Maxim-integrated MAXQ622 Manual do Utilizador descarregar pdf (Página 24)

MAXQ612/MAXQ622 User’s Guide

2-20 Maxim Integrated

Next, the RAM routine calls into the flash function. Once we are executing out of flash, we can activate the DP[0] pointer

without causing a memory fault because the MMU now maps RAM into address range 0–7FFFh and ROM to higher

addresses. None of this space is MPE protected. That flash routine would look similar to this:

// this routine must be implemented in flash

ReadRAM:

push DPC

move DPC, #18h

move DP[0], A[0]

move A[0] @DP[0]

pop DPC

ret

The corresponding RAM routine looks like:

;

; No pointer activation from RAM code

;

MOVE A[0], #REQUESTED_RAM_ADDRESS

LCALL ReadRAM

2.6.4 Debugging

Note that debugging system code (including trace, break, memory dump, etc.) is disabled once memory protection

is enabled.

2.6.5 Enabling Memory Protection

Memory protection is always enabled unless the system password is empty. Utility ROM initialization code is respon-

sible for checking the password and clearing the memory protection enable (MPE) bit.

2.6.6 Reset Procedure and Setup of Memory Protection

Utility ROM code as well as system and user loader code is responsible for setting up the memory protection boundaries.

Both passwords and memory area boundary definitions are loaded from code memory. These values are part of the sys-

tem, user loader, and user application image files, and are defined when assembling or compiling the code image files.

Example for the System Image:

org 0000h

; Reset

move CP, #usr_ldr_page

move ULDR, @CP

jump sys_init

org 000Fh

user_ldr_page:

; Starting page address of user loader

dw 0020h ; Page 32

org 0010h

; System password

dw …, …, …, …

org 0020h

interrupt0:

1 2 ... 19 20 21 22 23 24 25 26 27 28 29 ... 254 255

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