QSPI vs SPI for external memory

[RO]

Hello,

I need to interface both, an SD card and a smaller (~4Mb) external flash to the nRF52840.

The SD card will be interfaced using SPI.

For the external flash, I wanted to know which might be a better option, QSPI or SPI?

I've read a few threads like this: https://devzone.nordicsemi.com/f/nordic-q-a/33570/spi-external-flash-mx25r6435f-with-nrf52382.

Both from hardware and software perspective, is it better to have 2 SPI interfaces;  or SPI and QSPI separately?  Other criteria are ease of implementation and cost.

Very grateful for any advice,

Thanks,

Rohit

[Andy]

I guess it depends on your application.

In my application I work with 2 GB of external flash to store data while a connection isn't active. When the connection is reestablished, the data is read out from flash and sent to the client.

Since I can read data over SPI much faster than I can send it over BLE, I just used SPI. I don't really see a need to speed up the data transfer between the external flash and the NRF52, therefore no need to use QSPI. You also save some GPIOs.

However, I can imagine applications where reading (or writing) data from/to flash as fast as possible is paramount. In this case I would use QSPI.

[RO]

I guess read speed isn't of paramount importance in my application. I will have to transfer data from the external flash to the SD card though. So in this case its fine to have 2 SPI interfaces, each to SD card and external flash? 
Thanks 

[Andy]

If you can afford the GPIOs and the peripheral blocks, why not?

[CheMax]

Hello, Andy.

Can you tell (if this is not a commercial secret) what type of memory did you use? The driver for the work developed independently or taken ready?

Thank you in advance.

[Andy]

We are using some modules from Cypress Semiconductor. I developed the driver myself, but it's not a big deal to implement it if you read the datasheet carefully.