TC1796
System Units (Vol. 1 of 2)
LMB External Bus Unit
User’s Manual 13-20 V2.0, 2007-07
EBU, V2.0
13.4 Start-Up/Boot Process
The EBU can start up in one of three modes after a reset or boot operation.
Further details about EBU start-up mode selection after reset are defined in Table 4-3
on Page 4-12.
13.4.1 Disabled
The EBU will come up with access to the external bus disabled after reset (i.e. no access
from PLMB to external memory is possible without EBU re-configuration).
13.4.2 Emulation Mode
The Emulation Mode of the EBU allows a system to start fetching code from a region
reserved for emulator hardware. The EBU will come up with access to the external bus
enabled after reset. All accesses to the external bus are directed via the emulator region.
The fixed default configuration (contents of registers EBU_EMUBC and EBU_EMUBAP)
of the emulator region is used as a setting that will provide reasonable code execution
performance while not placing too great a restriction on the access time of the memory
device connected to the emulator region (i.e. to the CSEMU chip select output, see
Page 13-29).
In Emulation Mode, the EBU can be configured for either Arbiter or Participant arbitration
modes. When configured as Participant, the EBU must be granted the bus by an external
master before any external bus access can be made. When configured as Arbiter, the
EBU owns the bus immediately after reset and can, if required, perform immediate
external bus accesses.
Table 13-8 EBU Start-Up Modes
Start-Up Modes Arbitration Mode
Disabled
EBU is disabled
No Bus Mode
Emulation Mode
The emulator region is selected for all external bus accesses.
Participant Mode
Arbiter Mode
External Boot Mode
Region 0 is selected for all external bus accesses.
Region 0 device characteristics are auto-configured by
performing an external Boot Configuration Value fetch from a
“Standard” non-multiplexed asynchronous device (see
Page 13-21).
Participant Mode
Arbiter Mode
To Next Page
Loading...
Need help?
General