AHB Bus Matrix
UG0331 User Guide Revision 15.0
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7.1.3
Details of Operation
7.1.3.1
Slave Arbitration
Each of the slave devices on the AHB bus matrix contains an arbiter. Arbitration is done at two levels. At
the first level, the fixed higher priority masters are evaluated for any access request to the slave. At the
second level, the remaining busses are evaluated in round robin fashion for any access request to the
slave. The priority levels of the busses with fixed priority are listed in the following table.
The buses with round robin priority are listed in the following table.
7.1.3.1.1
Arbitration Parameters
The following slave arbitration configuration parameters are user programmable registers in the
SYSREG block.
•
Programmable slave maximum latency
: Slave maximum latency, ESRAM_MAX_LAT, decides the
peak wait time for a fixed priority master arbitrating for eSRAM access while the WRR master is
accessing the slave. After the defined latency period, the WRR master will have to re-arbitrate for
slave access. Slave maximum latency can be configurable from one to eight clock cycles (eight by
default). ESRAM_MAX_LAT is only supported for fixed priority masters addressing eSRAM slaves; it
has no effect on WRR masters. The system designer can use this feature to ensure the processor
latency for accesses to eSRAM is limited to a defined number of clock cycles. This is to facilitate
limiting the ISR latency for real-time-critical functions.
•
Programmable weight:
MASTER_WEIGHT0_CR and MASTER _WEIGHT1_CR are 5-bit
programmable registers located in the SYSREG block that define the number of consecutive
transfers the weighted master can perform without being interrupted by a fixed priority master, or
before moving onto the next master in the WRR cycle.
Table 140 •
Fixed Priority Masters
Masters
Priority
Arbitration
M3 DCode bus
MM0
1
Fixed
M3 ICode bus
MM1
2
Fixed
M3 system bus
MM2
3
Fixed
System controller
MM9
4
Fixed
Table 141 •
WRR Masters
Masters
Priority
Arbitration
HPDMA
MM3
4
WRR
FIC_0
MM4
4
WRR
FIC_1
MM5
4
WRR
MAC
MM6
4
WRR
PDMA
MM7
4
WRR
USB
MM8
4
WRR