TC1796
System Units (Vol. 1 of 2)
On-Chip System Buses and Bus Bridges
User’s Manual
6-24
V2.0, 2007-07
Buses, V2.0
6.5
FPI Bus Control Units (SBCU and RBCU)
The TC1796 incorporates two BCUs: one for the SPB, called SBCU, and the other for
the RPB, called RBCU. The register name module prefix “x” of xBCU refers to the SBCU
with x = S and to the RBCU with x = R.
6.5.1
FPI Bus Arbitration
The arbitration unit of the BCU determines whether it is necessary to arbitrate for
FPI Bus ownership, and, if so, which available bus requestor gets the FPI Bus for the
next data transfer. During arbitration, the bus is granted to the requesting agent with the
highest priority. If no request is pending, the bus is granted to a default master. If no bus
master takes the bus, the BCU itself will drive the FPI Bus to prevent it from floating
electrically.
6.5.1.1
Arbitration on the System Peripheral Bus
The TC1796 SPB has five bus agents that can become a SPB bus master. Each agent
is supplied a arbitration priority as shown in
. DMA controller and OCDS agents
can be assigned to low or high priorities by software.
If there is no request from a SPB bus master, the SPB is granted to a default master
(PCP or LFI Bridge) which has been at last the default master.
6.5.1.2
Arbitration on the Remote Peripheral Bus
The TC1796 RPB has only one bus master agent, the DMA Controller. Therefore, the
RPB does not need the RBCU to arbitrate the bus, and the DMA controller is always its
default master.
Table 6-9
Priority of TC1796 SPB Bus Agents
Priority
Agent
Comment
highest
lowest
Any bus requestor meeting the starvation
protection criteria is assigned this priority
Highest priority, used only for
starvation protection
On-Chip Debug System (Cerberus),
high priority
Priority selection by software
Peripheral Control Processor
Default master 0
DMA Controller, high priority channels
Priority selection by software
LFI Bridge
Default master 1
DMA Controller, low priority channels
Priority selection by software
On-Chip Debug System (Cerberus),
low priority
Priority selection by Software