Would you laugh if I said the change is accomplished by changing only one single character?
Details here spark/core-common-lib@6.
Previous times for writing a copy of the STM32’s 128KB flash at 9MHz:
Erase 128KB in 453 ms.
Write 128KB in 1263 ms.
Read 128KB in 368 ms (128 byte blocks).
Verify sFlash read/write: pass
And at 18MHz:
Erase 128KB in 451 ms.
Write 128KB in 1048 ms.
Read 128KB in 304 ms (128 byte blocks).
Verify sFlash read/write: pass