Adding buffering of TX chars

Author: nseidle

cores/arduino/ard_sup/uart/ap3_uart.cpp

@@ -119,17 +119,42 @@ size_t Uart::write(const uint8_t *buffer, size_t size)
 {
     uint32_t ui32BytesWritten = 0;
 
-    // todo: use a local buffer to guarantee lifespan of data (maybe txbuffer, but maybe not a ring buffer? b/c of efficiency + not breaking up transfers)
+    //FIFO on Apollo3 is 32 bytes
 
-    const am_hal_uart_transfer_t sUartWrite =
-        {
-            .ui32Direction = AM_HAL_UART_WRITE,
-            .pui8Data = (uint8_t *)buffer,
-            .ui32NumBytes = size,
-            .ui32TimeoutMs = AM_HAL_UART_WAIT_FOREVER,
-            .pui32BytesTransferred = (uint32_t *)&ui32BytesWritten,
-        };
-    am_hal_uart_transfer(_handle, &sUartWrite);
+    //If TX UART is sitting idle, load it. This will start the ISR TX handler as well.
+    uint32_t uartFlags = 0;
+    am_hal_uart_flags_get(_handle, &uartFlags);
+
+    // am_hal_uart_tx_flush(_handle);
+    if (uartFlags & AM_HAL_UART_FR_TX_EMPTY)
+    //if (1)
+    {
+        uint32_t amtToSend = size;
+        if (amtToSend > AM_HAL_UART_FIFO_MAX)
+            amtToSend = AM_HAL_UART_FIFO_MAX;
+
+        //Transfer to local buffer
+        uint8_t tempTX[AM_HAL_UART_FIFO_MAX];
+        for (int x = 0; x < amtToSend; x++)
+            tempTX[x] = _tx_buffer.read_char();
+
+        const am_hal_uart_transfer_t sUartWrite =
+            {
+                .ui32Direction = AM_HAL_UART_WRITE,
+                .pui8Data = (uint8_t *)buffer,
+                .ui32NumBytes = size,
+                .ui32TimeoutMs = 0, //Use non-blocking xfer
+                .pui32BytesTransferred = (uint32_t *)&ui32BytesWritten,
+            };
+        am_hal_uart_transfer(_handle, &sUartWrite);
+    }
+    else
+    {
+        //UART is already sending bytes so load the ring buffer instead
+        for (int x = 0; x < size; x++)
+            _tx_buffer.store_char(buffer[x]);
+        ui32BytesWritten = size;
+    }
     return ui32BytesWritten;
 }
 
@@ -370,9 +395,9 @@ ap3_err_t Uart::_begin(void)
 
     UARTn(_instance)->LCRH_b.FEN = 0; // Disable that pesky FIFO
 
-    // Enable RX interrupts
+    // Enable TX and RX interrupts
     NVIC_EnableIRQ((IRQn_Type)(UART0_IRQn + _instance));
-    am_hal_uart_interrupt_enable(_handle, (AM_HAL_UART_INT_RX));
+    am_hal_uart_interrupt_enable(_handle, (AM_HAL_UART_INT_RX | AM_HAL_UART_INT_TX));
     am_hal_interrupt_master_enable();
 
     // Register the class into the local list
@@ -517,6 +542,34 @@ inline void Uart::rx_isr(void)
             _rx_buffer.store_char(rx_c);
         }
     }
+
+    if (ui32Status & AM_HAL_UART_INT_TX)
+    {
+        //If bytes are sitting in TX buffer, load them into UART buffer for transfer
+        if (_tx_buffer.available())
+        {
+            uint32_t ui32BytesWritten = 0;
+
+            uint32_t amtToSend = _tx_buffer.available();
+            if (amtToSend > AM_HAL_UART_FIFO_MAX)
+                amtToSend = AM_HAL_UART_FIFO_MAX;
+
+            //Transfer to local buffer
+            uint8_t tempTX[AM_HAL_UART_FIFO_MAX];
+            for (int x = 0; x < amtToSend; x++)
+                tempTX[x] = _tx_buffer.read_char();
+
+            const am_hal_uart_transfer_t sUartWrite =
+                {
+                    .ui32Direction = AM_HAL_UART_WRITE,
+                    .pui8Data = (uint8_t *)tempTX,
+                    .ui32NumBytes = (uint32_t)amtToSend,
+                    .ui32TimeoutMs = AM_HAL_UART_WAIT_FOREVER,
+                    .pui32BytesTransferred = (uint32_t *)&ui32BytesWritten,
+                };
+            am_hal_uart_transfer(_handle, &sUartWrite);
+        }
+    }
 }
 
 // Individual ISR implementations for the two UART peripherals on the Apollo3