diff --git a/stmhal/pyexec.c b/stmhal/pyexec.c
index 75709bb6a9..ecdd4d8c6d 100644
--- a/stmhal/pyexec.c
+++ b/stmhal/pyexec.c
@@ -49,7 +49,7 @@ int stdin_rx_chr(void) {
         }
 #endif
 #endif
-        if (usb_vcp_rx_any() != 0) {
+        if (usb_vcp_rx_num() != 0) {
             return usb_vcp_rx_get();
         } else if (pyb_usart_global_debug != PYB_USART_NONE && usart_rx_any(pyb_usart_global_debug)) {
             return usart_rx_char(pyb_usart_global_debug);
@@ -78,14 +78,16 @@ static const char *readline_hist[READLINE_HIST_SIZE] = {NULL, NULL, NULL, NULL,
 int readline(vstr_t *line, const char *prompt) {
     stdout_tx_str(prompt);
     int len = vstr_len(line);
-    int escape = 0;
+    int escape_seq = 0;
     int hist_num = 0;
     for (;;) {
         int c = stdin_rx_chr();
-        if (escape == 0) {
+        if (escape_seq == 0) {
             if (VCP_CHAR_CTRL_A <= c && c <= VCP_CHAR_CTRL_D && vstr_len(line) == len) {
+                // control character with empty line
                 return c;
             } else if (c == '\r') {
+                // newline
                 stdout_tx_str("\r\n");
                 for (int i = READLINE_HIST_SIZE - 1; i > 0; i--) {
                     readline_hist[i] = readline_hist[i - 1];
@@ -93,24 +95,27 @@ int readline(vstr_t *line, const char *prompt) {
                 readline_hist[0] = str_dup(vstr_str(line));
                 return 0;
             } else if (c == 27) {
-                escape = true;
+                // escape sequence
+                escape_seq = 1;
             } else if (c == 127) {
+                // backspace
                 if (vstr_len(line) > len) {
                     vstr_cut_tail(line, 1);
                     stdout_tx_str("\b \b");
                 }
             } else if (32 <= c && c <= 126) {
+                // printable character
                 vstr_add_char(line, c);
                 stdout_tx_str(line->buf + line->len - 1);
             }
-        } else if (escape == 1) {
+        } else if (escape_seq == 1) {
             if (c == '[') {
-                escape = 2;
+                escape_seq = 2;
             } else {
-                escape = 0;
+                escape_seq = 0;
             }
-        } else if (escape == 2) {
-            escape = 0;
+        } else if (escape_seq == 2) {
+            escape_seq = 0;
             if (c == 'A') {
                 // up arrow
                 if (hist_num < READLINE_HIST_SIZE && readline_hist[hist_num] != NULL) {
@@ -128,7 +133,7 @@ int readline(vstr_t *line, const char *prompt) {
                 }
             }
         } else {
-            escape = 0;
+            escape_seq = 0;
         }
         HAL_Delay(1);
     }
diff --git a/stmhal/usb.c b/stmhal/usb.c
index e6e994a0fa..21b88f9a1c 100644
--- a/stmhal/usb.c
+++ b/stmhal/usb.c
@@ -71,8 +71,8 @@ void usb_vcp_set_interrupt_char(int c) {
     }
 }
 
-int usb_vcp_rx_any(void) {
-    return USBD_CDC_RxAny();
+int usb_vcp_rx_num(void) {
+    return USBD_CDC_RxNum();
 }
 
 char usb_vcp_rx_get(void) {
diff --git a/stmhal/usb.h b/stmhal/usb.h
index a0fb153240..3e6bdccec2 100644
--- a/stmhal/usb.h
+++ b/stmhal/usb.h
@@ -11,7 +11,7 @@ void pyb_usb_dev_init(int usb_dev_type);
 bool usb_vcp_is_enabled(void);
 bool usb_vcp_is_connected(void);
 void usb_vcp_set_interrupt_char(int c);
-int usb_vcp_rx_any(void);
+int usb_vcp_rx_num(void);
 char usb_vcp_rx_get(void);
 void usb_vcp_send_str(const char* str);
 void usb_vcp_send_strn(const char* str, int len);
diff --git a/stmhal/usbd_cdc_interface.c b/stmhal/usbd_cdc_interface.c
index 49f108ffd3..e441c0b512 100644
--- a/stmhal/usbd_cdc_interface.c
+++ b/stmhal/usbd_cdc_interface.c
@@ -44,28 +44,23 @@
 
 /* Private typedef -----------------------------------------------------------*/
 /* Private define ------------------------------------------------------------*/
-#define APP_RX_DATA_SIZE  2048 // I think this must be at least CDC_DATA_FS_OUT_PACKET_SIZE
-#define APP_TX_DATA_SIZE  2048 // I think this can be any value
+#define APP_RX_DATA_SIZE  1024 // I think this must be at least CDC_DATA_FS_OUT_PACKET_SIZE (was 2048)
+#define APP_TX_DATA_SIZE  1024 // I think this can be any value (was 2048)
 
 /* Private macro -------------------------------------------------------------*/
 /* Private variables ---------------------------------------------------------*/
 
-uint8_t UserRxBuffer[APP_RX_DATA_SIZE];/* Received Data over USB are stored in this buffer */
-uint32_t UserRxBufLen; // counts number of valid characters in UserRxBuffer
+static uint8_t UserRxBuffer[APP_RX_DATA_SIZE]; // received data from USB OUT endpoint is stored in this buffer
+static uint16_t UserRxBufCur = 0; // points to next available character in UserRxBuffer
+static uint16_t UserRxBufLen = 0; // counts number of valid characters in UserRxBuffer
 
-uint8_t UserTxBuffer[APP_TX_DATA_SIZE];/* Received Data over UART (CDC interface) are stored in this buffer */
-uint32_t UserTxBufPtrIn = 0;/* Increment this pointer or roll it back to
-                               start address when data are received over USART */
-uint32_t UserTxBufPtrOut = 0; /* Increment this pointer or roll it back to
-                                 start address when data are sent over USB */
+static uint8_t UserTxBuffer[APP_TX_DATA_SIZE]; // data for USB IN endpoind is stored in this buffer
+static uint16_t UserTxBufPtrIn = 0; // increment this pointer modulo APP_TX_DATA_SIZE when new data is available
+static uint16_t UserTxBufPtrOut = 0; // increment this pointer modulo APP_TX_DATA_SIZE when data is drained
 
 static int user_interrupt_char = VCP_CHAR_NONE;
 static void *user_interrupt_data = NULL;
 
-#if 0
-/* UART handler declaration */
-UART_HandleTypeDef UartHandle;
-#endif
 /* TIM handler declaration */
 TIM_HandleTypeDef USBD_CDC_TimHandle;
 /* USB handler declaration */
@@ -145,7 +140,9 @@ static int8_t CDC_Itf_Init(void)
   /*##-5- Set Application Buffers ############################################*/
   USBD_CDC_SetTxBuffer(&hUSBDDevice, UserTxBuffer, 0);
   USBD_CDC_SetRxBuffer(&hUSBDDevice, UserRxBuffer);
-  UserRxBufLen = 0;
+
+    UserRxBufCur = 0;
+    UserRxBufLen = 0;
   
     user_interrupt_char = VCP_CHAR_NONE;
     user_interrupt_data = NULL;
@@ -357,6 +354,9 @@ static int8_t CDC_Itf_Receive(uint8_t* Buf, uint32_t *Len) {
         }
     }
 
+    // there are new characters at the start of the buffer, so point there
+    UserRxBufCur = 0;
+
     if (UserRxBufLen == 0) {
         // initiate next USB packet transfer now that UserRxBuffer has been drained
         USBD_CDC_ReceivePacket(&hUSBDDevice);
@@ -377,16 +377,19 @@ void USBD_CDC_Tx(const char *str, uint32_t len) {
     }
 }
 
-int USBD_CDC_RxAny(void) {
-    return UserRxBufLen;
+int USBD_CDC_RxNum(void) {
+    return UserRxBufLen - UserRxBufCur;
 }
 
 int USBD_CDC_RxGet(void) {
-    while (UserRxBufLen == 0) {
+    // wait for buffer to have at least 1 character in it
+    while (USBD_CDC_RxNum() == 0) {
         __WFI();
     }
-    int c = UserRxBuffer[--UserRxBufLen];
-    if (UserRxBufLen == 0) {
+
+    // get next character
+    int c = UserRxBuffer[UserRxBufCur++];
+    if (UserRxBufCur >= UserRxBufLen) {
         // initiate next USB packet transfer now that UserRxBuffer has been drained
         USBD_CDC_ReceivePacket(&hUSBDDevice);
     }
diff --git a/stmhal/usbd_cdc_interface.h b/stmhal/usbd_cdc_interface.h
index cabd68c1e0..3411893ae9 100644
--- a/stmhal/usbd_cdc_interface.h
+++ b/stmhal/usbd_cdc_interface.h
@@ -51,7 +51,7 @@ extern USBD_CDC_ItfTypeDef USBD_CDC_fops;
 
 void USBD_CDC_SetInterrupt(int chr, void *data);
 void USBD_CDC_Tx(const char *str, uint32_t len);
-int USBD_CDC_RxAny(void);
+int USBD_CDC_RxNum(void);
 int USBD_CDC_RxGet(void);
 
 /* Exported macro ------------------------------------------------------------*/