write 1/2/3 bytes into serial flash by QSPI

[Shang Ting]

I use QSPI to access MT25qu512 serial flash and find the following behavior.

SDK: nRF5_SDK_15.3.0_59ac345

QSPI configuration:

// Use 4 bytes address from serial flash
#define QSPI_CONFIG_ADDRMODE 1
// <3=> Read4O
#define QSPI_CONFIG_READOC 3
// <2=> PP4O
#define QSPI_CONFIG_WRITEOC 2
// <0=> 32MHz
#define QSPI_CONFIG_FREQUENCY 0

write data with nrfx_qspi_write() api at address 0

1. Write 4 bytes

It is okay.

2. Write 3 bytes

system hang at nrf_qspi_event_check()

3. Write 2 bytes

system hang at nrf_qspi_event_check()

Is there any requirement of minimal byte? How can I write 1/2/3 bytes?

[haakonsh]

All memory accesses by the QSPI peripheral to external memories have to be word-aligned to the external memory's address space, and you can only read or write full words, usually 32bits(4 bytes). 

[Shang Ting]

Does it mean I have to read/write 4/8/12/... bytes?

[haakonsh]

Jupp, to addresses that are word-aligned to the external memory's address space. Ie. 0x0000, 0x0004, 0x0008, 0x000C, etc.