kopia lustrzana https://github.com/bitluni/ESP32AMRadioTransmitter
72 wiersze
2.9 KiB
C++
72 wiersze
2.9 KiB
C++
//code by bitluni (send me a high five if you like the code)
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//replace this include file by your header file generated by the conversion tool
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#include "sample.h"
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#include <soc/rtc.h>
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#include "driver/i2s.h"
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static const i2s_port_t i2s_num = (i2s_port_t)I2S_NUM_0; // i2s port number
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//static i2s_config_t i2s_config;
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static const i2s_config_t i2s_config = {
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.mode = (i2s_mode_t)(I2S_MODE_MASTER | I2S_MODE_TX | I2S_MODE_DAC_BUILT_IN),
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.sample_rate = 1000000, //not really used
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.bits_per_sample = (i2s_bits_per_sample_t)I2S_BITS_PER_SAMPLE_16BIT,
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.channel_format = I2S_CHANNEL_FMT_ONLY_RIGHT,
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.communication_format = I2S_COMM_FORMAT_STAND_MSB,
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.intr_alloc_flags = ESP_INTR_FLAG_LEVEL1,
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.dma_buf_count = 2,
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.dma_buf_len = 1024 //big buffers to avoid noises
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};
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void setup()
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{
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Serial.begin(115200);
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setCpuFrequencyMhz(240); //highest cpu frequency
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i2s_driver_install(i2s_num, &i2s_config, 0, NULL); //start i2s driver
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i2s_set_pin(i2s_num, NULL); //use internal DAC
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i2s_set_sample_rates(i2s_num, 1000000); //dummy sample rate, since the function fails at high values
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//this is the hack that enables the highest sampling rate possible ~13MHz, have fun
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SET_PERI_REG_BITS(I2S_CLKM_CONF_REG(0), I2S_CLKM_DIV_A_V, 1, I2S_CLKM_DIV_A_S);
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SET_PERI_REG_BITS(I2S_CLKM_CONF_REG(0), I2S_CLKM_DIV_B_V, 1, I2S_CLKM_DIV_B_S);
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SET_PERI_REG_BITS(I2S_CLKM_CONF_REG(0), I2S_CLKM_DIV_NUM_V, 2, I2S_CLKM_DIV_NUM_S);
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SET_PERI_REG_BITS(I2S_SAMPLE_RATE_CONF_REG(0), I2S_TX_BCK_DIV_NUM_V, 2, I2S_TX_BCK_DIV_NUM_S);
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}
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//buffer to store modulated samples, I2S samples of the esp32 are always 16Bit
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short buff[1024];
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//sine represented in 16 values. at 13MHz sampling rate the resulting carrier is at around 835KHz
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int sintab[] = {0, 48, 90, 117, 127, 117, 90, 48, 0, -48, -90, -117, -127, -117, -90, -48};
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unsigned long long pos = 0; //current position in the audio sample, using fixed point
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unsigned int posLow = 0;
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unsigned long long posInc = ((unsigned long long)sampleRate << 32) / 835000; //sample fixed increment
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void loop()
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{
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//fill the sound buffer
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for(int i = 0; i < 1024; i+=16)
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{
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if(posLow >= sampleCount) posLow = sampleCount - 1;
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//taking current sample
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int s = samples[posLow] + 128;
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//modulating that sample on the 16 values of the carrier wave (respect to I2S byte order, 16Bit/Sample)
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for(int j = 0; j < 16; j += 4)
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{
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buff[i + j + 1] = (sintab[j + 0] * s + 0x8000);
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buff[i + j + 0] = (sintab[j + 1] * s + 0x8000);
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buff[i + j + 3] = (sintab[j + 2] * s + 0x8000);
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buff[i + j + 2] = (sintab[j + 3] * s + 0x8000);
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}
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pos += posInc;
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posLow = pos >> 32;
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if(posLow >= sampleCount)
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pos = posLow = 0;
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}
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//write the buffer (waits until a buffer is ready to be filled, that's timing for free)
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size_t bytes_written;
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i2s_write(i2s_num, (char*)buff, sizeof(buff), &bytes_written, portMAX_DELAY);
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}
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