OpenCellular/core/cortex-m/task.c

/* Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

/* Task scheduling / events module for Chrome EC operating system */

#include "config.h"
#include "atomic.h"
#include "console.h"
#include "cpu.h"
#include "link_defs.h"
#include "task.h"
#include "timer.h"
#include "uart.h"
#include "util.h"

/**
 * Global memory size for a task : 512 bytes
 * including its contexts and its stack
 */
#define TASK_SIZE_LOG2 9
#define TASK_SIZE      (1<<TASK_SIZE_LOG2)

typedef union {
	struct {
		uint32_t sp;       /* saved stack pointer for context switch */
		uint32_t events;   /* bitmaps of received events */
		uint64_t runtime;  /* Time spent in task */
		uint32_t guard;    /* Guard value to detect stack overflow */
		uint8_t stack[0];  /* task stack */
	};
	uint32_t context[TASK_SIZE/4];
} task_;

#define CONTEXT_SP      (__builtin_offsetof(task_, sp) / sizeof(uint32_t))
#define CONTEXT_GUARD   (__builtin_offsetof(task_, guard) / sizeof(uint32_t))

/* declare task routine prototypes */
#define TASK(n, r, d) int r(void *);
#include TASK_LIST
static void __idle(void);
CONFIG_TASK_LIST
#undef TASK

/* store the task names for easier debugging */
#define TASK(n, r, d)  #n,
#include TASK_LIST
static const char * const task_names[] = {
	"<< idle >>",
	CONFIG_TASK_LIST
};
#undef TASK


#ifdef CONFIG_TASK_PROFILING
static uint64_t task_start_time; /* Time task scheduling started */
static uint64_t exc_start_time;  /* Time of task->exception transition */
static uint64_t exc_end_time;    /* Time of exception->task transition */
static uint64_t exc_total_time;  /* Total time in exceptions */
static uint32_t svc_calls;       /* Service calls */
static uint32_t irq_dist[CONFIG_IRQ_COUNT];  /* Distribution of IRQ calls */
#endif

extern void __switchto(task_ *from, task_ *to);
extern int __task_start(int *need_resched);

/* Idle task.  Executed when no tasks are ready to be scheduled. */
void __idle(void)
{
	while (1) {
		/* Wait for the irq event */
		asm("wfi");
		/* TODO: more power management here */
	}
}


static void task_exit_trap(void)
{
	int i = task_get_current();
	uart_printf("[Task %d (%s) exited!]\n", i, task_names[i]);
	/* Exited tasks simply sleep forever */
	while (1)
		task_wait_event(-1);
}


#define GUARD_VALUE 0x12345678

/* Declare and fill the contexts for all tasks. Note that while it would be
 * more readable to use the struct fields (.sp, .guard) where applicable, gcc
 * can't mix initializing some fields on one side of the union and some fields
 * on the other, so we have to use .context for all initialization. */
#define TASK(n, r, d)  {						\
	.context[CONTEXT_SP] = (uint32_t)(tasks + TASK_ID_##n + 1) - 64,\
	.context[CONTEXT_GUARD] = GUARD_VALUE,				\
	.context[TASK_SIZE/4 - 8/*r0*/] = (uint32_t)d,                  \
	.context[TASK_SIZE/4 - 3/*lr*/] = (uint32_t)task_exit_trap,     \
	.context[TASK_SIZE/4 - 2/*pc*/] = (uint32_t)r,                  \
	.context[TASK_SIZE/4 - 1/*psr*/] = 0x01000000 },
#include TASK_LIST
static task_ tasks[] __attribute__((section(".data.tasks")))
		__attribute__((aligned(TASK_SIZE))) = {
	TASK(IDLE, __idle, 0)
	CONFIG_TASK_LIST
};
#undef TASK
/* Reserve space to discard context on first context switch. */
uint32_t scratchpad[17] __attribute__((section(".data.tasks")));

/* Has task context switching been enabled? */
/* TODO: (crosbug.com/p/9274) this currently gets enabled at tast start time
 * and never cleared.  We should optimize when we need to call svc_handler()
 * so we don't waste time calling it if we're not profiling and no event has
 * occurred. */
static int need_resched = 0;

/**
 * bitmap of all tasks ready to be run
 *
 * Currently all tasks are enabled at startup.
 */
static uint32_t tasks_ready = (1<<TASK_ID_COUNT) - 1;


static task_ *__get_current(void)
{
	unsigned sp;

	asm("mov %0, sp":"=r"(sp));
	return (task_ *)((sp - 4) & ~(TASK_SIZE-1));
}


/**
 * Return a pointer to the task preempted by the current exception
 *
 * designed to be called from interrupt context.
 */
static task_ *__get_task_scheduled(void)
{
	unsigned sp;

	asm("mrs %0, psp":"=r"(sp));
	return (task_ *)((sp - 16) & ~(TASK_SIZE-1));
}


static inline task_ *__task_id_to_ptr(task_id_t id)
{
	return tasks + id;
}


void interrupt_disable(void)
{
	asm("cpsid i");
}


void interrupt_enable(void)
{
	asm("cpsie i");
}


inline int in_interrupt_context(void)
{
	int ret;
	asm("mrs %0, ipsr \n"             /* read exception number */
	    "lsl %0, #23  \n":"=r"(ret)); /* exception bits are the 9 LSB */
	return ret;
}


inline int get_interrupt_context(void)
{
	int ret;
	asm("mrs %0, ipsr \n":"=r"(ret)); /* read exception number */
	return ret & 0x1ff;                /* exception bits are the 9 LSB */
}


task_id_t task_get_current(void)
{
	task_id_t id = __get_current() - tasks;
	if (id >= TASK_ID_COUNT)
		id = TASK_ID_INVALID;

	return id;
}


uint32_t *task_get_event_bitmap(task_id_t tskid)
{
	task_ *tsk = __task_id_to_ptr(tskid);
	return &tsk->events;
}


/**
 * scheduling system call
 */
void svc_handler(int desched, task_id_t resched)
{
	task_ *current, *next;
#ifdef CONFIG_TASK_PROFILING
	int exc = get_interrupt_context();
	uint64_t t;
#endif

	/* Push the priority to -1 until the return, to avoid being
	 * interrupted */
	asm volatile("cpsid f\n"
		     "isb\n");

#ifdef CONFIG_TASK_PROFILING
	/* SVCall isn't triggered via DECLARE_IRQ(), so it needs to track its
	 * start time explicitly. */
	if (exc == 0xb) {
		exc_start_time = get_time().val;
		svc_calls++;
	}
#endif

	current = __get_task_scheduled();
#ifdef CONFIG_OVERFLOW_DETECT
	ASSERT(current->guard == GUARD_VALUE);
#endif

	if (desched && !current->events) {
		/* Remove our own ready bit */
		tasks_ready &= ~(1 << (current-tasks));
	}
	tasks_ready |= 1 << resched;

	ASSERT(tasks_ready);
	next = __task_id_to_ptr(31 - __builtin_clz(tasks_ready));

#ifdef CONFIG_TASK_PROFILING
	/* Track time in interrupts */
	t = get_time().val;
	exc_total_time += (t - exc_start_time);

	/* Bill the current task for time between the end of the last interrupt
	 * and the start of this one. */
	current->runtime += (exc_start_time - exc_end_time);
	exc_end_time = t;
#endif

	/* Nothing to do */
	if (next == current)
		return;

	__switchto(current, next);
}


void __schedule(int desched, int resched)
{
	register int p0 asm("r0") = desched;
	register int p1 asm("r1") = resched;
	/* TODO remove hardcoded opcode
	 * SWI not compiled properly for ARMv7-M on our current chroot toolchain
	 */
	asm(".hword 0xdf00 @swi 0"::"r"(p0),"r"(p1));
}


#ifdef CONFIG_TASK_PROFILING
void task_start_irq_handler(void *excep_return)
{
	/* Get time before checking depth, in case this handler is
	 * pre-empted */
	uint64_t t = get_time().val;
	int irq = get_interrupt_context() - 16;

	/* Track IRQ distribution.  No need for atomic add, because an IRQ
	* can't pre-empt itself. */
	if (irq < ARRAY_SIZE(irq_dist))
		irq_dist[irq]++;

	/* Continue iff a rescheduling event happened and we are not called
	 * from another exception (this must match the logic for when we chain
	 * to svc_handler() below). */
	if (!need_resched || (((uint32_t)excep_return & 0xf) == 1))
		return;

	exc_start_time = t;
}
#endif


void task_resched_if_needed(void *excep_return)
{
	/* Continue iff a rescheduling event happened and we are not called
	 * from another exception. */
	if (!need_resched || (((uint32_t)excep_return & 0xf) == 1))
		return;

	svc_handler(0, 0);
}


static uint32_t __wait_evt(int timeout_us, task_id_t resched)
{
	task_ *tsk = __get_current();
	task_id_t me = tsk - tasks;
	uint32_t evt;
	int ret;

	ASSERT(!in_interrupt_context());

	if (timeout_us > 0) {
		timestamp_t deadline = get_time();
		deadline.val += timeout_us;
		ret = timer_arm(deadline, me);
		ASSERT(ret == EC_SUCCESS);
	}
	while (!(evt = atomic_read_clear(&tsk->events)))
	{
		/* Remove ourself and get the next task in the scheduler */
		__schedule(1, resched);
		resched = TASK_ID_IDLE;
	}
	if (timeout_us > 0)
		timer_cancel(me);
	return evt;
}


uint32_t task_set_event(task_id_t tskid, uint32_t event, int wait)
{
	task_ *receiver = __task_id_to_ptr(tskid);
	ASSERT(receiver);

	/* set the event bit in the receiver message bitmap */
	atomic_or(&receiver->events, event);

	/* Re-schedule if priorities have changed */
	if (in_interrupt_context()) {
		/* the receiver might run again */
		atomic_or(&tasks_ready, 1 << tskid);
	} else {
		if (wait)
			return __wait_evt(-1, tskid);
		else
			__schedule(0, tskid);
	}

	return 0;
}


uint32_t task_wait_event(int timeout_us)
{
	return __wait_evt(timeout_us, TASK_ID_IDLE);
}


void task_enable_irq(int irq)
{
	CPU_NVIC_EN(irq / 32) = 1 << (irq % 32);
}


void task_disable_irq(int irq)
{
	CPU_NVIC_DIS(irq / 32) = 1 << (irq % 32);
}


void task_clear_pending_irq(int irq)
{
	CPU_NVIC_UNPEND(irq / 32) = 1 << (irq % 32);
}


void task_trigger_irq(int irq)
{
	CPU_NVIC_SWTRIG = irq;
}


/* Initialize IRQs in the NVIC and set their priorities as defined by the
 * DECLARE_IRQ statements. */
static void __nvic_init_irqs(void)
{
	/* Get the IRQ priorities section from the linker */
	int exc_calls = __irqprio_end - __irqprio;
	int i;

	/* Mask and clear all pending interrupts */
	for (i = 0; i < 5; i++) {
		CPU_NVIC_DIS(i) = 0xffffffff;
		CPU_NVIC_UNPEND(i) = 0xffffffff;
	}

	/* Re-enable global interrupts in case they're disabled.  On a reboot,
	 * they're already enabled; if we've jumped here from another image,
	 * they're not. */
	interrupt_enable();

	/* Set priorities */
	for (i = 0; i < exc_calls; i++) {
		uint8_t irq = __irqprio[i].irq;
		uint8_t prio = __irqprio[i].priority;
		uint32_t prio_shift = irq % 4 * 8 + 5;
		CPU_NVIC_PRI(irq / 4) =
				(CPU_NVIC_PRI(irq / 4) &
				 ~(0x7 << prio_shift)) |
				(prio << prio_shift);
	}
}


void mutex_lock(struct mutex *mtx)
{
	uint32_t value;
	uint32_t id = 1 << task_get_current();

	ASSERT(id != TASK_ID_INVALID);
	atomic_or(&mtx->waiters, id);

	do {
		/* try to get the lock (set 1 into the lock field) */
		__asm__ __volatile__("   ldrex   %0, [%1]\n"
				     "   teq     %0, #0\n"
				     "   it eq\n"
				     "   strexeq %0, %2, [%1]\n"
				     : "=&r" (value)
				     : "r" (&mtx->lock), "r" (2) : "cc");
		/* "value" is equals to 1 if the store conditional failed,
		 * 2 if somebody else owns the mutex, 0 else.
		 */
		if (value == 2) {
			/* contention on the mutex */
			task_wait_event(0);
		}
	} while (value);

	atomic_clear(&mtx->waiters, id);
}


void mutex_unlock(struct mutex *mtx)
{
	uint32_t waiters;
	task_ *tsk = __get_current();

	__asm__ __volatile__("   ldr     %0, [%2]\n"
			     "   str     %3, [%1]\n"
			     : "=&r" (waiters)
			     : "r" (&mtx->lock), "r" (&mtx->waiters), "r" (0)
			     : "cc");
	while (waiters) {
		task_id_t id = 31 - __builtin_clz(waiters);
		/* somebody is waiting on the mutex */
		task_set_event(id, TASK_EVENT_MUTEX, 0);
		waiters &= ~(1 << id);
	}
	/* Ensure no event is remaining from mutex wake-up */
	atomic_clear(&tsk->events, TASK_EVENT_MUTEX);
}


#ifdef CONFIG_DEBUG


int command_task_info(int argc, char **argv)
{
	int i;

#ifdef CONFIG_TASK_PROFILING
	uart_printf("Task switching started: %10ld us\n", task_start_time);
	uart_printf("Time in tasks:          %10ld us\n",
		    get_time().val - task_start_time);
	uart_printf("Time in exceptions:     %10ld us\n", exc_total_time);
	uart_flush_output();
	uart_printf("Service calls:          %10d\n", svc_calls);
	uart_puts("IRQ counts by type:\n");
	for (i = 0; i < ARRAY_SIZE(irq_dist); i++) {
		if (irq_dist[i])
			uart_printf("%4d %8d\n", i, irq_dist[i]);
	}
#endif

	uart_puts("Task Ready Name         Events    Time (us)\n");

	for (i = 0; i < TASK_ID_COUNT; i++) {
		char is_ready = (tasks_ready & (1<<i)) ? 'R' : ' ';
		uart_printf("%4d %c %-16s %08x %10ld\n", i, is_ready,
			    task_names[i], tasks[i].events, tasks[i].runtime);
		uart_flush_output();
	}


	return EC_SUCCESS;
}
DECLARE_CONSOLE_COMMAND(taskinfo, command_task_info);


static int command_task_ready(int argc, char **argv)
{
	if (argc < 2) {
		uart_printf("tasks_ready: 0x%08x\n", tasks_ready);
	} else {
		tasks_ready = strtoi(argv[1], NULL, 16);
		uart_printf("Setting tasks_ready to 0x%08x\n", tasks_ready);
		__schedule(0, 0);
	}

	return EC_SUCCESS;
}
DECLARE_CONSOLE_COMMAND(taskready, command_task_ready);
#endif


int task_pre_init(void)
{
	/* Fill in guard value in scratchpad to prevent stack overflow
	 * detection failure on the first context switch. */
	((task_ *)scratchpad)->guard = GUARD_VALUE;

	/* sanity checks about static task invariants */
	BUILD_ASSERT(TASK_ID_COUNT <= sizeof(unsigned) * 8);
	BUILD_ASSERT(TASK_ID_COUNT < (1 << (sizeof(task_id_t) * 8)));

	/* Initialize IRQs */
	__nvic_init_irqs();

	return EC_SUCCESS;
}


int task_start(void)
{
#ifdef CONFIG_TASK_PROFILING
	task_start_time = exc_end_time = get_time().val;
#endif

	return __task_start(&need_resched);
}