Problem erasing first two sectors of flash bank 0 in SAMSD32

Discussion around product based on ARM Cortex M4 core.

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humvee
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Problem erasing first two sectors of flash bank 0 in SAMSD32

Wed Oct 22, 2014 10:20 pm

Background:
We are using a SAM4SD32C processor in a hardware design that is based on the SAM4S-EK2 development board. The software consists of two independent components: a bootloader that resides in the first three flash sectors (0x00400000 to 0x0040FFFF) and the main application that uses all other sectors in flash bank 0 (0x00410000 to 0x004FFFF). The GPNVM bits are set such that we boot out of flash bank 0.

Problem:
When attempting to reflash the bootloader from the main application, we are unable to get the first two sectors to erase consistently unless we place a delay between unlocking the sectors and erasing the sectors. This delay is not necessary when erasing any other sectors, including the same first two sectors in flash bank 1. A review of the datasheet (11100E–ATARM–24-Jul-13) does not give us any indication why this situation is occurring. In fact, the datasheet states that the sector should be unlocked as soon as the call to the ROM-based IAP function returns from the command to unlock the sector (provided no error was returned, and we are not seeing any errors). Reading the lock bits via a GLB command immediately after unlocking the sectors indicates the sectors are indeed unlocked, but the delay is still necessary for these first two sectors to erase successfully.

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