Fix UART buffering, now it works

3 files changed, 15 insertions, 8 deletions

diff --git a/app/platform/stm32f0-gcc/retarget.cpp b/app/platform/stm32f0-gcc/retarget.cpp
index a6706d3..85e12b4 100644
--- a/app/platform/stm32f0-gcc/retarget.cpp
+++ b/app/platform/stm32f0-gcc/retarget.cpp
@@ -92,6 +92,12 @@ extern "C" ssize_t read(int fd, void *buf, size_t nbytes)
     switch (file->type) {
     case FileType::kUART:
         ret = UARTRead(reinterpret_cast<UART*>(file->extra), buf, nbytes);
+        // XXX if fcntl support for disabling O_NONBLOCK will ever be added,
+        // then it has to something with this block of code
+        if (ret == 0) {
+            errno = EWOULDBLOCK;
+            ret = -1;
+        }
         break;
     case FileType::kUARTDirect:
         ret = UARTReadDirect(reinterpret_cast<UART*>(file->extra), buf, nbytes);
diff --git a/app/platform/stm32f0-gcc/ring_buffer.h b/app/platform/stm32f0-gcc/ring_buffer.h
index ae4d99d..8e6c6be 100644
--- a/app/platform/stm32f0-gcc/ring_buffer.h
+++ b/app/platform/stm32f0-gcc/ring_buffer.h
@@ -46,7 +46,7 @@ public:
     }
     constexpr size_t Occupied()
     {
-        return _head - _tail + (_head >= _tail) ? 0 : _buffer_size;
+        return _head - _tail + ((_head >= _tail) ? 0 : _buffer_size);
     }
     constexpr bool IsEmpty() { return _head == _tail; }
     constexpr bool IsFull() { return _tail + 1 == _head; }
diff --git a/app/platform/stm32f0-gcc/uart.cpp b/app/platform/stm32f0-gcc/uart.cpp
index 4d9bf5f..89472ee 100644
--- a/app/platform/stm32f0-gcc/uart.cpp
+++ b/app/platform/stm32f0-gcc/uart.cpp
@@ -42,7 +42,7 @@ UART g_uart4{
     RingBuffer<uint8_t>(g_uart4_tx_buffer, kUART4TxBufferSize),
 };
 
-static constexpr Min(size_t a, size_t b) { return (a >= b) ? a : b; }
+static constexpr Min(size_t a, size_t b) { return (a <= b) ? a : b; }
 
 size_t UARTWrite(UART* uart, const void *buf, size_t nbytes)
 {
@@ -96,19 +96,20 @@ void UARTHandleInterrupt(UART* uart)
         return;
     for (int _ = 0; _ < 256; _++) {
         const uint32_t isr = usart_regs->ISR;
-        const bool rxne = isr & USART_ISR_RXNE;
-        const bool txe = isr & USART_ISR_TXE;
-        if (!rxne && !txe)
-            break;
-        if (rxne) {
+        bool done = true;
+        if (isr & USART_ISR_RXNE) {
             uart->rx_buffer.Push(usart_regs->RDR);
+            done = false;
         }
-        if (txe) {
+        if (isr & USART_ISR_TXE) {
             if (!uart->tx_buffer.IsEmpty()) {
                 usart_regs->TDR = uart->tx_buffer.Pop();
+                done = false;
             } else {
                 usart_regs->CR1 &= ~USART_CR1_TXEIE;
             }
         }
+        if (done)
+            break;
     }
 }