NXP MCUXpresso: optimize us_ticker for LPC platforms

Provide new optimizations for us_ticker and wait_us.

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

targets/TARGET_NXP/TARGET_MCUXpresso_MCUS/TARGET_IMX/us_ticker.c

@@ -15,6 +15,7 @@
  */
 #include <stddef.h>
 #include "us_ticker_api.h"
+#include "us_ticker_defines.h"
 #include "fsl_pit.h"
 #include "fsl_clock_config.h"
 
@@ -85,9 +86,9 @@ void us_ticker_init(void)
  *
  * @return The current timer's counter value in ticks
  */
-uint32_t us_ticker_read()
+uint32_t (us_ticker_read)()
 {
-    return ~(PIT_GetCurrentTimerCount(PIT, kPIT_Chnl_1));
+    return us_ticker_read();
 }
 
 /** Disable us ticker interrupt

targets/TARGET_NXP/TARGET_MCUXpresso_MCUS/TARGET_IMX/us_ticker_defines.h

@@ -0,0 +1,30 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2006-2019 ARM Limited
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#ifndef _NXP_US_TICKER_DEFINES_H_
+#define _NXP_US_TICKER_DEFINES_H_
+
+#include "fsl_pit.h"
+
+#define US_TICKER_PERIOD_NUM    1
+#define US_TICKER_PERIOD_DEN    1
+
+#define US_TICKER_MASK          0xFFFFFFFF
+
+/* Macro-optimised form of us_ticker_read */
+#define us_ticker_read() (~(PIT_GetCurrentTimerCount(PIT, kPIT_Chnl_1)))
+
+#endif /* _NXP_US_TICKER_DEFINES_H_ */

targets/TARGET_NXP/TARGET_MCUXpresso_MCUS/TARGET_LPC/us_ticker.c

@@ -15,6 +15,7 @@
  */
 #include <stddef.h>
 #include "us_ticker_api.h"
+#include "us_ticker_defines.h"
 #include "fsl_ctimer.h"
 #include "PeripheralNames.h"
 
@@ -72,8 +73,9 @@ void us_ticker_init(void) {
  *
  * @return The current timer's counter value in ticks
  */
-uint32_t us_ticker_read(void) {
-    return CTIMER->TC;
+uint32_t (us_ticker_read)()
+{
+    return us_ticker_read();
 }
 
 /** Set interrupt for specified timestamp

targets/TARGET_NXP/TARGET_MCUXpresso_MCUS/TARGET_LPC/us_ticker_defines.h

@@ -0,0 +1,30 @@
+/* mbed Microcontroller Library
+ * Copyright (c) 2006-2019 ARM Limited
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+#ifndef _NXP_US_TICKER_DEFINES_H_
+#define _NXP_US_TICKER_DEFINES_H_
+
+#include "fsl_ctimer.h"
+
+#define US_TICKER_PERIOD_NUM    1
+#define US_TICKER_PERIOD_DEN    1
+
+#define US_TICKER_MASK          0xFFFFFFFF
+
+/* Macro-optimised form of us_ticker_read */
+#define us_ticker_read() (CTIMER->TC)
+
+#endif /* _NXP_US_TICKER_DEFINES_H_ */