DSPIC33EP64GS708 datasheet(65/484 Pages) MICROCHIP

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DS70005258C-page 65

dsPIC33EPXXXGS70X/80X FAMILY

5.4

Dual Partition Flash Configuration

For dsPIC33EPXXXGS70X/80X devices operating in

Dual Partition Flash Program Memory modes, the

Inactive Partition can be erased and programmed with-

out stalling the processor. The same programming

algorithms are used for programming and erasing the

Flash in the Inactive Partition, as described in

Section 5.2 “RTSP Operation”. On top of the page

erase option, the entire Flash memory of the Inactive

Partition

can

erased

configuring

the

NVMOP<3:0> bits in the NVMCON register.

5.4.1

FLASH PARTITION SWAPPING

The Boot Sequence Number is used for determining

the Active Partition at start-up and is encoded within

the FBTSEQ Configuration register bits. Unlike most

Configuration registers, which only utilize the lower

16 bits of the program memory, FBTSEQ is a 24-bit

Configuration Word. The Boot Sequence Number

(BSEQ) is a 12-bit value and is stored in FBTSEQ

twice. The true value is stored in bits, FBTSEQ<11:0>,

and its complement is stored in bits, FBTSEQ<23:12>.

At device Reset, the sequence numbers are read and

the partition with the lowest sequence number

becomes the Active Partition. If one of the Boot

Sequence Numbers is invalid, the device will select the

partition with the valid Boot Sequence Number, or

default to Partition 1 if both sequence numbers are

invalid. See Section 27.0 “Special Features” for more

information.

The BOOTSWP instruction provides an alternative

means of swapping the Active and Inactive Partitions

(soft swap) without the need for a device Reset. The

BOOTSWP must always be followed by a GOTO instruc-

tion. The BOOTSWP instruction swaps the Active and

Inactive Partitions, and the PC vectors to the location

specified by the GOTO instruction in the newly Active

Partition.

It is important to note that interrupts should temporarily

be disabled while performing the soft swap sequence

and that after the partition swap, all peripherals and

interrupts which were enabled remain enabled. Addi-

tionally, the RAM and stack will maintain state after the

switch. As a result, it is recommended that applications

using soft swaps jump to a routine that will reinitialize

the device in order to ensure the firmware runs as

expected. The Configuration registers will have no

effect during a soft swap.

For robustness of operation, in order to execute the

BOOTSWP instruction, it is necessary to execute the

NVM unlocking sequence as follows:

Write 0x55 to NVMKEY.

Write 0xAA to NVMKEY.

Execute the BOOTSWP instruction.

If the unlocking sequence is not performed, the

BOOTSWP instruction will be executed as a forced NOP

and a GOTO instruction, following the BOOTSWP instruc-

tion, will be executed, causing the PC to jump to that

location in the current operating partition.

The SFTSWP and P2ACTIV bits in the NVMCON

Active and Inactive Partitions, as well as which partition

is active. After the BOOTSWP and GOTO instructions, the

SFTSWP bit should be polled to verify the partition

swap has occurred and then cleared for the next panel

swap event.

5.4.2

DUAL PARTITION MODES

While operating in Dual Partition mode, the

dsPIC33EPXXXGS70X/80X family devices have the

option for both partitions to have their own defined

security segments, as shown in Figure 27-4. Alterna-

tively, the device can operate in Protected Dual Partition

mode, where Partition 1 becomes permanently erase/

write-protected. Protected Dual Partition mode allows for

a “Factory Default” mode, which provides a fail-safe

backup image to be stored in Partition 1.

dsPIC33EPXXXGS70X/80X family devices can also

operate in Privileged Dual Partition mode, where addi-

tional security protections are implemented to allow for

protection of intellectual property when multiple parties

have software within the device. In Privileged Dual Par-

tition mode, both partitions place additional restrictions

on the FBSLIM register. These prevent changes to the

size of the Boot Segment and General Segment,

ensuring that neither segment will be altered.

5.5

Flash Memory Resources

Many useful resources are provided on the main

product page of the Microchip website for the devices

listed in this data sheet. This product page contains the

latest updates and additional information.

5.5.1

KEY RESOURCES

• “Dual Partition Flash Program Memory”

(DS70005156) in the “dsPIC33/PIC24 Family

Reference Manual”

• Code Samples

• Application Notes

• Software Libraries

• Webinars

• All Related “dsPIC33/PIC24 Family Reference

Manual” Sections

• Development Tools

Note 1: The application software to be loaded

into the Inactive Partition will have the

address of the Active Partition. The

bootloader firmware will need to offset

the address by 0x400000 in order to write

to the Inactive Partition.

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