NXP Semiconductors MPC5644A, Reference Manual, Page: 628 / 1735

Boot Assist Module (BAM)
MPC5644A Microcontroller Reference Manual, Rev. 6
628 Freescale Semiconductor
21.5.3.1 Reset boot vector
The boot vector, shown in Figure 21-5 , has to be programmed by the user to the user application code
memory device (internal or external flash) to the next 32-bit word after the RCHW. The value from this
location is used by the BAM program as a start address of the user application to switch to.
Figure 21-5. Reset boot vector
21.5.4 Internal boot mode
When the BAM program detects internal Flash boot mode, it sets up a machine check exception handler
because it will be accessing Flash memory locations that may be corrupted and cause a bus error. Then the
BAM program tries to find a valid RCHW in six predefined locations. If a valid RCHW is not found, the
BAM program proceeds to check of possibility of booting to the serial boot mode.
21.5.4.1 Finding reset configuration half word
The BAM searches the internal Flash memory for a valid reset configuration half word (RCHW). Possible
RCHW locations are shown in
Table 21-6 .
BOOT_BLOCK_ADDRESS is the address from Table 21-6 where the BAM finds a valid RCHW. If the
BAM program finds a valid RCHW, the core watchdog is enabled if the RCHW[WTE] bit is programmed
BOOT_BLOCK_A 0x0000_0004
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A15
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00
A16 A17 A18 A19 A20 A21 A22 A23 A24 A25 A26 A27 A28 A29 A30 A31
Table 21-6. Possible RCHW locations in the internal flash
Block Address
0 0x0000_0000
1 0x0000_4000
2 0x0000_8000
3 0x0000_C000
4 0x0001_0000
5 0x0001_4000
6 0x0001_8000
7 0x0001_C000
8 0x0002_0000
9 0x0003_0000