esp-idf: Unable to set I2S APLL Clock for 48khz 32bit 2ch (IDFGH-432)

I think 176k @ 16bits is the maximum that can be done, taking into account various constraints. The code is the follòwing. The sampling rate required is 2x the original sampling rate and sample size is 32 bits. Then the resulting buffer shall be send to a led connected to the SD line of the I2S, that’s all

 * SPDIF support
 */
#if BYTES_PER_FRAME == 4
typedef ISAMPLE_T s16_t
#else 
typedef ISAMPLE_T s32_t
#endif 
 
#define PREAMBLE_B  (0xE8) //11101000
#define PREAMBLE_M  (0xE2) //11100010
#define PREAMBLE_W  (0xE4) //11100100

#define VUCP   		((0xCC) << 24)
#define VUCP_MUTE 	((0xD4) << 24)	// To mute PCM, set VUCP = invalid.

extern const u16_t spdif_bmclookup[256];

/* 
 SPDIF is supposed to be (before BMC encoding, from LSB to MSB)				
	PPPP AAAA  SSSS SSSS  SSSS SSSS  SSSS VUCP				
 after BMC encoding, each bits becomes 2 hence this becomes a 64 bits word. The
 the trick is to start not with a PPPP sequence but with an VUCP sequence to that
 the 16 bits samples are aligned with a BMC word boundary. Note that the LSB of the
 audio is transmitted first (not the MSB) and that ESP32 libray sends R then L, 
 contrary to what seems to be usually done, so (dst) order had to be changed
*/
void spdif_convert(ISAMPLE_T *src, size_t frames, u32_t *dst, size_t *count) {
	u16_t hi, lo, aux;
	
	// frames are 2 channels of 16 bits
	frames *= 2;

	while (frames--) {
#if BYTES_PER_FRAME == 4		
		hi  = spdif_bmclookup[(u8_t)(*src >> 8)];
		lo  = spdif_bmclookup[(u8_t) *src];
#else
		hi  = spdif_bmclookup[(u8_t)(*src >> 24)];
		lo  = spdif_bmclookup[(u8_t) *src >> 16];
#endif	
		lo ^= ~((s16_t)hi) >> 16;

		// 16 bits sample:
		*(dst+0) = ((u32_t)lo << 16) | hi;

		// 4 bits auxillary-audio-databits, the first used as parity
		aux = 0xb333 ^ (((u32_t)((s16_t)lo)) >> 17);

		// VUCP-Bits: Valid, Subcode, Channelstatus, Parity = 0
		// As parity is always 0, we can use fixed preambles
		if (++(*count) > 383) {
			*(dst+1) =  VUCP | (PREAMBLE_B << 16 ) | aux; //special preamble for one of 192 frames
			*count = 0;
		} else {
			*(dst+1) = VUCP | ((((*count) & 0x01) ? PREAMBLE_W : PREAMBLE_M) << 16) | aux;
		}
		
		src++;
		dst += 2;
	}
}

const u16_t spdif_bmclookup[256] = { //biphase mark encoded values (least significant bit first)
	0xcccc, 0x4ccc, 0x2ccc, 0xaccc, 0x34cc, 0xb4cc, 0xd4cc, 0x54cc,
	0x32cc, 0xb2cc, 0xd2cc, 0x52cc, 0xcacc, 0x4acc, 0x2acc, 0xaacc,
	0x334c, 0xb34c, 0xd34c, 0x534c, 0xcb4c, 0x4b4c, 0x2b4c, 0xab4c,
	0xcd4c, 0x4d4c, 0x2d4c, 0xad4c, 0x354c, 0xb54c, 0xd54c, 0x554c,
	0x332c, 0xb32c, 0xd32c, 0x532c, 0xcb2c, 0x4b2c, 0x2b2c, 0xab2c,
	0xcd2c, 0x4d2c, 0x2d2c, 0xad2c, 0x352c, 0xb52c, 0xd52c, 0x552c,
	0xccac, 0x4cac, 0x2cac, 0xacac, 0x34ac, 0xb4ac, 0xd4ac, 0x54ac,
	0x32ac, 0xb2ac, 0xd2ac, 0x52ac, 0xcaac, 0x4aac, 0x2aac, 0xaaac,
	0x3334, 0xb334, 0xd334, 0x5334, 0xcb34, 0x4b34, 0x2b34, 0xab34,
	0xcd34, 0x4d34, 0x2d34, 0xad34, 0x3534, 0xb534, 0xd534, 0x5534,
	0xccb4, 0x4cb4, 0x2cb4, 0xacb4, 0x34b4, 0xb4b4, 0xd4b4, 0x54b4,
	0x32b4, 0xb2b4, 0xd2b4, 0x52b4, 0xcab4, 0x4ab4, 0x2ab4, 0xaab4,
	0xccd4, 0x4cd4, 0x2cd4, 0xacd4, 0x34d4, 0xb4d4, 0xd4d4, 0x54d4,
	0x32d4, 0xb2d4, 0xd2d4, 0x52d4, 0xcad4, 0x4ad4, 0x2ad4, 0xaad4,
	0x3354, 0xb354, 0xd354, 0x5354, 0xcb54, 0x4b54, 0x2b54, 0xab54,
	0xcd54, 0x4d54, 0x2d54, 0xad54, 0x3554, 0xb554, 0xd554, 0x5554,
	0x3332, 0xb332, 0xd332, 0x5332, 0xcb32, 0x4b32, 0x2b32, 0xab32,
	0xcd32, 0x4d32, 0x2d32, 0xad32, 0x3532, 0xb532, 0xd532, 0x5532,
	0xccb2, 0x4cb2, 0x2cb2, 0xacb2, 0x34b2, 0xb4b2, 0xd4b2, 0x54b2,
	0x32b2, 0xb2b2, 0xd2b2, 0x52b2, 0xcab2, 0x4ab2, 0x2ab2, 0xaab2,
	0xccd2, 0x4cd2, 0x2cd2, 0xacd2, 0x34d2, 0xb4d2, 0xd4d2, 0x54d2,
	0x32d2, 0xb2d2, 0xd2d2, 0x52d2, 0xcad2, 0x4ad2, 0x2ad2, 0xaad2,
	0x3352, 0xb352, 0xd352, 0x5352, 0xcb52, 0x4b52, 0x2b52, 0xab52,
	0xcd52, 0x4d52, 0x2d52, 0xad52, 0x3552, 0xb552, 0xd552, 0x5552,
	0xccca, 0x4cca, 0x2cca, 0xacca, 0x34ca, 0xb4ca, 0xd4ca, 0x54ca,
	0x32ca, 0xb2ca, 0xd2ca, 0x52ca, 0xcaca, 0x4aca, 0x2aca, 0xaaca,
	0x334a, 0xb34a, 0xd34a, 0x534a, 0xcb4a, 0x4b4a, 0x2b4a, 0xab4a,
	0xcd4a, 0x4d4a, 0x2d4a, 0xad4a, 0x354a, 0xb54a, 0xd54a, 0x554a,
	0x332a, 0xb32a, 0xd32a, 0x532a, 0xcb2a, 0x4b2a, 0x2b2a, 0xab2a,
	0xcd2a, 0x4d2a, 0x2d2a, 0xad2a, 0x352a, 0xb52a, 0xd52a, 0x552a,
	0xccaa, 0x4caa, 0x2caa, 0xacaa, 0x34aa, 0xb4aa, 0xd4aa, 0x54aa,
	0x32aa, 0xb2aa, 0xd2aa, 0x52aa, 0xcaaa, 0x4aaa, 0x2aaa, 0xaaaa
};`