Boot Assist Module (BAM)
PXN20 Microcontroller Reference Manual, Rev. 1
9-6 Freescale Semiconductor
Code type attributes for TLB entries 1–3 are set according to the coding of the user application (VLE or
classic Power Book E).
After configuring the MMU, the BAM determines the selected boot mode and provides the following
features for each of the boot modes:
9.3.3.1 Internal-Boot Mode
When the core determines that internal-boot mode has been selected, a machine check exception is
configured to handle possible ECC read errors that may occur while searching the internal flash to find the
reset configuration halfword (RCHW).
9.3.3.1.1 Reset Configuration Halfword Read
The BAM searches the internal flash memory for a valid RCHW. A valid RCHW is a 16-bit value that
contains a fixed 8-bit boot identifier and some configuration bits. The RCHW is expected to be the first
halfword in one of the low-address space small flash blocks.
The memory addresses of the six locations searched for a valid RCHW are shown in Table 9-4.
The BOOT_BLOCK_ADDRESS used in the register descriptions below is the address in Table 9-5 where
the BAM finds a valid RCHW.
2 reserved
1
0x2000_0000 0x2000_0000 256 MB Cache enabled
Not guarded
Big Endian
Global PID
3 SRAM 0x4000_0000 0x4000_0000 256 KB Cache inhibited
Not guarded
Big Endian
Global PID
1
The MMU can be programmed at this address range, but nothing responds to an access.
Table 9-4. LAS Block Memory Addresses
Block Address
0 0x0000_0000
1 0x0000_4000
4 0x0001_0000
7 0x0001_C000
8 0x0002_0000
9 0x0003_0000
Table 9-3. MMU Configuration for an Internal Boot
TLB
Entr
y
Region
Logical Base
Address
Physical Base
Address
Size Attributes
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