Peripherals

1. Introduction

The Nintendo DS and DSi has several peripherals that you’re unlikely to use in most applications, but can be very useful in some specific applications.

2. Battery

You can check the status of the battery easily, but the information you can obtain depends on the DS model:

• Original DS: You can only check if the battery level is high or low.
• DS Lite: You can also check if the charger is connected or not. Some of them support reading 15 charge levels.
• DSi: You can check if the charger is connected or not, and 15 different charge levels.

Libnds abstracts the different consoles and it provides one single function to check this information from both the ARM9 and ARM7:

u32 value = getBatteryLevel();
unsigned int battery_level = value & BATTERY_LEVEL_MASK;
bool charger_connected = value & BATTERY_CHARGER_CONNECTED;

printf("Current charge level: %u\n", battery_level);
printf("Charger connected: %s\n", charger_connected ? "Yes" : "No");

You can check this code in action in this example: examples/peripherals/battery_status

3. Hardware divider and square root

The ARM9 has access to some registers that can calculate integer divisions and square roots by hardware. This can help you optimize applications because the CPUs of the DS don’t support division or square root and they need to be calculated by software. The registers work asynchronously, so you can even let the hardware calculate something while you do other things:

div32_asynch(7000, 3); // Start division
u32 sqrt_out = sqrt64(12345 * 12345);
u32 div_out = div32_result(); // Read division result

You can check all helpers provided by libnds in the documentation here. There are some helpers to do regular integer division and square root, as well as some helpers to do fixed point divisions and square roots.

You can check this code in action in this example: examples/peripherals/maths_coprocessor

4. Real Time Clock

You can get the current time by using the standard C function time(). You can use its returned value the same way you’d use it in any C program. For example:

#include <time.h>

// ...

char str[100];

time_t t = time(NULL);
struct tm *tmp = localtime(&t);

if (strftime(str, sizeof(str), "%Y-%m-%dT%H:%M:%S%z", tmp) == 0)
    snprintf(str, sizeof(str), "Failed to get time");

printf("%s", str);

You can also set the date and time in the RTC chip. This must be done from the ARM7, libnds doesn’t provide any helper to do it from the ARM9 at the moment. You can set the time and date simultaneously or just the time:

rtcTimeAndDate rtc_time_date = { ... };

if (rtcTimeAndDateSet(&rtc_time_date) != 0)
{
    // Error
}

rtcTime rtc_time = { ... };

if (rtcTimeet(&rtc_time) != 0)
{
    // Error
}

Remember to subtract 2000 from the real year when writing the values of a rtcTimeAndDate struct!

You can check this code in action in this example: examples/time/rtc_set_get