From cf409a54be3b3edd2b0bd3ff3e7663b4b26a764d Mon Sep 17 00:00:00 2001
From: Andrey Tolstoy <andrey@enistek.com>
Date: Tue, 7 Jun 2016 22:53:13 +0700
Subject: [PATCH] Fixes typo in USART::availableForWrite() and
 availableForWrite() behavior in general

Test SERIAL1_AvailableForWriteWorksCorrectly added to wiring/serial_loopback
---
 hal/src/core/usart_hal.c                     |  7 ++-
 hal/src/stm32f2xx/usart_hal.c                |  7 ++-
 user/tests/wiring/serial_loopback/serial.cpp | 49 ++++++++++++++++++++
 wiring/src/spark_wiring_usartserial.cpp      |  2 +-
 4 files changed, 62 insertions(+), 3 deletions(-)

diff --git a/hal/src/core/usart_hal.c b/hal/src/core/usart_hal.c
index 3a54cf92db..4a2b7b940f 100644
--- a/hal/src/core/usart_hal.c
+++ b/hal/src/core/usart_hal.c
@@ -277,7 +277,12 @@ void HAL_USART_End(HAL_USART_Serial serial)
 
 int32_t HAL_USART_Available_Data_For_Write(HAL_USART_Serial serial)
 {
-  return (unsigned int)(SERIAL_BUFFER_SIZE + usartMap[serial]->usart_tx_buffer->head - usartMap[serial]->usart_tx_buffer->tail) % SERIAL_BUFFER_SIZE;
+  int32_t tail = usartMap[serial]->usart_tx_buffer->tail;
+  int32_t available = SERIAL_BUFFER_SIZE - (usartMap[serial]->usart_tx_buffer->head >= tail ?
+    usartMap[serial]->usart_tx_buffer->head - tail :
+    (SERIAL_BUFFER_SIZE + usartMap[serial]->usart_tx_buffer->head - tail) - 1);
+
+  return available;
 }
 
 uint32_t HAL_USART_Write_Data(HAL_USART_Serial serial, uint8_t data)
diff --git a/hal/src/stm32f2xx/usart_hal.c b/hal/src/stm32f2xx/usart_hal.c
index 8e20b8ff9c..e679553f18 100644
--- a/hal/src/stm32f2xx/usart_hal.c
+++ b/hal/src/stm32f2xx/usart_hal.c
@@ -369,7 +369,12 @@ int32_t HAL_USART_Available_Data(HAL_USART_Serial serial)
 
 int32_t HAL_USART_Available_Data_For_Write(HAL_USART_Serial serial)
 {
-    return (unsigned int)(SERIAL_BUFFER_SIZE + usartMap[serial]->usart_tx_buffer->head - usartMap[serial]->usart_tx_buffer->tail) % SERIAL_BUFFER_SIZE;
+	int32_t tail = usartMap[serial]->usart_tx_buffer->tail;
+	int32_t available = SERIAL_BUFFER_SIZE - (usartMap[serial]->usart_tx_buffer->head >= tail ?
+		usartMap[serial]->usart_tx_buffer->head - tail :
+		(SERIAL_BUFFER_SIZE + usartMap[serial]->usart_tx_buffer->head - tail) - 1);
+
+	return available;
 }
 
 
diff --git a/user/tests/wiring/serial_loopback/serial.cpp b/user/tests/wiring/serial_loopback/serial.cpp
index 6083fac4af..13b25e8988 100644
--- a/user/tests/wiring/serial_loopback/serial.cpp
+++ b/user/tests/wiring/serial_loopback/serial.cpp
@@ -187,3 +187,52 @@ test(SERIAL2_ReadWriteSucceedsInLoopbackWithD0D1Shorted) {
     assertTrue(strncmp(test, message, 5)==0);
 }
 #endif
+
+test(SERIAL1_AvailableForWriteWorksCorrectly) {
+    Serial1.begin(9600);
+    assertEqual(Serial1.isEnabled(), true);
+
+    // Initially there should be SERIAL_BUFFER_SIZE available in TX buffer
+    assertEqual(Serial1.availableForWrite(), SERIAL_BUFFER_SIZE);
+
+    // Disable Serial1 IRQ to prevent it from sending data
+    NVIC_DisableIRQ(USART1_IRQn);
+    // Write (SERIAL_BUFFER_SIZE / 2) bytes into TX buffer
+    for (int i = 0; i < SERIAL_BUFFER_SIZE / 2; i++) {
+        Serial1.write('a');
+    }
+    // There should be (SERIAL_BUFFER_SIZE / 2) bytes available in TX buffer
+    assertEqual(Serial1.availableForWrite(), SERIAL_BUFFER_SIZE / 2);
+
+    // Write (SERIAL_BUFFER_SIZE / 2 - 1) bytes into TX buffer
+    for (int i = 0; i < SERIAL_BUFFER_SIZE / 2 - 1; i++) {
+        Serial1.write('b');
+    }
+    // There should only be 1 byte available in TX buffer
+    assertEqual(Serial1.availableForWrite(), 1);
+    // Enable Serial1 IRQ again to send out the data from TX buffer
+    NVIC_EnableIRQ(USART1_IRQn);
+    delay(100);
+
+    // There should be SERIAL_BUFFER_SIZE available in TX buffer again
+    assertEqual(Serial1.availableForWrite(), SERIAL_BUFFER_SIZE);
+
+    // At this point tx_buffer->head = (SERIAL_BUFFER_SIZE - 1), tx_buffer->tail = (SERIAL_BUFFER_SIZE - 1)
+    // Now test that availableForWrite() returns correct results for cases where tx_buffer->head < tx_buffer->tail
+    // Disable Serial1 IRQ again to prevent it from sending data
+    NVIC_DisableIRQ(USART1_IRQn);
+    // Write (SERIAL_BUFFER_SIZE / 2 + 1) bytes into TX buffer
+    for (int i = 0; i < SERIAL_BUFFER_SIZE / 2 + 1; i++) {
+        Serial1.write('c');
+    }
+    // There should be (SERIAL_BUFFER_SIZE / 2) bytes available in TX buffer
+    assertEqual(Serial1.availableForWrite(), SERIAL_BUFFER_SIZE / 2);
+    // Enable Serial1 IRQ again to send out the data from TX buffer
+    NVIC_EnableIRQ(USART1_IRQn);
+    delay(100);
+
+    // There should be SERIAL_BUFFER_SIZE available in TX buffer again
+    assertEqual(Serial1.availableForWrite(), SERIAL_BUFFER_SIZE);
+
+    Serial1.end();
+}
diff --git a/wiring/src/spark_wiring_usartserial.cpp b/wiring/src/spark_wiring_usartserial.cpp
index 8f356b5a35..b1d2d0e2ab 100644
--- a/wiring/src/spark_wiring_usartserial.cpp
+++ b/wiring/src/spark_wiring_usartserial.cpp
@@ -66,7 +66,7 @@ void USARTSerial::blockOnOverrun(bool block)
 
 int USARTSerial::availableForWrite(void)
 {
-  return HAL_USART_Available_Data(_serial);
+  return HAL_USART_Available_Data_For_Write(_serial);
 }
 
 int USARTSerial::available(void)