MCUBoot Scratch possibility in EEPROM

Question

Hello, 
 I'm trying to do a bootloader with mcuboot to have an upgrade way with encryption image. My MCU is a RA6M4 with 1MB of code flash in a custom board with an 2MB EEPROM memory in QSPI. 
 So, I put MbedTLS (crypto Only) and QSPI in the stack under MCUboot port. 
 I want to use the Swap configuration with second image in EEPROM. 
 In order to avoid lose the scratch space in code flash, i'm trying to configure the scratch space inside the EEPROM. But I have error "attempting to use more internal flash than exists on the MCU". My numbers of layout is: - Bootloader Flash Area Size = 0x18000 - Image 1 Header Size = 0x200 - Image 1 Flash Area Size = 0xE8000 - Scratch Flash Area Size = 0x8000 If I put scratch flash area size to 0, the error is that i have no defined scratch area. 
 So my questions are: 
 - Is possible to put the scratch space into my external EEPROM? 
 - Can I have in my EEPROM the first MB with stuff of my aplication (littleFS) and the last MB with the second image for upgrade? 
 - Can you confirm that tinycrypt is not possible to use if I want encrypted images? I tried but shows error, I think is strange. 
 - There is any way to share functions (mainly MbedTLS crypto) between bootloader and first aplication, just to do not have same functions two times? 
 
 Thanks.

IK_Renesas · Answer

Hello David, 
 Thanks for reaching out Renesas Engineering Community. 
 As far I can understand you are facing issues with the fact that the image size is too large, and when trying to build the bootloader project you get an overflow error? Could you please send me the project to check? 
 Regarding your question if it is possible to put the scratch area space into the external memory and not into the code flash memory. 
 Generally the scratch are is an area that according to the MCUboot bootloader documentation needs to be reserved when the selected upgrade mode is swap. The reason is that you must reserve some space during the swap of the two image applications, so that if for some reason while swapping the images the MCU powers off (for example), there is an area that keeps the part of the image that has not been swapped due to the power-off. So we could say that it is a back up area for making reliable swap. 
 So theoretically yes you could reserve this scratch area into an external flash if you want to. However after taking a look in the code for the implementation of the mcuboot bootloader that has been ported into the FSP the scratch area is reserved inside the internal code flash memory by default. 
 
 So you have two options: 
 1. To edit the code of the mcuboot so that the scratch area will be reserved into the external memory. 
 2. Select an other mode like overwrite for example, but in this case you will loose the initial primary image that has been overwritten by the image stored in the external memory. 
 
 Please also check the application note we provide for booting and swapping the encrypted image from QSPI memory. 
 This picture here is a general overview of how it works: 
 
 Booting Encrypted Image using MCUboot and QSPI &ndash; Application Project 
 
 Best Regards, 
 IK