diff --git a/F0:F030,F042,F072/PL2303_ringbuffer/PL2303.bin b/F0:F030,F042,F072/PL2303_ringbuffer/PL2303.bin
index 2ccd7a8..f2ab216 100755
Binary files a/F0:F030,F042,F072/PL2303_ringbuffer/PL2303.bin and b/F0:F030,F042,F072/PL2303_ringbuffer/PL2303.bin differ
diff --git a/F0:F030,F042,F072/PL2303_ringbuffer/proto.c b/F0:F030,F042,F072/PL2303_ringbuffer/proto.c
index 2e70caf..62ae31f 100644
--- a/F0:F030,F042,F072/PL2303_ringbuffer/proto.c
+++ b/F0:F030,F042,F072/PL2303_ringbuffer/proto.c
@@ -23,6 +23,7 @@
 
 extern uint32_t Tms;
 
+// 250 symbols == 1000 bit
 const char *test = "123456789A123456789B123456789C123456789D123456789E123456789F123456789G123456789H123456789I123456789J123456789K123456789L123456789M123456789N123456789O123456789P123456789Q123456789R123456789S123456789T123456789U123456789V123456789W123456789X123456789Y";
 
 char *omit_spaces(const char *buf){
@@ -198,7 +199,11 @@ const char *parse_cmd(const char *buf){
                 u3 = Tms;
                 for(int i = 0; i < 1000; ++i) USB_sendstr(test);
                 add2buf("\n\nspd=");
-                add2buf(u2str(2000000000/(Tms - u3))); add2buf("\n"); // strlen == 2Mbit, speed in bits per second
+                // strlen == 2Mbit, speed in bits per second
+                add2buf(u2str(2000000000/(Tms - u3)));
+                add2buf("\ntransfer time is ");
+                add2buf(u2str(Tms - u3));
+                add2buf("\n");
             break;
             case 'U':
                 add2buf("USB status: ");
diff --git a/F0:F030,F042,F072/PL2303_ringbuffer/usb.c b/F0:F030,F042,F072/PL2303_ringbuffer/usb.c
index e5ef3a1..bf03dd6 100644
--- a/F0:F030,F042,F072/PL2303_ringbuffer/usb.c
+++ b/F0:F030,F042,F072/PL2303_ringbuffer/usb.c
@@ -16,7 +16,15 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-// USB read/write for text or binary data through ring-buffers (mean 5187476b/s)
+// USB read/write for text or binary data through ring-buffers
+/*
+ * mean speeds (bit/s) @ buffer size (bytes):
+    5333333 @ 128
+    5249343 @ 256
+    5181347 @ 512
+    5277044 @ 2048
+    5434782 @ 4096
+*/
 
 #include "ringbuffer.h"
 #include "usb.h"
@@ -28,27 +36,26 @@ static uint8_t obuf[RBOUTSZ], ibuf[RBINSZ];
 static ringbuffer out = {.data = obuf, .length = RBOUTSZ, .head = 0, .tail = 0};
 static ringbuffer in = {.data = ibuf, .length = RBINSZ, .head = 0, .tail = 0};
 // transmission is succesfull
-static volatile uint8_t tx_succesfull = 1;
+static volatile uint8_t bufisempty = 1;
 static volatile uint8_t bufovrfl = 0;
 
 static void send_next(){
-    if(!tx_succesfull) return;
+    if(bufisempty) return;
     static int lastdsz = 0;
     int buflen = RB_read(&out, usbbuff, USB_TXBUFSZ);
     if(!buflen){
         if(lastdsz == 64) EP_Write(3, NULL, 0); // send ZLP after 64 bits packet when nothing more to send
         lastdsz = 0;
+        bufisempty = 1;
         return;
     }
-    tx_succesfull = 0;
     EP_Write(3, usbbuff, buflen);
     lastdsz = buflen;
 }
 
 // send full content of ring buffer
 int USB_sendall(){
-    while(RB_datalen(&out)){
-        send_next();
+    while(!bufisempty){
         if(!usbON) return 0;
     }
     return 1;
@@ -58,10 +65,13 @@ int USB_sendall(){
 int USB_send(const uint8_t *buf, int len){
     if(!buf || !usbON || !len) return 0;
     while(len){
-        if(tx_succesfull) send_next();
         int a = RB_write(&out, buf, len);
         len -= a;
         buf += a;
+        if(bufisempty){
+            bufisempty = 0;
+            send_next();
+        }
     }
     return 1;
 }
@@ -119,10 +129,10 @@ static void EP1_Handler(){
 
 // data IN/OUT handlers
 static void transmit_Handler(){ // EP3IN
-    tx_succesfull = 1;
     uint16_t epstatus = KEEP_DTOG_STAT(USB->EPnR[3]);
     // clear CTR keep DTOGs & STATs
     USB->EPnR[3] = (epstatus & ~(USB_EPnR_CTR_TX)); // clear TX ctr
+    send_next();
 }
 
 static void receive_Handler(){ // EP2OUT
@@ -153,6 +163,5 @@ void USB_proc(){
         break;
         default: // USB_STATE_CONNECTED - send next data portion
             if(!usbON) return;
-            if(tx_succesfull) send_next();
     }
 }
diff --git a/F0:F030,F042,F072/PL2303_ringbuffer/version.inc b/F0:F030,F042,F072/PL2303_ringbuffer/version.inc
index d4f59f2..21af120 100644
--- a/F0:F030,F042,F072/PL2303_ringbuffer/version.inc
+++ b/F0:F030,F042,F072/PL2303_ringbuffer/version.inc
@@ -1,2 +1,2 @@
-#define BUILD_NUMBER "111"
+#define BUILD_NUMBER "120"
 #define BUILD_DATE "2022-10-27"