External Flash memory size?

[thelearner]

Hello,

I am new to LoRa FUOTA and want to implement FUOTA in my SAM R34 based end node
SAM R34 has an internal memory of 256kB, so I am assuming that the maximum application size is 256kB for SAM R34 and we can use an external flash of 500kB for performing FUOTA.

So can I go with a 500kB external flash?
Does it cause any problem for FUOTA implementation

The flash I selected is  AT25DF041B

TIA

Datasheet of SAM R34
http://ww1.microchip.com/downloads/en/DeviceDoc/SAMR34-R35-Low-Power-LoRa-Sub-GHz-SiP-Data-Sheet-DS70005356B.pdf

[ataradov]

Generally you want to have more space because the images stored on the outside device would need to be encrypted, which may make them bigger than raw binary.

At the same time, it is not very likely that your application will take up all the device space and at the very least there will be some space taken up by the bootloader, so it will not be present in the application images.

Also, if you are not going to implement the protocol yourself, you may want to see what are the requirements in the existing implementations.

But yes, as a first approximation 512 kB is a good size for the external flash.

[Scrts]

General advice: use a bigger flash during development and see what's sufficient for the production application. For OTA, it's also good to have 2 images stored: new and old.

[abyrvalg]

A quick search for "lora node flash size" shows numbers in order of 64K for a loosely written firmware (HAL-based). So unless you are planning to include some heavy data like color graphics, it looks like your R34 have more than enough internal flash for an OTA buffer. That would save both material costs and development time (no need to code external flash access).