o add first working draft of usb version

o having bad sync problems only can use 4 bytes buffer, supper slow

poc/avr_usbload/crc.c

@@ -0,0 +1,43 @@
+#include <stdlib.h>
+#include <stdint.h> 
+
+#include "crc.h"
+#include "uart.h"
+
+extern FILE uart_stdout;
+
+uint16_t crc_xmodem_update (uint16_t crc, uint8_t data)
+{
+    int i;
+    crc = crc ^ ((uint16_t)data << 8);
+    for (i=0; i<8; i++)
+    {
+        if (crc & 0x8000)
+            crc = (crc << 1) ^ 0x1021;
+        else
+            crc <<= 1;
+    }
+
+    return crc;
+}
+
+uint16_t do_crc(uint8_t * data,uint16_t size)
+{
+	uint16_t crc =0;
+	uint16_t i;
+	for (i=0; i<size; i++){
+		crc = crc_xmodem_update(crc,data[i]);
+		//printf("%x : %x\n",crc,data[i]);	
+	}
+  	return crc;
+}
+
+
+uint16_t do_crc_update(uint16_t crc,uint8_t * data,uint16_t size)
+{
+  uint16_t i;
+  for (i=0; i<size; i++)
+	crc = crc_xmodem_update(crc,data[i]);
+  return crc;
+}
+