Which FlexSPI LUT entries does the Boot-ROM need for XIP?

[imxrtuser]

Hello,

in the RT1020 Reference Manual is a list of pre-defined LUT indices

The example project flexspi_nor_polling_transfer only specifies the READ LUT. In another configuration file I got from NXP support for a Macronix flash there is also the write enable LUT entry and OPI mode LUT entry specified.

1. Which of these indices does the Boot-ROM need for booting from XIP QSPI flash if you also use .configCmdEnable = 1 in nor config block? 
2. When will the Dummy command be used/for what is the Dummy command?
3. Is it somehow possible to already specify the complete needed LUT for my application in the boot config block? I have tried it but after downloading my code and checking the FlexSPI registers via debugger it looks like not all of my defined LUT entries are copied to the registers. After calling FLEXSPI_UpdateLUT in my application code everything is written to the registers as expected.

Kind regards,

Stefan

[jingpan · Accepted solution]

Hi Stefan,

1. The first 5 LUT item is used by ROM API. Since ROM API is not opened to customer, you can change them  in application. The first 2 item in LUT is read command. Other commands are not needed. Because ROM boot only use these 2 command to start NOR flash code.

2. You needn't care about it. Few SPI NOR flash has this command.

3.ROM will save all LUT items provided by user into a global variable other than load it into LUTn register directly. The first sequence of LUT register (LUT0) is always reserved as READ. 

Regards,

Jing

[imxrtuser]

Hello Jing Pan,

thank you very much for your helpful answer!

I think this is some information which would be worth to be added to the reference manual. Maybe you can forward it to the correct department.

Kind regards,

Stefan