lpc176x: Add initial support for LPC176x processors

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/lpc176x/timer.c

@@ -0,0 +1,59 @@
+// lpc176x timer interrupt scheduling
+//
+// Copyright (C) 2018  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include "LPC17xx.h" // LPC_TIM0
+#include "board/irq.h" // irq_disable
+#include "board/misc.h" // timer_read_time
+#include "board/timer_irq.h" // timer_dispatch_many
+#include "sched.h" // DECL_INIT
+
+// Set the next irq time
+static void
+timer_set(uint32_t value)
+{
+    LPC_TIM0->MR0 = value;
+    LPC_TIM0->IR = 0x01;
+}
+
+// Return the current time (in absolute clock ticks).
+uint32_t
+timer_read_time(void)
+{
+    return LPC_TIM0->TC;
+}
+
+// Activate timer dispatch as soon as possible
+void
+timer_kick(void)
+{
+    timer_set(timer_read_time() + 50);
+}
+
+void
+timer_init(void)
+{
+    // Disable timer
+    LPC_TIM0->TCR = 0x02;
+    // Enable interrupts
+    NVIC_SetPriority(TIMER0_IRQn, 1);
+    NVIC_EnableIRQ(TIMER0_IRQn);
+    LPC_TIM0->MCR = 0x01;
+    // Clear counter value
+    LPC_TIM0->TC = 0;
+    timer_kick();
+    // Start timer
+    LPC_TIM0->TCR = 0x01;
+}
+DECL_INIT(timer_init);
+
+void __visible __aligned(16) // aligning helps stabilize perf benchmarks
+TIMER0_IRQHandler(void)
+{
+    irq_disable();
+    uint32_t next = timer_dispatch_many();
+    timer_set(next);
+    irq_enable();
+}