riscv : add riscv qemu virt support and fix fs bit error in mstatus

ports/risc-v64/gnu/example_build/qemu_virt/trap.c

@@ -0,0 +1,46 @@
+#include "csr.h"
+#include <stdint.h>
+#include "uart.h"
+#include "hwtimer.h"
+#include "plic.h"
+#include <tx_port.h>
+#include <tx_api.h>
+
+#define OS_IS_INTERUPT(mcause)     (mcause & 0x8000000000000000ull)
+#define OS_IS_EXCEPTION(mcause)    (~(OS_IS_INTERUPT))
+#define OS_IS_TICK_INT(mcause)     (mcause == 0x8000000000000007ull)
+#define OS_IS_SOFT_INT(mcause)     (mcause == 0x8000000000000003ull)
+#define OS_IS_EXT_INT(mcause)      (mcause == 0x800000000000000bull)
+#define OS_IS_TRAP_USER(mcause)    (mcause == 0x000000000000000bull)
+extern void _tx_timer_interrupt(void);
+
+void trap_handler(uintptr_t mcause, uintptr_t mepc, uintptr_t mtval)
+{
+	if(OS_IS_INTERUPT(mcause))
+	{
+		if(OS_IS_TICK_INT(mcause))
+		{
+			hwtimer_handler();
+			_tx_timer_interrupt();
+		}
+		else if(OS_IS_EXT_INT(mcause))
+		{
+			int ret = plic_irq_intr();
+			if(ret)
+			{
+				puts("[INTERRUPT]: handler irq error!");
+				while(1) ;
+			}
+		}
+		else
+		{
+			puts("[INTERRUPT]: now can't deal with the interrupt!");
+			while(1) ;
+		}
+	}
+	else
+	{
+		puts("[EXCEPTION] : Unkown Error!!");
+		while(1) ;
+	}
+}