LPC2100 series ARM7 microcontroller encryption ARM chip

1. Encryption principle description

The LPC2100 series ARM7 microcontroller is the world's first ARM chip that can be encrypted. The method of encrypting it is to set the specified data at the specified address through the user program. PHILIPS stipulates that for the LPC2100 chip (except LPC2106/2105/2104), when the data at the FLASH address 0x000001FC on the chip is 0x87654321, the chip is encrypted. After the encryption is set, the JTAG debugging interface is invalid, and the ISP function only provides the functions of reading ID and erasing the entire chip. Note: Download the program with encryption settings to the internal FLASH of the chip, and the encryption will take effect after the next system reset.

2. Encryption program implementation

In order to implement encryption settings, users must ensure that data 0x87654321 is defined at 0x000001FC. Let's first analyze the program structure with encryption settings, as shown in Figure 1. Address 0x000000~0x00000020 is the exception vector table. If the LDR instruction jump is used in the vector table, each exception service entry address can be defined between 0x00000020~0x00000040; after the exception vector table and before the 0x000001FC address, this small space can be used to write some initialization code or FIQ interrupt handler; then use NOP instructions to fill until the 0x000001FC address, define data 0x87654321 at this address, and the user's other program code follows.

Exception Vector Table

Partial initialization code

or

FIQ interrupt handling

NOP

NOP

…

DCD 0x87654321

User Code

The implementation of the encryption program is in the startup code Startup.s file of LPC2100, as shown in Listing 1. The program first uses the IF pseudo-instruction to determine whether the EN_CRP global variable has been defined. If it has been declared, the code in Listing 1 (2) to (8) is compiled to perform encryption settings. Note: The EN_CRP global variable can be predefined in the assembler or declared using GBLA/GBLL at the beginning of the file.

Program Listing 1 (2) is used to determine whether the current code address exceeds 0x000001FC. If it exceeds, the INFO pseudo-instruction is used to display an error message, see Program Listing 1 (3). Program Listing 1 (5) to (7) are used to fill NOP instructions until 0x000001FC. Program Listing 1 (8) is to define data 0x87654321 at the address 0x000001FC to implement encryption settings.

0x00000000

0x00000020

0x000001FC

Program Listing 1 LPC2100 encryption program implementation code;

Exception Vector Table

…

…

IF

EF: EN_CRP (1)

IF . >= 0x1fc (2)

INFO 1,"nThe data at 0x000001fc must be 0x87654321.nPlease delete some source before this line." (3)

ENDIF (4)

CrpData WHILE . < 0x1fc (5)

NOP (6)

WEND (7)

CrpData1 DCD 0x87654321 (8)

ENDIF (9)

3. Encryptable targets in project templates

When a project created using the LPC2100-specific project template uses the RelInFLASH target, a program with encryption settings will be generated.

For the Thumb Executable Image for UCOSII (for lpc21xx) project template, when the ThumbRelInFLASH target is selected, a program with encryption settings will be generated.