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2.5.5.21NoMatch(NOMATCH)Flag
2.6EMACControlModule
Arbiter and
bus switches
CPU
DMA Controllers
8K byte
descriptor
memory
Configuration
registers
Interrupt
logic
Single interrupt
to CPU
EMAC interrupts
MDIO interrupts
Configuration bus
Transmit and Receive
2.6.1InternalMemory
2.6.2BusArbiter
PeripheralArchitecture
ThisflagissetbytheEMACintheSOPbufferdescriptor,ifthereceivedpacketdidnotpassanyofthe
EMAC’saddressmatchcriteriaandwasnotdiscardedbecausetheRXCAFENbitwassetinthe
RXMBPENABLE.AlthoughthepacketisavalidEthernetdatapacket,itwasonlyreceivedbecausethe
EMACisinpromiscuousmode.
ThebasicfunctionsoftheEMACcontrolmodule(Figure8)aretointerfacetheEMACandMDIOmodules
totherestofthesystem,andtoprovideforalocalmemoryspacetoholdEMACpacketbufferdescriptors.
Localmemoryisusedtohelpavoidcontentiontodevicememoryspaces.Otherfunctionsincludethebus
arbiter,andinterruptlogiccontrol.
Figure8.EMACControlModuleBlockDiagram
TheEMACcontrolmoduleincludes8Kbytesofinternalmemory.Theinternalmemoryblockisessential
forallowingtheEMACtooperatemoreindependentlyoftheCPU.Italsopreventsmemoryunderflow
conditionswhentheEMACissuesreadorwriterequeststodescriptormemory.(Memoryaccessesto
readorwritetheactualEthernetpacketdataareprotectedbytheEMAC'sinternalFIFOs).
Adescriptorisa16-bytememorystructurethatholdsinformationaboutasingleEthernetpacketbuffer,
whichmaycontainafullorpartialEthernetpacket.Thuswiththe8Kmemoryblockprovidedfordescriptor
storage,theEMACmodulecansendandreceiveduptoacombined512packetsbeforeitneedstobe
servicedbyapplicationordriversoftware.
TheEMACcontrolmodulebusarbiteroperatestransparentlytotherestofthesystem.Itisused:
•ToarbitratebetweentheCPUandEMACbusesforaccesstointernaldescriptormemory.
•ToarbitratebetweeninternalEMACbusesforaccesstosystemmemory.
SPRU941A–April2007EthernetMediaAccessController(EMAC)/27
ManagementDataInput/Output(MDIO)
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