記事中のプログラムは，Arduino IDE 2.1.1, Board Manager esp32 ver. 2.0.9 で動作確認しています．
信号処理をするにはDSPライブラリがあると大変ありがたい，というか必須かもしれない．ESP32ではどうなっているのか調べると，Espressif DSP Library があり一通りメジャーな処理は用意されている．ただ，Arduino IDE で使えるかどうかが問題．
ESP32のボードマネージャがインストールされたフォルダを調べてみると，かなり深い階層の非常に見つけ難いところに，ヘッダファイル（esp_dsp.h）が置かれていた．どうやらソースコードはないがライブラリも入っている様子．
試しに，IIRフィルタ（2次LPF）を実装してみた．
// I2S on ESP32-S3
// T.Uebo October 1 , 2022
// I2S Master MODE 48kHz/32bit
//
// Mclk GPIO 0
// Bclk GPIO 42
// LRclk GPIO 2
// Dout GPIO 41
// Din GPIO 1
#include <esp_dsp.h>
#include <driver/i2s.h>
#define fsample 48000
#define BLOCK_SAMPLES 64
#define MUTE 40 // MUTE control (LOW: Mute)
//buffers
int rxbuf[BLOCK_SAMPLES*2], txbuf[BLOCK_SAMPLES*2];
float Lch_in[BLOCK_SAMPLES], Rch_in[BLOCK_SAMPLES];
float Lch_out[BLOCK_SAMPLES], Rch_out[BLOCK_SAMPLES];
// for IIR Filter
float zL0[2], zR0[2];
float coeffs[5];
/*-----------------------------------------------------------------------------------------------
Setup
-------------------------------------------------------------------------------------------------*/
void setup(void) {
Serial.begin(115200);
delay(50);
//Mute Control
pinMode(MUTE, OUTPUT);
digitalWrite(MUTE, HIGH); //unmute
pinMode(48, OUTPUT);
// set IIR Filter Coeffs.(as LPF)
dsps_biquad_gen_lpf_f32(coeffs, 0.01f, 1.0f); // fc = 0.01*fsample[Hz], Q=1.0
// I2S setup ------------------------------------------------------------
i2s_config_t i2s_config = {
.mode = (i2s_mode_t)(I2S_MODE_MASTER | I2S_MODE_TX | I2S_MODE_RX),
.sample_rate = fsample,
.bits_per_sample = (i2s_bits_per_sample_t)32,
.channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
.communication_format = (i2s_comm_format_t)(I2S_COMM_FORMAT_STAND_I2S),
.intr_alloc_flags = 0,
.dma_buf_count = 6,
.dma_buf_len = BLOCK_SAMPLES*4,
.use_apll = false,
.tx_desc_auto_clear = true,
.fixed_mclk = 0,
};
i2s_driver_install( I2S_NUM_0, &i2s_config, 0, NULL);
i2s_pin_config_t pin_config = {
.bck_io_num = 42,
.ws_io_num = 2,
.data_out_num = 41,
.data_in_num = 1
};
i2s_set_pin( I2S_NUM_0, &pin_config);
}
/*-----------------------------------------------------------------------------------------------
Signal Process Loop
-------------------------------------------------------------------------------------------------*/
void loop(void) {
size_t readsize = 0;
//Input from I2S codec
esp_err_t rxfb = i2s_read(I2S_NUM_0, &rxbuf[0], BLOCK_SAMPLES*2*4, &readsize, portMAX_DELAY);
if (rxfb == ESP_OK && readsize==BLOCK_SAMPLES*2*4) {
digitalWrite(48, HIGH);
int j=0;
for (int i=0; i<BLOCK_SAMPLES; i++) {
Lch_in[i] = (float) rxbuf[j];
Rch_in[i] = (float) rxbuf[j+1];
j+=2;
}
//-------Signal process -------------------------------
//IIR Filter
dsps_biquad_f32(Lch_in, Lch_out, BLOCK_SAMPLES, coeffs, zL0);
dsps_biquad_f32(Rch_in, Rch_out, BLOCK_SAMPLES, coeffs, zR0);
//------------------------------------------------------
//Output to I2S codec
j=0;
for (int i=0; i<BLOCK_SAMPLES; i++) {
txbuf[j] = (int) Lch_out[i];
txbuf[j+1] = (int) Rch_out[i];
j+=2;
}
i2s_write( I2S_NUM_0, &txbuf[0], BLOCK_SAMPLES*2*4, &readsize, portMAX_DELAY);
}
digitalWrite(48, LOW);
}
I2Sで24bit整数データを取得し，float 32bit で処理しそれを24bit整数にしてI2Sで出力．Octave が便利なので普段はそちらを常用している．
信号処理量の限界を知るために，GPIO48 に信号処理中はHIGHそれ以外はLOWを出力するようにしてその信号を観測してみた．
IIR Biquad フィルタがLch,Rch それぞれ1段なので，処理にかかる時間の割合は非常に小さい．ただHIGHのところが一定でないようなので，拡大すると下のようになっていた．
どうも４ブロック分連続して処理するようになっているらしい．理由はI2Sドライバのソースコードがないのでよくわからない（見てもわからないか…）．そういうものとして理解しておこう．
次に，信号処理を限界まで追加してみる．
// I2S on ESP32-S3
// T.Uebo October 4, 2022
// I2S Master MODE 48kHz/32bit
//
// Mclk GPIO 0
// Bclk GPIO 42
// LRclk GPIO 2
// Dout GPIO 41
// Din GPIO 1
#include <esp_dsp.h>
#include <driver/i2s.h>
#define fsample 48000
#define BLOCK_SAMPLES 64
#define MUTE 40 // MUTE control (LOW: Mute)
//buffers
int rxbuf[BLOCK_SAMPLES*2], txbuf[BLOCK_SAMPLES*2];
float Lch_in[BLOCK_SAMPLES], Rch_in[BLOCK_SAMPLES];
float Lch_out[BLOCK_SAMPLES], Rch_out[BLOCK_SAMPLES];
// for IIR Filter
float zL0[2], zR0[2], coeffs0[5]; // Z^-1配列(Lch)，Z^-1配列 (Rch)，係数
float zL1[2], zR1[2], coeffs1[5];
float zL2[2], zR2[2], coeffs2[5];
float zL3[2], zR3[2], coeffs3[5];
float zL4[2], zR4[2], coeffs4[5];
float zL5[2], zR5[2], coeffs5[5];
float zL6[2], zR6[2], coeffs6[5];
float zL7[2], zR7[2], coeffs7[5];
float zL8[2], zR8[2], coeffs8[5];
float zL9[2], zR9[2], coeffs9[5];
// for FIR filter
#define Nfir 512
fir_f32_t firL_st, firR_st; // FIRではワーク用の構造体を用意する必要がある
float coeffs_firL[Nfir], coeffs_firR[Nfir]; // 係数用配列
float z_firL[Nfir], z_firR[Nfir]; // Z^-1配列
/*-----------------------------------------------------------------------------------------------
Setup
-------------------------------------------------------------------------------------------------*/
void setup(void) {
Serial.begin(115200);
delay(50);
//Mute Control
pinMode(MUTE, OUTPUT);
digitalWrite(MUTE, HIGH); //unmute
pinMode(48, OUTPUT);
// I2S setup ------------------------------------------------------------
i2s_config_t i2s_config = {
.mode = (i2s_mode_t)(I2S_MODE_MASTER | I2S_MODE_TX | I2S_MODE_RX),
.sample_rate = fsample,
.bits_per_sample = (i2s_bits_per_sample_t)32,
.channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
.communication_format = (i2s_comm_format_t)(I2S_COMM_FORMAT_STAND_I2S),
.intr_alloc_flags = 0,
.dma_buf_count = 6,
.dma_buf_len = BLOCK_SAMPLES*4,
.use_apll = false,
.tx_desc_auto_clear = true,
.fixed_mclk = 0,
};
i2s_driver_install( I2S_NUM_0, &i2s_config, 0, NULL);
i2s_pin_config_t pin_config = {
.bck_io_num = 42,
.ws_io_num = 2,
.data_out_num = 41,
.data_in_num = 1
};
i2s_set_pin( I2S_NUM_0, &pin_config);
//-- Filter settings -------------------------------------
// IIR Filter の係数を生成
dsps_biquad_gen_lpf_f32(coeffs0, 0.45f, 1.0f);
dsps_biquad_gen_lpf_f32(coeffs1, 0.45f, 1.0f);
dsps_biquad_gen_lpf_f32(coeffs2, 0.45f, 1.0f);
dsps_biquad_gen_lpf_f32(coeffs3, 0.45f, 1.0f);
dsps_biquad_gen_lpf_f32(coeffs4, 0.45f, 1.0f);
dsps_biquad_gen_lpf_f32(coeffs5, 0.45f, 1.0f);
dsps_biquad_gen_lpf_f32(coeffs6, 0.45f, 1.0f);
dsps_biquad_gen_lpf_f32(coeffs7, 0.45f, 1.0f);
dsps_biquad_gen_lpf_f32(coeffs8, 0.45f, 1.0f);
dsps_biquad_gen_lpf_f32(coeffs9, 0.45f, 1.0f);
// FIR構造体の初期化
dsps_fir_init_f32(&firL_st, coeffs_firL, z_firL, Nfir);
dsps_fir_init_f32(&firR_st, coeffs_firR, z_firR, Nfir);
// FIR Filter の係数を生成.
dsps_d_gen_f32(coeffs_firL, Nfir, 0); // 係数列の先頭を1，その他0
dsps_d_gen_f32(coeffs_firR, Nfir, Nfir-1); // 係数列の最後1，その他0
}
/*-----------------------------------------------------------------------------------------------
Signal Process Loop
-------------------------------------------------------------------------------------------------*/
void loop(void) {
size_t readsize = 0;
//Input from I2S codec
esp_err_t rxfb = i2s_read(I2S_NUM_0, &rxbuf[0], BLOCK_SAMPLES*2*4, &readsize, portMAX_DELAY);
if (rxfb == ESP_OK && readsize==BLOCK_SAMPLES*2*4) {
digitalWrite(48, HIGH);
int j=0;
for (int i=0; i<BLOCK_SAMPLES; i++) {
Lch_in[i] = (float) rxbuf[j];
Rch_in[i] = (float) rxbuf[j+1];
j+=2;
}
//-------Signal process -------------------------------
dsps_biquad_f32(Lch_in, Lch_out, BLOCK_SAMPLES, coeffs0, zL0);
dsps_biquad_f32(Rch_in, Rch_out, BLOCK_SAMPLES, coeffs0, zR0);
dsps_biquad_f32(Lch_out, Lch_in, BLOCK_SAMPLES, coeffs1, zL1);
dsps_biquad_f32(Rch_out, Rch_in, BLOCK_SAMPLES, coeffs1, zR1);
dsps_biquad_f32(Lch_in, Lch_out, BLOCK_SAMPLES, coeffs2, zL2);
dsps_biquad_f32(Rch_in, Rch_out, BLOCK_SAMPLES, coeffs2, zR2);
dsps_biquad_f32(Lch_out, Lch_in, BLOCK_SAMPLES, coeffs3, zL3);
dsps_biquad_f32(Rch_out, Rch_in, BLOCK_SAMPLES, coeffs3, zR3);
dsps_biquad_f32(Lch_in, Lch_out, BLOCK_SAMPLES, coeffs4, zL4);
dsps_biquad_f32(Rch_in, Rch_out, BLOCK_SAMPLES, coeffs4, zR4);
dsps_biquad_f32(Lch_out, Lch_in, BLOCK_SAMPLES, coeffs5, zL5);
dsps_biquad_f32(Rch_out, Rch_in, BLOCK_SAMPLES, coeffs5, zR5);
dsps_biquad_f32(Lch_in, Lch_out, BLOCK_SAMPLES, coeffs6, zL6);
dsps_biquad_f32(Rch_in, Rch_out, BLOCK_SAMPLES, coeffs6, zR6);
dsps_biquad_f32(Lch_out, Lch_in, BLOCK_SAMPLES, coeffs7, zL7);
dsps_biquad_f32(Rch_out, Rch_in, BLOCK_SAMPLES, coeffs7, zR7);
dsps_biquad_f32(Lch_in, Lch_out, BLOCK_SAMPLES, coeffs8, zL8);
dsps_biquad_f32(Rch_in, Rch_out, BLOCK_SAMPLES, coeffs8, zR8);
dsps_biquad_f32(Lch_out, Lch_in, BLOCK_SAMPLES, coeffs9, zL9);
dsps_biquad_f32(Rch_out, Rch_in, BLOCK_SAMPLES, coeffs9, zR9);
dsps_fir_f32(&firL_st, Lch_in, Lch_out, BLOCK_SAMPLES);
dsps_fir_f32(&firR_st, Rch_in, Rch_out, BLOCK_SAMPLES);
//------------------------------------------------------
//Output to I2S codec
j=0;
for (int i=0; i<BLOCK_SAMPLES; i++) {
txbuf[j] = (int) Lch_out[i];
txbuf[j+1] = (int) Rch_out[i];
j+=2;
}
i2s_write( I2S_NUM_0, &txbuf[0], BLOCK_SAMPLES*2*4, &readsize, portMAX_DELAY);
}
digitalWrite(48, LOW);
}
これでGPIO48の信号を見てみると下のようにほぼ限界になっている．
260μsの隙間があるのでもう少し詰められる．試しのFIRのタップ数を増やしていくと580くらいで出力の音がおかしくなった．
ほぼ予想どおり．
Tj Lab 