tests/kernel/fp_sharing/src/main.c

/* main.c - load/store portion of FPU sharing test */

/*
 * Copyright (c) 2011-2014 Wind River Systems, Inc.
 *
 * SPDX-License-Identifier: Apache-2.0
 */

/*
 * DESCRIPTION
 * This module implements the load/store portion of the FPU sharing test. This
 * version of this test utilizes a pair of tasks.
 *
 * The load/store test validates the floating point unit context
 * save/restore mechanism. This test utilizes a pair of threads of different
 * priorities that each use the floating point registers. The context
 * switching that occurs exercises the kernel's ability to properly preserve the
 * floating point registers. The test also exercises the kernel's ability to
 * automatically enable floating point support for a task, if supported.
 *
 * FUTURE IMPROVEMENTS
 * On architectures where the non-integer capabilities are provided in a
 *  hierarchy, for example on IA-32 the USE_FP and USE_SSE options are provided,
 * this test should be enhanced to ensure that the architectures' _Swap()
 * routine doesn't context switch more registers that it needs to (which would
 * represent a performance issue).  For example, on the IA-32, the test should
 * issue a fiber_fp_disable() from main(), and then indicate that only x87 FPU
 * registers will be utilized (fiber_fp_enable()).  The fiber should continue
 * to load ALL non-integer registers, but main() should validate that only the
 * x87 FPU registers are being saved/restored.
 */

#ifndef CONFIG_FLOAT
#error Rebuild with the FLOAT config option enabled
#endif

#ifndef CONFIG_FP_SHARING
#error Rebuild with the FP_SHARING config option enabled
#endif

#if defined(CONFIG_ISA_IA32)
#ifndef CONFIG_SSE
#error Rebuild with the SSE config option enabled
#endif
#endif /* CONFIG_ISA_IA32 */

#include <zephyr.h>

#if defined(CONFIG_ISA_IA32)
  #if defined(__GNUC__)
    #include <float_regs_x86_gcc.h>
  #else
    #include <float_regs_x86_other.h>
  #endif /* __GNUC__ */
#elif defined(CONFIG_CPU_CORTEX_M4)
  #if defined(__GNUC__)
    #include <float_regs_arm_gcc.h>
  #else
    #include <float_regs_arm_other.h>
  #endif /* __GNUC__ */
#endif

#include <arch/cpu.h>
#include <tc_util.h>
#include "float_context.h"
#include <stddef.h>
#include <string.h>

#define MAX_TESTS 500
#define STACKSIZE 2048
#define HI_PRI	5
#define LO_PRI	10

/* space for float register load/store area used by low priority task */

static struct fp_register_set float_reg_set_load;
static struct fp_register_set float_reg_set_store;

/* space for float register load/store area used by high priority thread */

static struct fp_register_set float_reg_set;


/* flag indicating that an error has occurred */

int fpu_sharing_error;

/*
 * Test counters are "volatile" because GCC may not update them properly
 * otherwise. (See description of pi calculation test for more details.)
 */

static volatile unsigned int load_store_low_count;
static volatile unsigned int load_store_high_count;

extern uint32_t _tick_get_32(void);
extern void calculate_pi_low(void);
extern void calculate_pi_high(void);

/**
 *
 * @brief Low priority FPU load/store thread
 *
 * @return N/A
 */

void load_store_low(void)
{
	unsigned int i;
	unsigned char init_byte;
	unsigned char *store_ptr = (unsigned char *)&float_reg_set_store;
	unsigned char *load_ptr = (unsigned char *)&float_reg_set_load;

	volatile char volatile_stack_var = 0;

	PRINT_DATA("Floating point sharing tests started\n");
	PRINT_LINE;

	/*
	 * The high priority thread has a sleep to get this (low pri) thread
	 * running and here (low priority) we enable slicing and waste cycles
	 * to run hi pri thread in between fp ops.
	 *
	 * Enable round robin scheduling to allow both the low priority pi
	 * computation and load/store tasks to execute. The high priority pi
	 * computation and load/store tasks will preempt the low priority tasks
	 * periodically.
	 */

	k_sched_time_slice_set(10, LO_PRI);

	/*
	 * Initialize floating point load buffer to known values;
	 * these values must be different than the value used in other threads.
	 */

	init_byte = MAIN_FLOAT_REG_CHECK_BYTE;
	for (i = 0; i < SIZEOF_FP_REGISTER_SET; i++) {
		load_ptr[i] = init_byte++;
	}

	/* Keep cranking forever, or until an error is detected. */

	for (load_store_low_count = 0; ; load_store_low_count++) {

		/*
		 * Clear store buffer to erase all traces of any previous
		 * floating point values that have been saved.
		 */

		memset(&float_reg_set_store, 0, SIZEOF_FP_REGISTER_SET);

		/*
		 * Utilize an architecture specific function to load all the
		 * floating point registers with known values.
		 */

		_load_all_float_registers(&float_reg_set_load);

		/*
		 * Waste some cycles to give the high priority load/store
		 * thread an opportunity to run when the low priority thread is
		 * using the floating point registers.
		 *
		 * IMPORTANT: This logic requires that sys_tick_get_32() not
		 * perform any floating point operations!
		 */

		while ((_tick_get_32() % 5) != 0) {
			/*
			 * Use a volatile variable to prevent compiler
			 * optimizing out the spin loop.
			 */
			++volatile_stack_var;
		}

		/*
		 * Utilize an architecture specific function to dump the
		 * contents of all floating point registers to memory.
		 */

		_store_all_float_registers(&float_reg_set_store);

		/*
		 * Compare each byte of buffer to ensure the expected value is
		 * present, indicating that the floating point registers weren't
		 * impacted by the operation of the high priority thread(s).
		 *
		 * Display error message and terminate if discrepancies are
		 * detected.
		 */

		init_byte = MAIN_FLOAT_REG_CHECK_BYTE;

		for (i = 0; i < SIZEOF_FP_REGISTER_SET; i++) {
			if (store_ptr[i] != init_byte) {
				TC_ERROR("load_store_low found 0x%x instead "
					"of 0x%x @ offset 0x%x\n",
						store_ptr[i],
						init_byte, i);
				TC_ERROR("Discrepancy found during "
						"iteration %d\n",
						load_store_low_count);
				fpu_sharing_error = 1;
			}
			init_byte++;
		}

		/*
		 * Terminate if a test error has been reported.
		 */

		if (fpu_sharing_error) {
			TC_END_RESULT(TC_FAIL);
			TC_END_REPORT(TC_FAIL);
			return;
		}

#if defined(CONFIG_ISA_IA32)
		/*
		 * After every 1000 iterations (arbitrarily chosen), explicitly
		 * disable floating point operations for the task. The
		 * subsequent execution of _load_all_float_registers() will
		 * result in an exception to automatically re-enable
		 * floating point support for the task.
		 *
		 * The purpose of this part of the test is to exercise the
		 * k_float_disable() API, and to also continue exercising
		 * the (exception based) floating enabling mechanism.
		 */
		if ((load_store_low_count % 1000) == 0) {
			k_float_disable(k_current_get());
		}
#elif defined(CONFIG_CPU_CORTEX_M4)
		/*
		 * The routine k_float_disable() allows for thread-level
		 * granularity for disabling floating point. Furthermore, it
		 * is useful for testing on the fly thread enabling of floating
		 * point. Neither of these capabilities are currently supported
		 * for ARM.
		 */
#endif
	}
}

/**
 *
 * @brief High priority FPU load/store thread
 *
 * @return N/A
 */

void load_store_high(void)
{
	unsigned int i;
	unsigned char init_byte;
	unsigned char *reg_set_ptr = (unsigned char *)&float_reg_set;

	/* test until the specified time limit, or until an error is detected */

	while (1) {
		/*
		 * Initialize the float_reg_set structure by treating it as
		 * a simple array of bytes (the arrangement and actual number
		 * of registers is not important for this generic C code).  The
		 * structure is initialized by using the byte value specified
		 * by the constant FIBER_FLOAT_REG_CHECK_BYTE, and then
		 * incrementing the value for each successive location in the
		 * float_reg_set structure.
		 *
		 * The initial byte value, and thus the contents of the entire
		 * float_reg_set structure, must be different for each
		 * thread to effectively test the nanokernel's ability to
		 * properly save/restore the floating point values during a
		 * context switch.
		 */

		init_byte = FIBER_FLOAT_REG_CHECK_BYTE;

		for (i = 0; i < SIZEOF_FP_REGISTER_SET; i++) {
			reg_set_ptr[i] = init_byte++;
		}

		/*
		 * Utilize an architecture specific function to load all the
		 * floating point registers with the contents of the
		 * float_reg_set structure.
		 *
		 * The goal of the loading all floating point registers with
		 * values that differ from the values used in other threads is
		 * to help determine whether the floating point register
		 * save/restore mechanism in the nanokernel's context switcher
		 * is operating correctly.
		 *
		 * When a subsequent nano_fiber_timer_test() invocation is
		 * performed, a (cooperative) context switch back to the
		 * preempted task will occur. This context switch should result
		 * in restoring the state of the task's floating point
		 * registers when the task was swapped out due to the
		 * occurrence of the timer tick.
		 */

		_load_then_store_all_float_registers(&float_reg_set);

		/*
		 * Relinquish the processor for the remainder of the current
		 * system clock tick, so that lower priority threads get a
		 * chance to run.
		 *
		 * This exercises the ability of the nanokernel to restore the
		 * FPU state of a low priority thread _and_ the ability of the
		 * nanokernel to provide a "clean" FPU state to this thread
		 * once the sleep ends.
		 */

		k_sleep(1);

		/* periodically issue progress report */

		if ((++load_store_high_count % 100) == 0) {
			PRINT_DATA("Load and store OK after %u (high) "
					"+ %u (low) tests\n",
					load_store_high_count,
					load_store_low_count);
		}

		/* terminate testing if specified limit has been reached */

		if (load_store_high_count == MAX_TESTS) {
			TC_END_RESULT(TC_PASS);
			TC_END_REPORT(TC_PASS);
			return;
		}
	}
}

#if defined(CONFIG_ISA_IA32)
#define THREAD_FP_FLAGS	(K_FP_REGS | K_SSE_REGS)
#else
#define THREAD_FP_FLAGS	(K_FP_REGS)
#endif

K_THREAD_DEFINE(load_low, STACKSIZE, load_store_low, NULL, NULL, NULL,
			LO_PRI, THREAD_FP_FLAGS, K_NO_WAIT);

K_THREAD_DEFINE(load_high, STACKSIZE, load_store_high, NULL, NULL, NULL,
			HI_PRI, THREAD_FP_FLAGS, K_NO_WAIT);

K_THREAD_DEFINE(pi_low, STACKSIZE, calculate_pi_low, NULL, NULL, NULL,
			LO_PRI, THREAD_FP_FLAGS, K_NO_WAIT);

K_THREAD_DEFINE(pi_high, STACKSIZE, calculate_pi_high, NULL, NULL, NULL,
			HI_PRI, THREAD_FP_FLAGS, K_NO_WAIT);