Maxim Integrated MAXQ610 - Manual (Page 21)

2-17
MAXQ610 User’s Guide
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: