NXP Semiconductors MPC5566, Reference Manual

Page: 667 / 1268

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_A 0x0004, and branches to the reset
boot vector. The application must have a valid instruction at the reset boot vector address.
BOOT_BLOCK_A 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.
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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
A16 A17 A18 A19 A20 A21 A22 A23 A24 A25 A26 A27 A28 A29 A30 A31
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