From 21a270462e6c76e52ab4158fb503d250e5951719 Mon Sep 17 00:00:00 2001
From: Andrey Tolstoy <avtolstoy@gmail.com>
Date: Tue, 29 Nov 2016 23:12:33 +0700
Subject: [PATCH 1/2] HAL_USB_WillPreempt should return false when interrupts
 are masked

---
 hal/src/stm32f2xx/usb_hal.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/hal/src/stm32f2xx/usb_hal.c b/hal/src/stm32f2xx/usb_hal.c
index e2a353858d..7354c8a43e 100644
--- a/hal/src/stm32f2xx/usb_hal.c
+++ b/hal/src/stm32f2xx/usb_hal.c
@@ -420,6 +420,11 @@ int32_t HAL_USB_USART_Receive_Data(HAL_USB_USART_Serial serial, uint8_t peek)
 
 static bool HAL_USB_WillPreempt()
 {
+    // Ain't no one is preempting us if interrupts are currently disabled
+    if ((__get_PRIMASK() & 1)) {
+        return false;
+    }
+
     if (HAL_IsISR()) {
 #ifdef USE_USB_OTG_FS
         int32_t irq = OTG_FS_IRQn;

From 7d10df8c5b2cc49d97b4dfc084d73f6c541808af Mon Sep 17 00:00:00 2001
From: Andrey Tolstoy <avtolstoy@gmail.com>
Date: Tue, 29 Nov 2016 23:30:01 +0700
Subject: [PATCH 2/2] Test
 USBSERIAL_01_SerialDoesNotDeadlockWhenInterruptsAreMasked added1

---
 user/tests/wiring/usbserial/usbserial.cpp | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/user/tests/wiring/usbserial/usbserial.cpp b/user/tests/wiring/usbserial/usbserial.cpp
index a3eff08d65..0f45fd259a 100644
--- a/user/tests/wiring/usbserial/usbserial.cpp
+++ b/user/tests/wiring/usbserial/usbserial.cpp
@@ -22,7 +22,7 @@ void consume(Stream& serial)
     }
 }
 
-test(0_USBSERIAL_RingBufferHelperIsSane) {
+test(USBSERIAL_00_RingBufferHelperIsSane) {
     uint32_t size = 129;
     uint32_t head = 0;
     uint32_t tail = 0;
@@ -108,7 +108,19 @@ test(0_USBSERIAL_RingBufferHelperIsSane) {
     assertEqual(0, ring_space_wrapped(size, head, tail));
 }
 
-test(1_USBSERIAL_ReadWrite) {
+test(USBSERIAL_01_SerialDoesNotDeadlockWhenInterruptsAreMasked) {
+    int32_t state = HAL_disable_irq();
+    // Write 2048 + \r\n bytes into Serial TX buffer
+    for (int i = 0; i < 2048; i++) {
+        char tmp;
+        randomString(&tmp, 1);
+        Serial.write(tmp);
+    }
+    HAL_enable_irq(state);
+    Serial.println();
+}
+
+test(USBSERIAL_02_ReadWrite) {
     //The following code will test all the important USB Serial routines
     char test[] = "hello";
     char message[10];
@@ -122,7 +134,7 @@ test(1_USBSERIAL_ReadWrite) {
     assertTrue(strncmp(test, message, 5)==0);
 }
 
-test(2_USBSERIAL_isConnectedWorksCorrectly) {
+test(USBSERIAL_03_isConnectedWorksCorrectly) {
     Serial.println("Please close the USB Serial port and open it again within 60 seconds");
 
     uint32_t mil = millis();
@@ -150,7 +162,7 @@ test(2_USBSERIAL_isConnectedWorksCorrectly) {
     assertTrue(strncmp(test, message, 5)==0);
 }
 
-test(3_USBSERIAL_RxBufferFillsCompletely) {
+test(USBSERIAL_04_RxBufferFillsCompletely) {
     Serial.println("We will now test USB Serial RX buffer");
     Serial.println("Please close the USB Serial port and open it again once the device reattaches");