PROGMEM for IR command storage

Question

I'm working on a code that is able to send raw data as IR signal to IR transmitter, the memory of arduino Nano is not enough to store the array in SRAM storage,so i'm about to use PROGMEM to store arrays in flash memory.

these are arrays for IR signal raw command:

unsigned int irSignaloff[]={6060, 7420, 532, 1652, 544, 1668, 508, 1688, 508, 1688, 508, 1692, 532, 1664, 532, 1664, 532, 1664, 536, 604, 528, 588, 548, 580, 552, 580, 528, 636, 500, 600, 532, 588, 548, 580, 552, 1644, 552, 1644, 528, 1664, 532, 1668, 532, 1664, 532, 1668, 528, 1668, 528, 1668, 508, 624, 536, 600, 532, 600, 536, 576, 528, 600, 532, 604, 532, 604, 532, 580, 552, 1648, 548, 1648, 552, 1644, 552, 1648, 552, 1644, 552, 1640, 556, 1644, 528, 1668, 528, 600, 508, 624, 512, 620, 536, 600, 536, 604, 528, 576, 508, 624, 532, 604, 532, 1660, 536, 1660, 540, 596, 536, 1644, 552, 1648, 552, 1644, 552, 580, 524, 1672, 524, 604, 508, 624, 536, 1660, 536, 632, 504, 580, 552, 608, 500, 1668, 528, 600, 508, 1688, 512, 1684, 560, 1668, 504, 660, 500, 1660, 536, 604, 532, 1656, 540, 1660, 540, 584, 548, 580, 528, 596, 512, 1688, 508, 660, 500, 1660, 536, 596, 540, 584, 548, 604, 500, 1672, 528, 600, 512, 1684, 512, 620, 540, 1656, 540, 600, 536, 580, 552, 1644, 552, 576, 528, 1668, 532, 600, 508, 1688, 536, 596, 536, 1660, 540, 1660, 536, 7420, 536};



unsigned int irSignalon[]={6156, 7336, 592, 1588, 612, 1584, 612, 1588, 608, 1588, 608, 1588, 604, 1592, 604, 1592, 604, 1592, 604, 528, 504, 628, 588, 548, 588, 552, 580, 524, 608, 524, 572, 560, 592, 540, 588, 1608, 592, 1604, 592, 1604, 592, 1608, 592, 1604, 592, 1604, 592, 1604, 596, 1600, 596, 524, 608, 520, 584, 544, 596, 540, 596, 536, 596, 524, 608, 520, 604, 524, 588, 1608, 588, 1608, 588, 1608, 588, 1608, 588, 1612, 536, 1660, 572, 1624, 572, 1628, 564, 600, 504, 628, 504, 580, 528, 600, 636, 528, 540, 564, 532, 588, 548, 604, 504, 1664, 532, 604, 504, 624, 536, 1660, 532, 1664, 532, 1664, 532, 604, 532, 1660, 536, 584, 548, 1652, 548, 1644, 552, 580, 556, 572, 532, 604, 532, 1664, 532, 600, 532, 1668, 532, 1660, 536, 1688, 532, 600, 536, 1664, 532, 584, 620, 1576, 552, 1644, 552, 576, 532, 604, 608, 524, 532, 1664, 608, 512, 620, 1576, 548, 580, 556, 572, 600, 536, 604, 1588, 608, 528, 536, 1660, 536, 584, 620, 1580, 620, 508, 596, 532, 508, 1688, 512, 620, 536, 1660, 604, 532, 608, 1588, 604, 516, 620, 1576, 620, 1576, 624, 7308, 552}; 

and this is sending command uses IRemote.h library:

 irSend.sendRaw(irSignalon, sizeon, FREQ_KHZ, false);

so how can i use PROGMEM to store and read this int array in order to send them? thanks

Answer 1

If your IR library does not support sending signals stored in PROGMEM, then you will have to provide the data in RAM. However, you do not have to keep both signals in RAM permanently: only the one you are about to send needs to be there.

I suggest you keep all the IR signal data in PROGMEM while not sending them. Whenever you want to send a signal, you copy it to a RAM-based buffer and give the address of that buffer to the library. The same buffer will be reused for any signal you are sending. This will cost you some CPU time for the copy, and save 394 bytes of RAM. The savings will scale up if you add more signals to your sketch.

const size_t signal_size = 197;

static PROGMEM const uint16_t irSignaloff[signal_size] = { ... };

static PROGMEM const uint16_t irSignalon[signal_size] = { ... };

/* Send an IR signal from PROGMEM. */
void send_signal(const uint16_t *signal) {
    static uint16_t signal_buffer[signal_size];
    memcpy_P(signal_buffer, signal, signal_size * sizeof *signal);
    irSend.sendRaw(signal_buffer, signal_size, FREQ_KHZ, false);
}

//...
send_signal(irSignalon);
send_signal(irSignaloff);

Here I am assuming that all your signals have the same length, which is true for the example you show, but may be false if you add more signals later. You may then need to size the buffer as the longest of all your signals, and provide the signal length as an extra parameter to send_signal().

Note that the RAM buffer does not need to be static. I chose to make it static here only in order for avr-size to give you a good estimate of the memory requirement of the program.