MCUXpresso: Update the MXRT Serial driver for MBED_TICKLESS

We should not block in case the UART is busy transmitting. The
API has been updated to check the status of all UART's and return
1 in case any of them is busy transmitting.

Signed-off-by: Mahesh Mahadevan <mahesh.mahadevan@nxp.com>

Author: mmahadevan108

targets/TARGET_NXP/TARGET_MCUXpresso_MCUS/TARGET_IMX/serial_api.c

@@ -316,14 +316,64 @@ const PinMap *serial_rts_pinmap()
     return PinMap_UART_RTS;
 }
 
-void serial_wait_tx_complete(uint32_t uart_index)
+static int serial_is_enabled(uint32_t uart_index)
 {
-    LPUART_Type *base = uart_addrs[uart_index];
+    int clock_enabled = 0;
+    switch (uart_index) {
+        case 0:
+            clock_enabled = (CCM->CCGR5 & CCM_CCGR5_CG12_MASK) >> CCM_CCGR5_CG12_SHIFT;
+            break;
+        case 1:
+            clock_enabled = (CCM->CCGR0 & CCM_CCGR0_CG14_MASK) >> CCM_CCGR0_CG14_SHIFT;
+            break;
+        case 2:
+            clock_enabled = (CCM->CCGR0 & CCM_CCGR0_CG6_MASK) >> CCM_CCGR0_CG6_SHIFT;
+            break;
+        case 3:
+            clock_enabled = (CCM->CCGR1 & CCM_CCGR1_CG12_MASK) >> CCM_CCGR1_CG12_SHIFT;
+            break;
+        case 4:
+            clock_enabled = (CCM->CCGR3 & CCM_CCGR3_CG1_MASK) >> CCM_CCGR3_CG1_SHIFT;
+            break;
+        case 5:
+            clock_enabled = (CCM->CCGR3 & CCM_CCGR3_CG3_MASK) >> CCM_CCGR3_CG3_SHIFT;
+            break;
+        case 6:
+            clock_enabled = (CCM->CCGR5 & CCM_CCGR5_CG13_MASK) >> CCM_CCGR5_CG13_SHIFT;
+            break;
+        case 7:
+            clock_enabled = (CCM->CCGR6 & CCM_CCGR6_CG7_MASK) >> CCM_CCGR6_CG7_SHIFT;
+            break;
+        default:
+            break;
+    }
+
+    return clock_enabled;
+}
+
+bool serial_check_tx_ongoing()
+{
+    LPUART_Type *base;
+    int i;
+    bool uart_tx_ongoing = false;
+
+    for (i = 0; i < FSL_FEATURE_SOC_LPUART_COUNT; i++) {
+        /* First check if UART is enabled */
+        if (!serial_is_enabled(i)) {
+            /* UART is not enabled, check the next instance */
+            continue;
+        }
+
+        base = uart_addrs[i];
 
-    /* Wait till data is flushed out of transmit buffer */
-    while (!(kLPUART_TransmissionCompleteFlag & LPUART_GetStatusFlags((LPUART_Type *)base)))
-    {
+        /* Check if data is waiting to be written out of transmit buffer */
+        if (!(kLPUART_TransmissionCompleteFlag & LPUART_GetStatusFlags((LPUART_Type *)base))) {
+            uart_tx_ongoing = true;
+            break;
+        }
     }
+
+    return uart_tx_ongoing;
 }
 
 #endif