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21.5.6
Booting from the External Bus Interface (EBI)
For devices packaged in the 324-ball BGA or chip scale packages (CSP), there is an option to boot from
a memory device on the external bus. Drive the BOOTCFG0 high to select serial boot mode.
For serial boot the user needs to connect a boot memory device with a
programmed valid RCHW to the EBI.
The BAM program sets up the MMU entries for EBI and Internal Flash (see
and tries to read RCHW from logical address 0x2000_0000.
If the valid RCHW is read from that address, the BAM program reads user application code start address
from logical address 0x2000_0004, parses RCHW, sets up watchdogs, updates EBI, SRAM and Internal
Flash MMU entries, according the RCHW[VLE] bit and passes control to the user code.
If no valid RCHW was read, BAM switches to the serial boot mode.
Table 21-11. MMU Configuration for EBI Boot and Serial Boot modes
TLB
Entry
1
Internal Flash
2
21.5.6.1
EBI Configuration for External Bus Interface Boot Mode
The BAM program sets up EBI related registers as shown in
Register
EBI_MCR
EBI_BR0
EBI_OR0
SIU_PCR0
SIU_PCR[8:11]
SIU_PCR[12:27]
SIU_PCR[28:43]
Freescale Semiconductor
NOTE
Logical
Region
Base Address
0x0000_0000
EBI
0x2000_0000
Table 21-12. EBI register settings
Value
0x0000_0801
0x2000_0803
0xFF80_00F0
0x443
Selects CS[0] function, sets pad to 20 pF drive strength,
enables weak pull device for pad and enables pullup
0x440
0x40C
Selects ADDR[16:31], sets pads to medium slew rate
0x440
MPC5644A Microcontroller Reference Manual, Rev. 6
Physical
Base Address
0x2000_0000
16 Mbytes
0x2000_0000
16 Mbytes
Table
21-12.
Comments
16-bit wide bus
Burst Inhibit
Set 15 wait states, 8 MB
Selects ADDR[12:15] and sets pads to 20 pF drive
strength
and enables weak pull device for pads
Selects DATA[0:15] and sets pads to 20 pF drive
strength
Boot Assist Module (BAM)
Table
21-11), EBI bus pins
Size
Attributes
Not guarded
Big endian
Global PID
Not guarded
Big endian
Global PID
637
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