add USB temlpate for F303

F3:F303/USB_template/main.c

@@ -0,0 +1,37 @@
+#include "hardware.h"
+#include "proto.h"
+#include "usb.h"
+
+#define MAXSTRLEN    RBINSZ
+
+volatile uint32_t Tms = 0;
+
+void sys_tick_handler(void){
+    ++Tms;
+}
+
+int main(void){
+    char inbuff[MAXSTRLEN+1];
+    if(StartHSE()){
+        SysTick_Config((uint32_t)72000); // 1ms
+    }else{
+        StartHSI();
+        SysTick_Config((uint32_t)48000); // 1ms
+    }
+    hw_setup();
+    USB_setup();
+    uint32_t ctr = Tms;
+    while(1){
+        if(Tms - ctr > 499){
+            ctr = Tms;
+            pin_toggle(GPIOB, 1 << 1 | 1 << 0); // toggle LED @ PB0
+        }
+        USB_proc();
+        int l = USB_receivestr(inbuff, MAXSTRLEN);
+        if(l < 0) USB_sendstr("ERROR: USB buffer overflow or string was too long\n");
+        else if(l){
+            const char *ans = parse_cmd(inbuff);
+            if(ans) USB_sendstr(ans);
+        }
+    }
+}