RT-Thread/rt-thread — pull request #190 by bright-pan (2013-11-05 07:54:52+00:00)
Title: Fix Systick Clock bug

for the Cortex System Timer (SysTick) in cortex-m0, the timer
source clock is not SystemCoreClock, but is HCLK, in stm32f0x
refenerce mannual has the fellow description:

"The RCC feeds the Cortex System Timer (SysTick) external
clock with the AHB clock (HCLK) divided by 8. The SysTick
can work either with this clock or directly with the Cortex
clock(HCLK), configurable in the SysTick Control and Status
Register."

if SysTick Clock Source is SysTick_CLKSource_HCLK:
SysTick clock = HCLK
if SysTick Clock Source is SysTick_CLKSource_HCLK_Div8
SysTick clock = HCLK / 8