Boot Assist Module (BAM)
MPC5566 Microcontroller Reference Manual, Rev. 2
16-8 Freescale Semiconductor
If the value in RCHW is valid, the watchdog timer is enabled by setting the RCHW[WTE] bit, the BAM
program fetches the reset vector from BOOT_BLOCK_ADDRESS + 0x0004, and branches to the reset
boot vector. The application must have a valid instruction at the reset boot vector address.
BOOT_BLOCK_ADDRESS + 0x0000_0004
If the watchdog timer is enabled for internal boot mode, the watchdog timeout is set to 2.5 × 2
17
system
clock cycles.
16.3.2.2 External Boot Modes
Use external boot mode to boot an application from an external asynchronous memory device that is
connected to the EBI. External boot mode is controlled by CS[0].
16.3.2.2.1 External Boot MMU Configuration
As shown in Table 16-5, the BAM program sets up two MMU regions differently than in internal flash
boot mode (refer to Table 16-2). The internal flash logical addresses are mapped to the physical addresses
of the EBI.
This allows code written to run from internal flash memory to execute from external memory.
0123456789101112131415
A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15
16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
A16A17A18A19A20A21A22A23A24A25A26A27A28A29A30A31
Figure 16-4. Reset Boot Vector
Table 16-5. MMU Configuration for External Boot Mode
TLB
Entry
Region Attributes
Logical Base
Address
Physical Base
Address
Size
1 Internal flash
memory
• Cache enabled
• Not guarded
• Big endian
• Global PID
0x0000_0000 0x2000_0000 16 MB
2 EBI • Cache enabled
• Not guarded
• Big endian
• Global PID
0x2000_0000 0x2000_0000 16 MB
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