nrf51822 S110 RAM is 8K?

[qoboty]

nrf51822-QFAA has 16KB SRAM，when run with SoftDevice S110 v9.0.0, the memory areas is below:

why the size is 0x2000(8K)? when change size to 0x4000(16K), the app can not run! why this happened? where is another 8K RAM??

[Adrian Eggenberger]

The nRF51 QFAA has 16k of RAM, but the RAM must be shared between the Softdevice and your application. The S110 in your example needs 8k RAM. This is the reason your RAM section starts at 0x20002000. The area between 0x20000000 and 0x20002000 is used by your softdevice.

How much RAM a particular softdevice needs can be found in the release notes of the softdevice.