Implement clock controller (#93)

Author: moojek

docs/source/pages/api/libs/stdbigos/clock.rst

@@ -0,0 +1,5 @@
+=====
+Clock
+=====
+
+.. doxygengroup:: clock

docs/source/pages/api/libs/stdbigos/index.rst

@@ -10,3 +10,4 @@ Stdbigos
    types
    string
    bitutils
+   clock

include/hal/timer.h

@@ -0,0 +1,52 @@
+#ifndef HAL_TIMER_H
+#define HAL_TIMER_H
+
+#include <stdbigos/error.h>
+#include <stdbigos/types.h>
+
+/**
+ * @addtogroup hal
+ * @{
+ */
+
+/**
+ * @brief Read current monotonic hardware timer value.
+ * @return Current hardware timer tick value.
+ */
+u64 hal_timer_now(void);
+
+/**
+ * @brief Program the next timer interrupt deadline.
+ *
+ * @param deadline Absolute timer value when the interrupt should fire.
+ * @retval ERR_NONE Success
+ * @retval ERR_BAD_ARG Invalid deadline argument
+ * @retval ERR_NOT_IMPLEMENTED Timer SBI extension unsupported
+ * @retval ERR_NOT_VALID Other platform/firmware failure
+ */
+error_t hal_timer_arm_absolute(u64 deadline);
+
+/**
+ * @brief Program next timer interrupt relative to current time.
+ *
+ * @param delta Timer ticks from now
+ * @retval ERR_NONE Success
+ * @retval ERR_BAD_ARG Invalid delta argument
+ * @retval ERR_NOT_IMPLEMENTED Timer SBI extension unsupported
+ * @retval ERR_NOT_VALID Other platform/firmware failure
+ */
+error_t hal_timer_arm_relative(u64 delta);
+
+/**
+ * @brief Enable supervisor timer interrupts.
+ */
+void hal_timer_enable_interrupts(void);
+
+/**
+ * @brief Disable supervisor timer interrupts.
+ */
+void hal_timer_disable_interrupts(void);
+
+/// @}
+
+#endif // !HAL_TIMER_H

include/stdbigos/clock.h

@@ -0,0 +1,91 @@
+#ifndef STDBIGOS_CLOCK
+#define STDBIGOS_CLOCK
+
+#include "error.h"
+#include "types.h"
+
+/**
+ * @file include/stdbigos/clock.h
+ * @brief Public periodic clock API used by the scheduler and examples.
+ *
+ * The periodic clock provides a monotonic time source measured in
+ * architecture-specific ticks and supports scheduling a "next switch"
+ * tick for the scheduler to observe.
+ *
+ * @addtogroup stdbigos
+ * @{
+ * @addtogroup clock
+ * @{
+ */
+
+/**
+ * @brief Initialize the periodic clock subsystem.
+ *
+ * Initialize internal state and program the first timer deadline using
+ * the provided tick quantum.
+ *
+ * @param tick_quantum Number of hardware timer ticks per software tick.
+ * @return error_t E_OK on success, otherwise an error code.
+ */
+error_t clock_init(u64 tick_quantum);
+
+/**
+ * @brief Return the current time in hardware timer ticks.
+ *
+ * This returns a monotonic timestamp suitable for computing deadlines.
+ *
+ * @return Current time in hardware ticks.
+ */
+u64 clock_now(void);
+
+/**
+ * @brief Return the number of software ticks since boot.
+ *
+ * Software ticks are incremented by the timer IRQ handler and advance
+ * at a rate of one per `tick_quantum` hardware ticks.
+ *
+ * @return Number of elapsed software ticks.
+ */
+u64 clock_ticks_now(void);
+
+/**
+ * @brief Request the scheduler be woken in a number of software ticks.
+ *
+ * Programs the next switch tick to be `ticks_from_now` software ticks
+ * in the future. This does not block; use `clock_next_switch_tick`
+ * or `clock_ticks_to_next_switch` to query the scheduled value.
+ *
+ * @param ticks_from_now Number of software ticks from now to schedule.
+ * @return error_t E_OK on success, otherwise an error code.
+ */
+error_t clock_set_next_switch_in(u64 ticks_from_now);
+
+/**
+ * @brief Obtain the currently scheduled next-switch absolute tick.
+ *
+ * Writes the absolute software tick value at which the scheduler has
+ * requested a switch into `out_tick`.
+ *
+ * @param out_tick Pointer to u64 to receive the absolute tick value.
+ * @return error_t E_OK on success, EINVAL if `out_tick` is NULL, or
+ * other error codes on failure.
+ */
+error_t clock_next_switch_tick(u64* out_tick);
+
+/**
+ * @brief Obtain the number of software ticks until the next switch.
+ *
+ * Writes into `out_ticks` the number of ticks remaining until the
+ * scheduled next-switch tick. If a next-switch is not scheduled,
+ * behavior is implementation-defined.
+ *
+ * @param out_ticks Pointer to u64 to receive remaining ticks.
+ * @return error_t E_OK on success, EINVAL if `out_ticks` is NULL, or
+ * other error codes on failure.
+ */
+error_t clock_ticks_to_next_switch(u64* out_ticks);
+
+/** @} */ /* end group clock */
+/** @} */ /* end group stdbigos */
+
+#endif    // !STDBIGOS_CLOCK

include/stdbigos/sbi_utils.h

@@ -0,0 +1,16 @@
+#ifndef _STDBIGOS_SBI_UTILS_H_
+#define _STDBIGOS_SBI_UTILS_H_
+
+#include "error.h"
+#include "sbi.h"
+
+static inline error_t sbi_map_error(sbi_error_t err) {
+	switch (err) {
+	case SBI_SUCCESS:           return ERR_NONE;
+	case SBI_ERR_INVALID_PARAM: return ERR_BAD_ARG;
+	case SBI_ERR_NOT_SUPPORTED: return ERR_NOT_IMPLEMENTED;
+	default:                    return ERR_NOT_VALID;
+	}
+}
+
+#endif // !_STDBIGOS_SBI_UTILS_H_

src/example_sbi/CMakeLists.txt

@@ -1,5 +1,5 @@
 SETUP_EXECUTABLE(example_sbi)
 
-target_link_libraries(example_sbi PRIVATE startup stdbigos)
+target_link_libraries(example_sbi PRIVATE startup stdbigos hal)
 
 ADD_QEMU_TARGET(example_sbi)

src/example_sbi/entry.c

@@ -1,3 +1,6 @@
+#include <hal/timer.h>
+#include <hal/trap.h>
+#include <stdbigos/clock.h>
 #include <stdbigos/sbi.h>
 #include <stdbigos/types.h>
 
@@ -6,5 +9,31 @@ static void sbi_puts(const char* str) {
 }
 
 void main([[maybe_unused]] u32 hartid, [[maybe_unused]] const void* fdt) {
-	sbi_puts("Hello world\n");
+	if (hal_trap_init() != ERR_NONE) {
+		sbi_puts("trap init failed\n");
+		return;
+	}
+
+	error_t err = clock_init(50000llu);
+	if (err != ERR_NONE) {
+		sbi_puts("clock init failed\n");
+		return;
+	}
+
+	hal_timer_enable_interrupts();
+
+	sbi_puts("clock started\n");
+
+	u64 last_tick = clock_ticks_now();
+	while (true) {
+		hal_wait_for_interrupt();
+
+		u64 now_tick = clock_ticks_now();
+		if (now_tick != last_tick) {
+			if ((now_tick % 100) == 0) {
+				sbi_puts("tick periodic\n");
+			}
+			last_tick = now_tick;
+		}
+	}
 }

src/lib/hal/arch/riscv/timer.c

@@ -0,0 +1,41 @@
+#include <hal/timer.h>
+#include <stdbigos/sbi.h>
+#include <stdbigos/sbi_utils.h>
+
+#include "csr.h"
+#include "trap.h"
+
+u64 hal_timer_now(void) {
+	u64 now;
+	__asm__ volatile("rdtime %0" : "=r"(now)::"memory");
+	return now;
+}
+
+error_t hal_timer_arm_absolute(u64 deadline) {
+	if (deadline == 0) {
+		return ERR_BAD_ARG;
+	}
+
+	struct sbiret ret = sbi_set_timer(deadline);
+	if (ret.error == SBI_ERR_NOT_SUPPORTED) {
+		ret = sbi_legacy_set_timer(deadline);
+	}
+
+	return sbi_map_error(ret.error);
+}
+
+error_t hal_timer_arm_relative(u64 delta) {
+	if (delta == 0) {
+		return ERR_BAD_ARG;
+	}
+
+	return hal_timer_arm_absolute(hal_timer_now() + delta);
+}
+
+void hal_timer_enable_interrupts(void) {
+	CSR_SET(sie, 1ul << HAL_RISCV_TRAP_INT_S_TIMER);
+}
+
+void hal_timer_disable_interrupts(void) {
+	CSR_CLEAR(sie, 1ul << HAL_RISCV_TRAP_INT_S_TIMER);
+}

src/lib/stdbigos/clock.c

@@ -0,0 +1,107 @@
+#include <hal/timer.h>
+#include <hal/trap.h>
+#include <stdbigos/clock.h>
+
+static u64 g_tick_quantum;
+static u64 g_next_deadline;
+static u64 g_ticks;
+static u64 g_next_switch_tick;
+
+static error_t clock_program_timer(u64 deadline) {
+	error_t err = hal_timer_arm_absolute(deadline);
+	if (err != ERR_NONE) {
+		return err;
+	}
+
+	return ERR_NONE;
+}
+
+static error_t clock_schedule_next_deadline(void) {
+	if (g_tick_quantum == 0) {
+		return ERR_NOT_INITIALIZED;
+	}
+
+	g_next_deadline = clock_now() + g_tick_quantum;
+	return clock_program_timer(g_next_deadline);
+}
+
+static void clock_timer_irq_handler(void) {
+	++g_ticks;
+	(void)clock_schedule_next_deadline();
+}
+
+u64 clock_now(void) {
+	return hal_timer_now();
+}
+
+u64 clock_ticks_now(void) {
+	return g_ticks;
+}
+
+error_t clock_init(u64 tick_quantum) {
+	if (tick_quantum == 0) {
+		return ERR_BAD_ARG;
+	}
+
+	error_t err = hal_trap_register_timer_handler(clock_timer_irq_handler);
+	if (err != ERR_NONE) {
+		return err;
+	}
+
+	g_ticks = 0;
+	g_tick_quantum = tick_quantum;
+	g_next_switch_tick = 0;
+	return clock_schedule_next_deadline();
+}
+
+error_t clock_set_next_switch_in(u64 ticks_from_now) {
+	if (g_tick_quantum == 0) {
+		return ERR_NOT_INITIALIZED;
+	}
+
+	if (ticks_from_now == 0) {
+		return ERR_BAD_ARG;
+	}
+
+	g_next_switch_tick = g_ticks + ticks_from_now;
+	return ERR_NONE;
+}
+
+error_t clock_next_switch_tick(u64* out_tick) {
+	if (out_tick == NULL) {
+		return ERR_BAD_ARG;
+	}
+
+	if (g_tick_quantum == 0) {
+		return ERR_NOT_INITIALIZED;
+	}
+
+	if (g_next_switch_tick == 0) {
+		return ERR_NOT_FOUND;
+	}
+
+	*out_tick = g_next_switch_tick;
+	return ERR_NONE;
+}
+
+error_t clock_ticks_to_next_switch(u64* out_ticks) {
+	if (out_ticks == NULL) {
+		return ERR_BAD_ARG;
+	}
+
+	if (g_tick_quantum == 0) {
+		return ERR_NOT_INITIALIZED;
+	}
+
+	if (g_next_switch_tick == 0) {
+		return ERR_NOT_FOUND;
+	}
+
+	if (g_ticks >= g_next_switch_tick) {
+		*out_ticks = 0;
+		return ERR_NONE;
+	}
+
+	*out_ticks = g_next_switch_tick - g_ticks;
+	return ERR_NONE;
+}