". Net Micro Framework portingkit–12" Systick Drive development

Systick drivers are important for TINYCLR, the. Net Micro framework systems are multi-threaded and multitasking (single task multithreading for managed code, but there are tasks that run concurrently with managed code, such as we ping with the Mfdeploy program TINYCLR or erase Flash, is the other task in the execution) is to rely on it to achieve.

Systick Drive has three functions, one is what we call multitasking and multithreading support, the second is to obtain the system's current tick, so as to achieve delay waiting, such as our common events_waitforevents function depends on it to achieve the delay function Three is to provide two versions of the sleep function for native code.

Compared with ARM7 or ARM9, the CORTEX-M3 series of CPUs provide systick this feature, so we do not need to use a timer to simulate the function of the tick, directly with the system to provide systick on it. CORTEX-M3 Systick Its timer count is decremented, descending to 0 will trigger the interrupt (of course to make the Tickint), and then automatically load the value of the load register, start the next counting loop.

The load register can be filled with the maximum value of 0X00FFFFFF, for the 72M CPU, there will be about 250 milliseconds of delay. Because the value of the VAL register is decremented, it is worth noting in the porting of related code that the value of the tick in our concept should be (load-val).

Add the following code in the CortexM3.h file to facilitate configuration of the Systick registers.

struct　CortexM3_SysTick
{
　　　　 static　const　UINT32　c_Base　=　0xE000E010;
　　　　 /****/　volatile　UINT32　CTRL;　//0xE000E010
　　　　 static　const　　　　UINT32　CTRL_COUNTFLAG=　((UINT32)0x00010000);
　　　　 static　const　　　　UINT32　CTRL_CLKSOURCE=　((UINT32)0x00000004);
　　　　 static　const　　　　UINT32　CTRL_TICKINT=　((UINT32)0x00000002);
　　　　 static　const　　　　UINT32　CTRL_ENABLE=　((UINT32)0x00000001);
　　　　 /****/　volatile　UINT32　LOAD;　//0xE000E014
　　　　 static　const　　　　UINT32　LOAD_RELOAD=　((UINT32)0x00FFFFFF);
　　　　 /****/　volatile　UINT32　VAL;　//0xE000E018
　　　　 static　const　　　　UINT32　VAL_CURRENT=　((UINT32)0x00FFFFFF);
　　　　 /****/　volatile　UINT32　CALIB;　//0xE000E01C
　　　　 static　const　　　　UINT32　CALIB_NOREF=　((UINT32)0x80000000);
　　　　 static　const　　　　UINT32　CALIB_SKEW=　((UINT32)0x40000000);
　　　　 static　const　　　　UINT32　CALIB_TENMS=　((UINT32)0x00FFFFFF);
};