LPC Microcontrollers中的主题 LPC804 / ARM M0+ endianness

LPC804 / ARM M0+ endianness

bhuntingCP — Fri, 23 Dec 2022 19:34:39 GMT

Looking at the ARM docs it appears ARM M0+ could be implemented as either big endian or little endian. Which endianness for a particular implementation is left as an exercise for the silicone vendor.

I've searched high and low and cannot find a definitive answer on the endianness of NXP LPC MCUs.

I suspect the answer is little endian but I would like to see in a data book / user manual a definitive answer to the question, is the LPC804 a little endian or big endian format?

If I examine the LPC804 flash is the memory stored little or big endian?

And where do I find the explicit answer for the LPC804?

Re: LPC804 / ARM M0+ endianness

xiangjun_rong — Mon, 26 Dec 2022 02:09:14 GMT

Hi,

For the cortex-M0 core, Instruction memory and Private Peripheral Bus (PPB) accesses are always little-endian.

For the data memory, it is dependent on the implementation, but the AIRCR[ENDIANESS] Read-Only bit defines the endian format. For the LPC8xx, the bit is zero, so the data memory is little-endian.

In conclusion, the LPC804 uses little-endian format for both instruction and data memory.

I attach the UG of cortex-M0

2.1.5 Data types
The processor:
• supports the following data types:
— 32-bit words
— 16-bit halfwords
— 8-bit bytes
• manages all data memory accesses as either little-endian or big-endian,depending on the device implementation. Instruction memory and Private
Peripheral Bus (PPB) accesses are always little-endian. See Memory regions,
types and attributes on page 2-13 for more information.

Hope it can help you

XiangJUn Rong

Re: LPC804 / ARM M0+ endianness

bhuntingCP — Tue, 27 Dec 2022 14:06:02 GMT

Thank you, this fully answered my question. I did not see the answer in the LPC804 datasheet or manual. Thank you for this answer and additional user guide.