Interpretation of the partition manager report

[rtscts]

Hello,

I built peripheral_hr_coded sample and looking into the partition manager report (I trucated the output):

> west build -t partition_manager_report
  flash_primary (0x100000 - 1024kB): 
+--------------------------------------------------+
+---0x0: b0_container (0x8000 - 32kB)--------------+
| 0x0: b0 (0x8000 - 32kB)                          |
+---0x8000: s0 (0xc200 - 48kB)---------------------+
| 0x8000: s0_pad (0x200 - 512B)                    |
+---0x8200: s0_image (0xc000 - 48kB)---------------+
| 0x8200: mcuboot (0xc000 - 48kB)                  |
+--------------------------------------------------+
| 0x14200: EMPTY_0 (0x3e00 - 15kB)                 |
+---0x18000: s1 (0xc200 - 48kB)--------------------+
| 0x18000: s1_pad (0x200 - 512B)                   |
| 0x18200: EMPTY_1 (0x3e00 - 15kB)                 |
| 0x1c000: s1_image (0xc000 - 48kB)                |
+---0x28000: mcuboot_primary (0x6c000 - 432kB)-----+
| 0x28000: mcuboot_pad (0x200 - 512B)              |
+---0x28200: mcuboot_primary_app (0x6be00 - 431kB)-+
+---0x28200: spm_app (0x6be00 - 431kB)-------------+
| 0x28200: app (0x6be00 - 431kB)                   |
+--------------------------------------------------+
| 0x94000: mcuboot_secondary (0x6c000 - 432kB)     |
+--------------------------------------------------+

What are the s0_pad and s1_pad?

What are the EMPTY_0 and EMPTY_1 areas? I tried changing sizes of B0 and mcuboot partiions and these EMPTY_x areas seem to be moving around. Do they exist to fill in the gaps to make partitions aligned on the flash page boundaries? If so, is it possible to pick sizes such that there are no EMPTY_x areas?

When B0 boots mcuboot from slot 0, it prints

...
Attempting to boot from address 0x8200
...

According to the partition manager report, it is s0_image - mcuboot. It is the address I expect, so all good.

However, when B0 boots mcuboot from slot 1, it prints

...
Attempting to boot slot 1.
Attempting to boot from address 0x18200.
...

But wait, according to the partition manager report 0x18200 is EMPTY_1. One looking at the partition manager report would expect mcuboot in slot 1 us located at 0x1c000 (s1_image, 48 kB).

Nonetheless mcuboot is located at 0x18200: boot is successful.

Is this a bug in the partition manager output? Could you please explain how to interpret the output.

Thanks.

[Simon]

What are the EMPTY_0 and EMPTY_1 areas?

Let me answer the question about the empty partitions first

Take a look at Partition Manager - Configuration file format - align:dict: 

"Ensure the alignment of the start or the end of the partition by specifying a dict with a start or end key respectively, where the value is the number of bytes to align to. If necessary, empty partitions are inserted in front of or behind the partition to ensure that the alignment is correct. Only one key can be specified. Partitions that directly or indirectly (through spans) share size with the app partitions can only be aligned if they are placed directly after the app partition."

So if align is used in a pm.yml or pm_static.yml file, you might see EMPTY_ partitions in the final partition report (to make sure the alignment is correct).

 If you take a look at the file <ncs location>/bootloader/mcuboot/boot/zephyr/pm.yml you can see that the start of the partitions has to be aligned with CONFIG_FPROTECT_BLOCK_SIZE. For the nRF5340, since CONFIG_CPU_HAS_NRF_IDAU is equal to y, CONFIG_FPROTECT_BLOCK_SIZE will be equal to CONFIG_NRF_SPU_FLASH_REGION_SIZE, which is set to 0x4000 for the nRF5340. So to summarize, the start of the partitions has to be aligned with 0x4000, and empty partitions are used to achieve this.

I will answer the rest of you questions soon

Best regards,

Simon