Get ACPI battery BST data in FreeBSD

get_bst.c

#include <err.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/ioctl.h>
#include <sysexits.h>
#include <unistd.h>

#include <dev/acpica/acpiio.h>

#include <contrib/dev/acpica/include/acpi.h>

#define ACPIDEV		"/dev/acpi"
#define UNKNOWN_VOLTAGE 0xffffffff

//struct acpi_bst {
//	uint32_t state;			/* Battery State */
//	uint32_t rate;			/* Present Rate */
//	uint32_t cap;			/* Remaining Capacity */
//	uint32_t volt;			/* Present Voltage */
//};

//union acpi_battery_ioctl_arg {
//	int			 unit;	/* Device unit or ACPI_BATTERY_ALL_UNITS. */
//	struct acpi_battinfo battinfo;
//	struct acpi_bif	 bif;
//	struct acpi_bst	 bst;
//};

static int	acpifd;

static void acpi_init(void) {
	printf("DEBUG: begin acpi_init\n");
	printf("DEBUG: Opening /dev/acpi\n");
	acpifd = open(ACPIDEV, O_RDONLY);
	if (acpifd == -1) {
		printf("ERROR: Failed to open /dev/acpi\n");
		err(EX_OSFILE, ACPIDEV);
	} else {
		printf("DEBUG: Success!\n");
	}
	printf("DEBUG: end acpi_init\n");
}

static int acpi_battinfo(int num) {
	printf("DEBUG: begin acpi_battinfo\n");
	union acpi_battery_ioctl_arg battio;
	const char *pwr_units;
	int hours, min, amp;
	uint32_t volt;

	if (num < 0 || num > 64)
		errx(EX_USAGE, "invalid battery %d", num);

	/* Fetch BST information. */
	volt = UNKNOWN_VOLTAGE;		// 0xffffffff
	battio.unit = num;
	if (ioctl(acpifd, ACPIIO_BATT_GET_BST, &battio) == -1) {
		printf("get battery status (%d) failed\n", num);
		err(EX_IOERR, "get battery status (%d) failed", num);
	}
	if (battio.bst.state != ACPI_BATT_STAT_NOT_PRESENT) {
		printf("DEBUG: we can use BST for voltage!\n");
		volt = battio.bst.volt;
	}

	/* Print BST information */
	printf("BST_STATE: charging/discharging and critical low\n");
	printf("BST_RATE:  power/current supplied or accepted through terminals\n");
	printf("BST_CAP:   estimated remaining capacity\n");
	printf("BST_VOLT:  voltage across terminals\n");
	printf("BST_STATE: %10u : %-#10x\n", battio.bst.state, battio.bst.state);
	printf("BST_RATE:  %10u : %-#10x\n", battio.bst.rate, battio.bst.rate);
	printf("BST_CAP:   %10u : %-#10x\n", battio.bst.cap, battio.bst.cap);
	printf("BST_VOLT:  %10u : %-#10x\n", battio.bst.volt, battio.bst.volt);
	printf("DEBUG: end acpi_battinfo\n");
	return (0);
}

int main(int argc, char *argv[]) {
	printf("DEBUG: begin main\n");
	int	battery = 0;
	acpi_init();
	acpi_battinfo(battery);
	close(acpifd);
	printf("DEBUG: end main\n");
	exit (0);
}

out

$ cc -o get_bst -I/usr/src/sys get_bst.c && ./get_bst
DEBUG: begin main
DEBUG: begin acpi_init
DEBUG: Opening /dev/acpi
DEBUG: Success!
DEBUG: end acpi_init
DEBUG: begin acpi_battinfo
DEBUG: we can use BST for voltage!
BST_STATE: charging/discharging and critical low
BST_RATE:  power/current supplied or accepted through terminals
BST_CAP:   estimated remaining capacity
BST_VOLT:  voltage across terminals
BST_STATE:          1 : 0x1       
BST_RATE:       15983 : 0x3e6f    
BST_CAP:        16970 : 0x424a    
BST_VOLT:  4294967295 : 0xffffffff
DEBUG: end acpi_battinfo
DEBUG: end main