diff --git a/F3:F303/InterfaceBoard/Debug.c b/F3:F303/InterfaceBoard/Debug.c
index b19f79a..f8ad6d4 100644
--- a/F3:F303/InterfaceBoard/Debug.c
+++ b/F3:F303/InterfaceBoard/Debug.c
@@ -50,13 +50,18 @@ void debug_newline_only(){
     RB_write(&dbgrb, (const uint8_t*)&nl, 1);
 }
 
+// print by lines until there's place in USB ringbuffer
 void print_debug_messages(){
     if(!Config_mode) return;
     uint8_t rcvbuf[256];
     do{
-        int n = RB_readto(&dbgrb, '\n', rcvbuf, 256);
-        if(n == 0) break;
-        else if(n < 0) n = -n; // partial string: longer than 256 bytes
+        int l = RB_datalento(&dbgrb, '\n');
+        if(l < 1) break;
+        int freesize = USB_sendbufspace(ICFG);
+        if(freesize < l) break;
+        if(l > 256) l = 256;
+        int n = RB_read(&dbgrb, rcvbuf, l);
+        if(n < 1) break; // empty or busy
         USB_send(ICFG, rcvbuf, n);
     }while(1);
 }
diff --git a/F3:F303/InterfaceBoard/Debug.h b/F3:F303/InterfaceBoard/Debug.h
index 02ea009..aaa797b 100644
--- a/F3:F303/InterfaceBoard/Debug.h
+++ b/F3:F303/InterfaceBoard/Debug.h
@@ -32,6 +32,7 @@
 #else
 #define DBG(str)
 #define DBGs(str)
+#define DBGch(ch)
 #define DBGn()
 #define DBGpri()
 #endif
diff --git a/F3:F303/InterfaceBoard/main.c b/F3:F303/InterfaceBoard/main.c
index 2141933..55da0c0 100644
--- a/F3:F303/InterfaceBoard/main.c
+++ b/F3:F303/InterfaceBoard/main.c
@@ -45,8 +45,8 @@ int main(void){
     USBPU_OFF();
     USB_setup();
     //uint32_t ctr = Tms;
-    usb_LineCoding lc = {9600, 0, 0, 8};
-    for(int i = 0; i < 5; ++i) usart_config(i, &lc); // configure all U[S]ARTs for default data
+    //usb_LineCoding lc = {9600, 0, 0, 8};
+    //for(int i = 0; i < 5; ++i) usart_config(i, &lc); // configure all U[S]ARTs for default data
     USBPU_ON();
     while(1){
         // Put here code working WITOUT USB connected
diff --git a/F3:F303/InterfaceBoard/multiiface.bin b/F3:F303/InterfaceBoard/multiiface.bin
index 80b875d..9a2c9a7 100755
Binary files a/F3:F303/InterfaceBoard/multiiface.bin and b/F3:F303/InterfaceBoard/multiiface.bin differ
diff --git a/F3:F303/InterfaceBoard/multiiface.creator.user b/F3:F303/InterfaceBoard/multiiface.creator.user
index 36e1fe1..cb27183 100644
--- a/F3:F303/InterfaceBoard/multiiface.creator.user
+++ b/F3:F303/InterfaceBoard/multiiface.creator.user
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE QtCreatorProject>
-<!-- Written by QtCreator 18.0.2, 2026-02-16T23:57:09. -->
+<!-- Written by QtCreator 18.0.2, 2026-02-17T23:35:31. -->
 <qtcreator>
  <data>
   <variable>EnvironmentId</variable>
diff --git a/F3:F303/InterfaceBoard/proto.c b/F3:F303/InterfaceBoard/proto.c
index 08317e3..ebaee10 100644
--- a/F3:F303/InterfaceBoard/proto.c
+++ b/F3:F303/InterfaceBoard/proto.c
@@ -95,8 +95,7 @@ static const char* erpg(const char *str){
 static void sendoverU(uint8_t ifno, char *str){
     int len = strlen(str);
     CFGWR("try to send "); CFGWRn(str);
-    str[len] = '\n';
-    len = usart_send(ifno, (const uint8_t*)str, len+1);
+    len = usart_send(ifno, (const uint8_t*)str, len);
     CFGWR("sent "); CFGWR(i2str(len)); CFGWR("bytes\n");
 }
 
diff --git a/F3:F303/InterfaceBoard/ringbuffer.c b/F3:F303/InterfaceBoard/ringbuffer.c
index b0ffe8e..0750be2 100644
--- a/F3:F303/InterfaceBoard/ringbuffer.c
+++ b/F3:F303/InterfaceBoard/ringbuffer.c
@@ -15,6 +15,8 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include <string.h>
+
 #include "ringbuffer.h"
 
 static int datalen(ringbuffer *b){
@@ -24,7 +26,7 @@ static int datalen(ringbuffer *b){
 
 // stored data length
 int RB_datalen(ringbuffer *b){
-    if(b->busy) return -1;
+    if(!b || b->busy) return -1;
     b->busy = 1;
     int l = datalen(b);
     b->busy = 0;
@@ -32,7 +34,7 @@ int RB_datalen(ringbuffer *b){
 }
 
 static int hasbyte(ringbuffer *b, uint8_t byte){
-    if(b->head == b->tail) return -1; // no data in buffer
+    if(!b || b->head == b->tail) return -1; // no data in buffer
     int startidx = b->head;
     if(b->head > b->tail){ //
         for(int found = b->head; found < b->length; ++found)
@@ -51,18 +53,13 @@ static int hasbyte(ringbuffer *b, uint8_t byte){
  * @return index if found, -1 if none or busy
  */
 int RB_hasbyte(ringbuffer *b, uint8_t byte){
-    if(b->busy) return -1;
+    if(!b || b->busy) return -1;
     b->busy = 1;
     int ret = hasbyte(b, byte);
     b->busy = 0;
     return ret;
 }
 
-// poor memcpy
-static void mcpy(uint8_t *targ, const uint8_t *src, int l){
-    while(l--) *targ++ = *src++;
-}
-
 // increment head or tail
 TRUE_INLINE void incr(ringbuffer *b, volatile int *what, int n){
     *what += n;
@@ -76,9 +73,9 @@ static int read(ringbuffer *b, uint8_t *s, int len){
     int _1st = b->length - b->head;
     if(_1st > l) _1st = l;
     if(_1st > len) _1st = len;
-    mcpy(s, b->data + b->head, _1st);
+    memcpy(s, b->data + b->head, _1st);
     if(_1st < len && l > _1st){
-        mcpy(s+_1st, b->data, l - _1st);
+        memcpy(s+_1st, b->data, l - _1st);
         incr(b, &b->head, l);
         return l;
     }
@@ -94,20 +91,27 @@ static int read(ringbuffer *b, uint8_t *s, int len){
  * @return bytes read or -1 if busy
  */
 int RB_read(ringbuffer *b, uint8_t *s, int len){
-    if(b->busy) return -1;
+    if(!b || b->busy || !s || len < 1) return -1;
     b->busy = 1;
     int r = read(b, s, len);
     b->busy = 0;
     return r;
 }
 
-static int readto(ringbuffer *b, uint8_t byte, uint8_t *s, int len){
+// length of data from current position to `byte` (including byte)
+static int lento(ringbuffer *b, uint8_t byte){
     int idx = hasbyte(b, byte);
     if(idx < 0) return 0;
     int partlen = idx + 1 - b->head;
     // now calculate length of new data portion
     if(idx < b->head) partlen += b->length;
-    if(partlen > len) return -read(b, s, len);
+    return partlen;
+}
+
+static int readto(ringbuffer *b, uint8_t byte, uint8_t *s, int len){
+    int partlen = lento(b, byte);
+    if(!partlen) return 0;
+    if(partlen > len) return -1;
     return read(b, s, partlen);
 }
 
@@ -120,21 +124,29 @@ static int readto(ringbuffer *b, uint8_t byte, uint8_t *s, int len){
  * @return amount of bytes written (negative, if len<data in buffer or buffer is busy)
  */
 int RB_readto(ringbuffer *b, uint8_t byte, uint8_t *s, int len){
-    if(b->busy) return -1;
+    if(!b || b->busy || !s || len < 1) return -1;
     b->busy = 1;
     int n = readto(b, byte, s, len);
     b->busy = 0;
     return n;
 }
 
+int RB_datalento(ringbuffer *b, uint8_t byte){
+    if(!b || b->busy) return -1;
+    b->busy = 1;
+    int n = lento(b, byte);
+    b->busy = 0;
+    return n;
+}
+
 static int write(ringbuffer *b, const uint8_t *str, int l){
     int r = b->length - 1 - datalen(b); // rest length
     if(l > r || !l) return 0;
     int _1st = b->length - b->tail;
     if(_1st > l) _1st = l;
-    mcpy(b->data + b->tail, str, _1st);
+    memcpy(b->data + b->tail, str, _1st);
     if(_1st < l){ // add another piece from start
-        mcpy(b->data, str+_1st, l-_1st);
+        memcpy(b->data, str+_1st, l-_1st);
     }
     incr(b, &b->tail, l);
     return l;
@@ -148,7 +160,7 @@ static int write(ringbuffer *b, const uint8_t *str, int l){
  * @return amount of bytes written or -1 if busy
  */
 int RB_write(ringbuffer *b, const uint8_t *str, int l){
-    if(b->busy) return -1;
+    if(!b || b->busy || !str || l < 1) return -1;
     b->busy = 1;
     int w = write(b, str, l);
     b->busy = 0;
@@ -157,7 +169,7 @@ int RB_write(ringbuffer *b, const uint8_t *str, int l){
 
 // just delete all information in buffer `b`
 int RB_clearbuf(ringbuffer *b){
-    if(b->busy) return -1;
+    if(!b || b->busy) return -1;
     b->busy = 1;
     b->head = 0;
     b->tail = 0;
diff --git a/F3:F303/InterfaceBoard/ringbuffer.h b/F3:F303/InterfaceBoard/ringbuffer.h
index ed2cf95..5064755 100644
--- a/F3:F303/InterfaceBoard/ringbuffer.h
+++ b/F3:F303/InterfaceBoard/ringbuffer.h
@@ -38,4 +38,5 @@ int RB_readto(ringbuffer *b, uint8_t byte, uint8_t *s, int len);
 int RB_hasbyte(ringbuffer *b, uint8_t byte);
 int RB_write(ringbuffer *b, const uint8_t *str, int l);
 int RB_datalen(ringbuffer *b);
+int RB_datalento(ringbuffer *b, uint8_t byte);
 int RB_clearbuf(ringbuffer *b);
diff --git a/F3:F303/InterfaceBoard/usart.c b/F3:F303/InterfaceBoard/usart.c
index cf12189..c1a247a 100644
--- a/F3:F303/InterfaceBoard/usart.c
+++ b/F3:F303/InterfaceBoard/usart.c
@@ -46,7 +46,7 @@ typedef struct {
 // maybe DMA1ch2 would be for SPI1Rx (or SSI should be @ SPI3), in this case USART3 would be interrupt-driven
 // IF1[0]: USART3  APB2 72 MHz  DMA1ch2 DMA1ch3  PB14
 // IF2[1]: USART1  APB1 36 MHz  DMA1ch4 DMA1ch5  PB0
-// IF3[2]: USART2  APB2 72 MHz  DMA1ch6 DMA1ch7  PA1
+// IF3[2]: USART2  APB2 72 MHz  DMA1ch7 DMA1ch6  PA1
 // IF4[3]: UART4   APB2 72 MHz  DMA2ch5 DMA2ch3
 // IF5[4]: UART5   APB2 72 MHz  -       -       - interrupt-driven
 // IF6[5]: (CAN)
@@ -54,19 +54,20 @@ typedef struct {
 static const USART_Config UC[USARTSNO] = {
     [0] = {.instance = USART3, .pclk_freq = 36000000, .UIRQn = USART3_IRQn, .DIRQn = DMA1_Channel2_IRQn, .dma_controller = DMA1, .dma_rx_channel = DMA1_Channel3, .dma_tx_channel = DMA1_Channel2, .TTCflag = DMA_ISR_TCIF2, .DEport = GPIOB, .DEpin = 1<<14 },
     [1] = {.instance = USART1, .pclk_freq = 72000000, .UIRQn = USART1_IRQn, .DIRQn = DMA1_Channel4_IRQn, .dma_controller = DMA1, .dma_rx_channel = DMA1_Channel5, .dma_tx_channel = DMA1_Channel4, .TTCflag = DMA_ISR_TCIF4, .DEport = GPIOB, .DEpin = 1<<0  },
-    [2] = {.instance = USART2, .pclk_freq = 36000000, .UIRQn = USART2_IRQn, .DIRQn = DMA1_Channel7_IRQn, .dma_controller = DMA1, .dma_rx_channel = DMA1_Channel6, .dma_tx_channel = DMA1_Channel7, .TTCflag = DMA_ISR_TCIF7, .DEport = GPIOB, .DEpin = 1<<1  },
+    [2] = {.instance = USART2, .pclk_freq = 36000000, .UIRQn = USART2_IRQn, .DIRQn = DMA1_Channel7_IRQn, .dma_controller = DMA1, .dma_rx_channel = DMA1_Channel6, .dma_tx_channel = DMA1_Channel7, .TTCflag = DMA_ISR_TCIF7, .DEport = GPIOA, .DEpin = 1<<1  },
     [3] = {.instance = UART4,  .pclk_freq = 36000000, .UIRQn = UART4_IRQn,  .DIRQn = DMA2_Channel5_IRQn, .dma_controller = DMA2, .dma_rx_channel = DMA2_Channel3, .dma_tx_channel = DMA2_Channel5, .TTCflag = DMA_ISR_TCIF5 },
     [4] = {.instance = UART5,  .pclk_freq = 36000000, .UIRQn = UART5_IRQn }, // no DMA
 };
 
 // buffers for DMA or interrupt-driven data management
 static uint8_t  inbuffers[USARTSNO][DMARXBUFSZ];
-static uint16_t inbufidx[USARTSNO] = {0};  // for interrupt-driven - index of next character (also amount of received bytes)
+static uint16_t inbufidx[USARTSNO] = {0};       // for interrupt-driven - index of next character (also amount of received bytes)
 static uint8_t  outbuffers[USARTSNO][DMATXBUFSZ];
-static uint16_t outbufidx[USARTSNO] = {0}; // index of next char to transmit over interrupt
-static uint16_t outbuflen[USARTSNO] = {0}; // length of data to transmit over interrupt [equal 0 if nothing to send]
-static uint8_t  need2send[USARTSNO] = {0}; // flags from IDLE interrupt to send data portion
-static uint8_t  TXrdy[USARTSNO] = {1,1,1,1,1}; // TX DMA ready
+static uint16_t outbufidx[USARTSNO] = {0};      // index of next char to transmit over interrupt
+static uint16_t outbuflen[USARTSNO] = {0};      // length of data to transmit over interrupt [equal 0 if nothing to send]
+static uint8_t  need2send[USARTSNO] = {0};      // flags from IDLE interrupt to send data portion
+static uint8_t  TXrdy[USARTSNO] = {1,1,1,1,1};  // TX DMA ready
+static int      dma_read_idx[USARTSNO] = {0};   // start of data in DMA inbuffers
 // there's no way to tell recipient about overfull, so we will just "eat" spare data!
 
 
@@ -172,7 +173,7 @@ void usart_config(uint8_t ifNo, usb_LineCoding *lc){
         R->CPAR = (uint32_t) &U->RDR;
         R->CMAR = (uint32_t) inbuffers[ifNo];
         R->CNDTR = DMARXBUFSZ;
-        R->CCR = DMA_CCR_MINC | DMA_CCR_EN; // | DMA_CCR_TCIE
+        R->CCR = DMA_CCR_MINC | DMA_CCR_CIRC | DMA_CCR_EN; // manage circular buffer in polling
         // enable U[S]ART DMA
         U->CR3 = USART_CR3_DMAT | USART_CR3_DMAR;
     }else{
@@ -200,7 +201,16 @@ void usart_start(uint8_t ifNo){
     const USART_Config *cfg = &UC[ifNo];
     cfg->instance->CR1 |= USART_CR1_UE;
     NVIC_EnableIRQ(cfg->UIRQn);
-    if(cfg->dma_controller) NVIC_EnableIRQ(cfg->DIRQn);
+    if(cfg->dma_controller){ // reset Rx DMA
+        volatile DMA_Channel_TypeDef *R = cfg->dma_rx_channel;
+        dma_read_idx[ifNo] = 0;
+        R->CCR = 0;
+        R->CPAR = (uint32_t) &cfg->instance->RDR;
+        R->CMAR = (uint32_t) inbuffers[ifNo];
+        R->CNDTR = DMARXBUFSZ;
+        R->CCR = DMA_CCR_MINC | DMA_CCR_CIRC | DMA_CCR_EN;
+        NVIC_EnableIRQ(cfg->DIRQn);
+    }
     DBGch('0' + ifNo);
     DBG("U[S]ART started");
 }
@@ -213,13 +223,11 @@ void usart_stop(uint8_t ifNo){
     if(ifNo >= USARTSNO || UC[ifNo].instance == NULL) return;
     const USART_Config *cfg = &UC[ifNo];
     cfg->instance->CR1 &= ~USART_CR1_UE;
-    if(cfg->DEport) RX485(cfg->DEport, cfg->DEpin);
-    /*
     if(cfg->dma_controller){
         NVIC_DisableIRQ(cfg->DIRQn);
     }
     NVIC_DisableIRQ(cfg->UIRQn);
-    */
+    if(cfg->DEport) RX485(cfg->DEport, cfg->DEpin);
     DBGch('0' + ifNo);
     DBG("U[S]ART stopped");
 }
@@ -234,11 +242,28 @@ void usarts_process(){
         if(!(cfg->instance->CR1 & USART_CR1_UE)) continue; // USART disabled
         if(cfg->dma_controller){ // DMA-driven
             // Input data
+            int write_idx = DMARXBUFSZ - cfg->dma_rx_channel->CNDTR; // next symbol to be written
+            int available = (write_idx - dma_read_idx[i] + DMARXBUFSZ) % DMARXBUFSZ; // length of data available
+            if(need2send[i] && available == 0) need2send[i] = 0;
+            if(available >= USB_TXBUFSZ || need2send[i]){ // enough data or lonely couple of bytes
+                // copy data in one or two chunks (wrap handling)
+                if(dma_read_idx[i] + available <= DMARXBUFSZ){ // head before tail
+                    USB_send(i, &inbuffers[i][dma_read_idx[i]], available);
+                }else{ // head after tail - two chunks
+                    uint32_t first = DMARXBUFSZ - dma_read_idx[i];
+                    USB_send(i, &inbuffers[i][dma_read_idx[i]], first);
+                    USB_send(i, inbuffers[i], available - first);
+                }
+                DBG("USART -> USB over DMA");
+                dma_read_idx[i] = write_idx; // update read pointer
+            }
+#if 0
             if(DMARXBUFSZ - cfg->dma_rx_channel->CNDTR > DMARXBUFSZ/2 || need2send[i]){
                volatile DMA_Channel_TypeDef *R = cfg->dma_rx_channel;
                 R->CCR &= ~DMA_CCR_EN; // pause DMA input transactions
                 register int l = DMARXBUFSZ - R->CNDTR;
                 if(l){ // have some input data -> send and restart DMA
+                    DBG("need");
                     if(USB_send(i, inbuffers[i], l)){
                         DBG("USART -> USB over DMA");
                         // restart DMA only in case of succesfull sent or if failed, but have ability of buffer overfull
@@ -249,6 +274,7 @@ void usarts_process(){
                 }
                 R->CCR |= DMA_CCR_EN; // re-enable DMA
             }
+#endif
             // Output data
             if(TXrdy[i]){ // ready to send new data
                 int got = USB_receive(i, outbuffers[i], DMATXBUFSZ);
@@ -308,7 +334,7 @@ void usarts_process(){
 int usart_send(uint8_t ifNo, const uint8_t *data, int len){
     if(ifNo >= USARTSNO || !data || len < 1) return 0;
     const USART_Config *cfg = &UC[ifNo];
-    if(TXrdy[ifNo] == 0 || (!cfg->instance->CR1 & USART_CR1_UE)) return -1; // busy or not active
+    if(TXrdy[ifNo] == 0 || !(cfg->instance->CR1 & USART_CR1_UE)) return -1; // busy or not active
     if(len > DMATXBUFSZ) len = DMATXBUFSZ;
     memcpy(outbuffers[ifNo], data, len);
     if(cfg->dma_controller){
@@ -350,7 +376,6 @@ static void usart_isr(uint8_t ifno){
     volatile USART_TypeDef *U = cfg->instance;
     // for every flag we should also check if it's IRQ active
     if((U->ISR & USART_ISR_RXNE) && (U->CR1 & USART_CR1_RXNEIE)){ // got new byte
-        DBG("RXNE");
         if(inbufidx[ifno] == DMARXBUFSZ) (void) U->RDR; // throw away data: buffer overfull
         else inbuffers[ifno][ inbufidx[ifno]++ ] = U->RDR; // put new byte into buffer
     }
@@ -358,22 +383,17 @@ static void usart_isr(uint8_t ifno){
     if(U->ISR & USART_ISR_IDLE){ // try to send collected data (DMA-driven)
         need2send[ifno] = 1; // seems like data portion is over - try to send it
         U->ICR = USART_ICR_IDLECF;
-        DBG("IDLE");
     }
     if((U->ISR & USART_ISR_TXE) && (U->CR1 & USART_CR1_TXEIE)){ // send next byte if need (interrupt-driven)
-        DBG("TXE");
         if(outbuflen[ifno] > outbufidx[ifno]){
             U->TDR = outbuffers[ifno][ outbufidx[ifno]++ ];
         }else if(U->CR1 & USART_CR1_TXEIE){
             U->CR1 &= ~USART_CR1_TXEIE; // disable interrupt: no data to send
             TXrdy[ifno] = 1;
-            DBG("TXRDY");
         }
     }
     if(U->ISR & USART_ISR_TC){ // switch RS-485 to Rx after transmission complete
-        DBG("TC");
         if(cfg->DEport){
-            DBG("485 -> RX");
             RX485(cfg->DEport, cfg->DEpin);
             U->CR1 &= ~USART_CR1_TE;
             U->CR1 |= USART_CR1_RE;
@@ -390,7 +410,7 @@ void uart4_exti34_isr(){  usart_isr(3); }
 void uart5_exti35_isr(){  usart_isr(4); }
 
 // DMA Tx interrupts (to arm ready flag)
-void dma1_channel2_isr(){ DBG("DMA1 done"); TXrdy[0] = 1; DMA1->IFCR = DMA_IFCR_CTCIF2; }
-void dma1_channel4_isr(){ DBG("DMA2 done"); TXrdy[1] = 1; DMA1->IFCR = DMA_IFCR_CTCIF4; }
-void dma1_channel6_isr(){ DBG("DMA3 done"); TXrdy[2] = 1; DMA1->IFCR = DMA_IFCR_CTCIF6; }
-void dma2_channel5_isr(){ DBG("DMA4 done"); TXrdy[3] = 1; DMA2->IFCR = DMA_IFCR_CTCIF5; }
+void dma1_channel2_isr(){ TXrdy[0] = 1; DMA1->IFCR = DMA_IFCR_CTCIF2; }
+void dma1_channel4_isr(){ TXrdy[1] = 1; DMA1->IFCR = DMA_IFCR_CTCIF4; }
+void dma1_channel7_isr(){ TXrdy[2] = 1; DMA1->IFCR = DMA_IFCR_CTCIF7; }
+void dma2_channel5_isr(){ TXrdy[3] = 1; DMA2->IFCR = DMA_IFCR_CTCIF5; }
diff --git a/F3:F303/InterfaceBoard/usart.h b/F3:F303/InterfaceBoard/usart.h
index 1ff82b6..ad25616 100644
--- a/F3:F303/InterfaceBoard/usart.h
+++ b/F3:F303/InterfaceBoard/usart.h
@@ -22,11 +22,8 @@
 #include "usb_dev.h"
 
 // DMA linear buffers for Rx/Tx
-#define DMARXBUFSZ      128
-#define DMATXBUFSZ      128
-// ringbuffers for collected data
-#define USARTRXRBSZ     256
-#define USARTTXRBSZ     256
+#define DMARXBUFSZ      512
+#define DMATXBUFSZ      512
 
 void usart_config(uint8_t ifNo, usb_LineCoding *lc);
 void usart_start(uint8_t ifNo);
diff --git a/F3:F303/InterfaceBoard/usb_dev.c b/F3:F303/InterfaceBoard/usb_dev.c
index c063fb4..d5ff457 100644
--- a/F3:F303/InterfaceBoard/usb_dev.c
+++ b/F3:F303/InterfaceBoard/usb_dev.c
@@ -184,14 +184,11 @@ void usb_class_request(config_pack_t *req, uint8_t *data, uint16_t datalen){
     case REQ_RECIPIENT_INTERFACE:
         switch(req->bRequest){
         case SET_LINE_CODING:
-            //DBG("SLC");
             if(!data || !datalen) break; // wait for data
-            //DBG("test");
             if(datalen == sizeof(usb_LineCoding))
                 linecoding_handler(ifno, (usb_LineCoding*)data);
             break;
         case GET_LINE_CODING:
-            DBG("GLC");
             EP_WriteIRQ(0, (uint8_t*)&lineCoding[ifno], sizeof(lineCoding));
             break;
         case SET_CONTROL_LINE_STATE:
@@ -226,17 +223,26 @@ int USB_sendall(uint8_t ifno){
     return TRUE;
 }
 
+// return amount of free space in buffer
+int USB_sendbufspace(uint8_t ifno){
+    if(!CDCready[ifno]) return 0;
+    return rbout[ifno].length - RB_datalen((ringbuffer*)&rbout[ifno]);
+}
+
 // put `buf` into queue to send
 int USB_send(uint8_t ifno, const uint8_t *buf, int len){
-    if(!buf || !CDCready[ifno] || !len) return FALSE;
-    if(ifno != ICFG) DBG("USB_send");
+    if(!buf || !CDCready[ifno] || !len){
+        return FALSE;
+    }
     uint32_t T0 = Tms;
     while(len){
         if(Tms - T0 > DISCONN_TMOUT){
             //break_handler(ifno);
             return FALSE;
         }
-        if(!CDCready[ifno]) return FALSE;
+        if(!CDCready[ifno]){
+            return FALSE;
+        }
         IWDG->KR = IWDG_REFRESH;
         int l = RB_datalen((ringbuffer*)&rbout[ifno]);
         if(l < 0) continue;
@@ -255,7 +261,6 @@ int USB_send(uint8_t ifno, const uint8_t *buf, int len){
         }
     }
     if(buf[len-1] == '\n' && lastdsz[ifno] < 0){
-        if(ifno != ICFG) DBG("send_next");
         send_next(ifno);
     }
     return TRUE;
@@ -279,7 +284,6 @@ int USB_putbyte(uint8_t ifno, uint8_t byte){
     }
     // send line if got EOL
     if(byte == '\n' && lastdsz[ifno] < 0){
-        if(ifno != ICFG) DBG("send_next");
         send_next(ifno);
     }
     return TRUE;
diff --git a/F3:F303/InterfaceBoard/usb_dev.h b/F3:F303/InterfaceBoard/usb_dev.h
index eb9be56..3ea0e41 100644
--- a/F3:F303/InterfaceBoard/usb_dev.h
+++ b/F3:F303/InterfaceBoard/usb_dev.h
@@ -55,6 +55,7 @@ void linecoding_handler(uint8_t ifno, usb_LineCoding *lc);
 #define CFGWRn(s)       do{USB_sendstr(ICFG, s); USB_putbyte(ICFG, '\n');}while(0)
 #define CFGn()          USB_putbyte(ICFG, '\n')
 
+int USB_sendbufspace(uint8_t ifno);
 int USB_sendall(uint8_t ifno);
 int USB_send(uint8_t ifno, const uint8_t *buf, int len);
 int USB_putbyte(uint8_t ifno, uint8_t byte);
diff --git a/F3:F303/InterfaceBoard/version.inc b/F3:F303/InterfaceBoard/version.inc
index 2f3d46b..e22d49e 100644
--- a/F3:F303/InterfaceBoard/version.inc
+++ b/F3:F303/InterfaceBoard/version.inc
@@ -1,2 +1,2 @@
-#define BUILD_NUMBER "110"
-#define BUILD_DATE "2026-02-16"
+#define BUILD_NUMBER "140"
+#define BUILD_DATE "2026-02-17"