbus_s[z]) has a one bit ACCHANNELENSx.
    Bit 0 == 0
    disables DVM messages from being sent to this interface.

The model supports various configurations with one LISA file. Each channel enable behaves as though it is one bit or two bit, as appropriate. If you send an invalid value, because of the type of the port, then the CCI model halts, producing a fatal error. Parameters set the initial values until you drive them, so if they are constant then you need not drive them.

In the RTL, the CCI500 samples the signals at reset. In the model, the CCI500 samples the signals at the first transaction. Thus any controller that produces these signals has to hold them constant for long enough.

Table 4-37 CCI500 ports

Name Protocol Type Description
acchannelensx[7] Value Slave -
evntcntoverflow[8] Signal Master -
reset_state_of_upstream_port[7] Signal Slave -
pvbus_register_file_s PVBus Slave -
pvbus_s[7] PVBus Slave -
pvbus_m[6] PVBus Master -
errirq Signal Master -
dbgen Signal Slave -
spiden Signal Slave -
spniden Signal Slave -
niden Signal Slave -
address_decoder CCI500_AddressDecoderProtocol Master -

CCI500 - parameters

This section describes the parameters.

The LISA file declares seven upstream ports. You can configure these ports with num_ace_ports and num_ace_lite_ports. The bottom num_ace_lite_ports are ACE-Lite+DVM. The next num_ace_ports are ACE. Any remaining ports are ignored; if transactions are made on them, then warnings are produced. For example, if num_ace_ports = 1 and num_ace_lite_ports = 1 then pvbus_s[1] is ACE, pvbus_s[0] is ACE-Lite+DVM and pvbus_s[6-2] are considered not to exist.

Table 4-38 CCI500 parameters

Name Type Allowed values Default value Description
cache_state_modelled bool true, false true Model the cache state.
num_ace_ports unsigned 1-4 2 The top num_ace_ports are ACE and support full coherency. The total number of ports must not exceed seven.
num_ace_lite_ports unsigned 1-6 5 The number of ACE-Lite+DVM ports. These ports are the lowest numbered ports. The total number of ports must not exceed seven.
acchannelensn uint64_t 0x0-0x3 0x3 For upstream port pvbus_s[n], where 0 <= n <= 6. Bit[0] == 0 disables DVM messages from being sent. If this port is an ACE port, then bit[1] == 0 disables snoop messages from being sent. The signal acchannelensx[n] can override this parameter. For an ACE-Lite port, bit[1] from the parameter is ignored, allowing the default value of 0x3 to create a functional system without excessive configuration.
dbgen bool true, false true Invasive debug enable. If true, enables the counting of PMU events.
spiden bool true, false true Secure invasive debug enable. If both SPIDEN and DBGEN are high, enables the counting of both Non-secure and Secure events.
spniden bool true, false true Whether Secure and Non-secure events are allowed to be counted in the performance monitor.
niden bool true, false true Whether Non-secure events are allowed to be counted in the performance monitor.
force_on_from_start bool true, false false The interconnect normally starts up with snooping disabled. This parameter allows the model to start up as enabled without programming it. This enabling is only set up at simulation reset and not at signal reset. If the upstreams can ever be held in reset, then connect the reset_state_of_upstream_port ports so that the CCI knows when to disable snoops to the upstream systems. Otherwise, the upstream system complains that it "received a snoop request while it was in reset".
reentrancy_support string - "env" Must be one of: on, off, cacheglobal, env. on: hazard checking per cache line (normal mode). off: no hazard checking (use only for single master systems). cacheglobal: hazard checking globally for cache (not per cache line, testing feature, provokes more hazards than necessary). env (or empty string): take value from FM_REENTRANCY_SUPPORT env var; if this env var is not set, use on.
number_of_phantom_entries uint64_t

0x0000000000000001-

0x00000000ffffffff

 0x0000000000000020 Number of phantom entries in the cache. Certain cache operations use phantom entries to hold temporary data. The default value is safe for all systems containing up to 32 masters.
version string - "" The version of the interconnect. Allowed versions: r0p0.
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