KW21Z Memory Map Inconsistency

[neal_jackson]

In the reference manual, it indicates that the KW41Z/31Z/21Z all have their RAM region start at 0x1FFF8000. The linker scripts generated for the KW21Z 256/64 when using MCUXpresso uses 0x1FFFC000 instead. Linker scripts generated for the KW41Z have RAM at the expected 0x1FFF8000. My application hits a hard fault immediately if I change this to 0x1FFF8000 as mentioned in the reference manual.

Why is this different for the KW21Z 256/64? Does this mean the amount of available RAM is less than 64KB?

Thanks for any insight you can give.

[gerardo_rodriguez]

Hello Neal Jackson,

The MKW21Z256VHT4 has 256 KB Flash and 64 KB SRAM, as indicated by Table 1-1. in the RM.

The address ranges are dependent on the size of the SRAM, where the SRAM_L region contains 1/4 of the total SRAM and the SRAM_U contains the other 3/4. So, the valid address ranges for SRAM_L and SRAM_U are then defined as:
• SRAM_L = [0x2000_0000–(SRAM_size/4)] to 0x1FFF_FFFF
• SRAM_U = 0x2000_0000 to [0x2000_0000+(SRAM_size*(3/4))-1]

Resulting in:

• SRAM_L = 0x1FFF_C000 to 0x1FFF_FFFF
• SRAM_U = 0x2000_0000 to 0x2000_BFFF

This is why MCUXpresso uses 0x1FFFC000 and will hit a hardfault if you change it to 0x1FFF8000.

Hope this helps!

Best regards,

Gerardo

[neal_jackson]

Hi Gerardo,

This makes sense, thanks for the explanation!