TC1796
System Units (Vol. 1 of 2)
LMB External Bus Unit
User’s Manual
13-34
V2.0, 2007-07
EBU, V2.0
When defining mirrored segments, the user is responsible for ensuring that there is no
collision. There is no checking mechanism in hardware that ensures that each segment
defined (either in BASE[31:28] or ALTSEG[11:8] or both) is exclusive. Therefore, the
user must ensure that each mapping from region 0 to 3 and the emulator region does not
interfere with any other; otherwise, only the mapping with the highest priority will take
effect.
Chip Select 0 Address Override Mode
The Chip Select 0 Address Override Mode is selected when bit EBU_CON.CS0FAM is
set (CS0 Fills Address Map). With CS0FAM = 1, all external bus accesses are directed
to region 0 (CS0 becomes active) and executed with the parameter settings of region 0.
This mode is automatically selected when external boot mode has been detected during
a reset (see
). In this case, the region 0 access parameters are loaded
automatically by the boot read access (see
).
Note: When performing a boot sequence from the device connected to CS0, software
must be written carefully to ensure that external code access is never
unintentionally disabled. This can be achieved when the regions are configured as
required with CS0FAM = 1 after reset, and afterwards CS0FAM is set to 0 to
activate the new address map.
Emulator Chip Select Address Override Mode
Emulator Chip Select Address Override Mode is selected when bit EBU_CON.EMUFAM
(CSEMU Fills Address Map) is set (and bit CS0FAM = 0). With EMUFAM = 1, all
external bus accesses are directed to the emulator region (CSEMU becomes active) and
executed with the parameter settings of the emulator region. This mode is automatically
selected when emulation mode has been detected during a reset (see
).
Note: When performing a boot sequence from the device connected to CSEMU,
software must be written carefully to ensure that external code access is never
unintentionally disabled. This can be achieved when all regions are configured as
required with EMUFAM = 1 after reset, and afterwards CS0FAM is set to 0 to
activate the new address map.