From 2133f7cf2920d94b827f57cb34b7194b92045404 Mon Sep 17 00:00:00 2001
From: Andrew Kozlik <andrew.kozlik@gmail.com>
Date: Wed, 12 Feb 2020 17:42:47 +0100
Subject: [PATCH] core: Prevent data loss when writing to USB VCP.

---
 core/embed/firmware/mphalport.c     |  3 ++-
 core/embed/trezorhal/usb_vcp-impl.h | 18 ++++++++++++------
 2 files changed, 14 insertions(+), 7 deletions(-)

diff --git a/core/embed/firmware/mphalport.c b/core/embed/firmware/mphalport.c
index 0451805c6d..7f364f8b42 100644
--- a/core/embed/firmware/mphalport.c
+++ b/core/embed/firmware/mphalport.c
@@ -33,7 +33,8 @@ int mp_hal_stdin_rx_chr(void) {
 
 void mp_hal_stdout_tx_strn(const char *str, size_t len) {
   if (vcp_iface_num >= 0) {
-    int r = usb_vcp_write_blocking(vcp_iface_num, (const uint8_t *)str, len, 0);
+    int r =
+        usb_vcp_write_blocking(vcp_iface_num, (const uint8_t *)str, len, 500);
     (void)r;
   }
 }
diff --git a/core/embed/trezorhal/usb_vcp-impl.h b/core/embed/trezorhal/usb_vcp-impl.h
index befeb967ce..b2c11eefcc 100644
--- a/core/embed/trezorhal/usb_vcp-impl.h
+++ b/core/embed/trezorhal/usb_vcp-impl.h
@@ -297,7 +297,7 @@ int usb_vcp_write(uint8_t iface_num, const uint8_t *buf, uint32_t len) {
     b->write++;
   }
 
-  return len;
+  return i;
 }
 
 int usb_vcp_read_blocking(uint8_t iface_num, uint8_t *buf, uint32_t len,
@@ -315,13 +315,19 @@ int usb_vcp_read_blocking(uint8_t iface_num, uint8_t *buf, uint32_t len,
 int usb_vcp_write_blocking(uint8_t iface_num, const uint8_t *buf, uint32_t len,
                            int timeout) {
   uint32_t start = HAL_GetTick();
-  while (sectrue != usb_vcp_can_write(iface_num)) {
-    if (timeout >= 0 && HAL_GetTick() - start >= timeout) {
-      return 0;  // Timeout
+  uint32_t i = 0;
+  while (i < len) {
+    while (sectrue != usb_vcp_can_write(iface_num)) {
+      if (timeout >= 0 && HAL_GetTick() - start >= timeout) {
+        return i;  // Timeout
+      }
+      __WFI();  // Enter sleep mode, waiting for interrupt
     }
-    __WFI();  // Enter sleep mode, waiting for interrupt
+    int ret = usb_vcp_write(iface_num, buf + i, len - i);
+    if (ret < 0) return ret;
+    i += ret;
   }
-  return usb_vcp_write(iface_num, buf, len);
+  return i;
 }
 
 static void usb_vcp_class_init(USBD_HandleTypeDef *dev, usb_vcp_state_t *state,