
8-30
ColdFire CF4e Core User’s Manual
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ROM Overview
The KROM controller uses the base address bits it needs and ignores lower-order bits to
support the configured KROM size, as shown in Table 8-25.
Table 8-24. ROMBAR
Field Descriptions
Bits
Name
Description
31–9
BA
Base address. Defines the ROM module base address. ROM alignment is implementation
specific. See Table 8-25.
8
WP
Write protect. Controls read/write properties of the ROM.
0 Allows read and write accesses to the SROM module
1 Allows only read accesses to the SROM module. Any attempted write reference generates an
access error exception to the ColdFire processor core.
7
D/I
Data/instruction bus. Indicates whether ROM is connected to the internal data or instruction bus.
0 Data bus
1 Instruction bus
6
—
Reserved, should be cleared.
5–1
C/I,
SC,
SD,
UC,
UD
Address space masks (AS
n
). Allows specific address spaces to be enabled or disabled, placing
internal modules in a specific address space. If an address space is disabled, an access to the
register in that address space becomes an external bus access, and the module resource is not
accessed. These bits are useful for power management as described in Section 8.6.4,
“Programming ROMBARs for Power Management.” In particular, C/I is typically set.
The address space mask bits are follows:
C/I = CPU space/interrupt acknowledge cycle mask.
Note
: C/I must be set if BA = 0.
SC = Supervisor code address space mask
SD = Supervisor data address space mask
UC = User code address space mask
UD = User data address space mask
For each AS
n
bit:
0 An access to the ROM module can occur for this address space
1 Disable this address space from the ROM module. References to this address space cannot
access the ROM module and are processed like other non-ROM references.
0
V
Valid. Indicates whether ROMBAR contents are valid. The BA value is not used and the ROM
module is not accessible until V is set.
0 Contents of ROMBAR are not valid. The ROM module is disabled.
1 Contents of ROMBAR are valid. The ROM module is enabled.
If kromvldrst. is asserted at reset, the contents of the ROMBAR are forced to 0x0000_0121. This
defines a valid ROM memory, based at address 0, write-protected with the CPU space/interrupt
acknowledge accesses masked. If kromvldrst is negated, the valid bit is cleared by reset, disabling
the ROM module.
Table 8-25. KROM Size Configuration
KROM Size Input Vector
1
KROM Size
Active Base Address Bits
Ignored Base Address Bits
0000
0 Bytes
None
31:9
0001
512 Bytes
31:9
None
0010
1 Kbytes
31:10
9
0011
2 Kbytes
31:11
10:9
0100
4 Kbytes
31:12
11:9
0101
8 Kbytes
31:13
12:9
0110
16 Kbytes
31:14
13:9
F
Freescale Semiconductor, Inc.
n
.