Slow MJPEG stream with LwIP, ERR_MEM when sending large data

[Dangcaominh]

Hello!
I am using STM32F427VIT6 and OV5640 camera to stream MJPEG to a webserver. I used DCMI DMA to get a jpeg_frame, size around 10KB to 25KB per image, with almost 30FPS and send it to jpeg buffer in CCMRAM like this.

__attribute__((section(".ccmram"))) __attribute__((aligned(32))) uint8_t jpeg[32768];
__attribute__((section(".ccmram"))) __attribute__((aligned(32))) uint32_t jpegLength = 0;

 Then I used LwIP with raw TCP, tcp_write() function to send it to webserver but it's very laggy, sometimes return ERR_MEM in this function

LWIP_DEBUGF(TCP_OUTPUT_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("tcp_write : could not allocate memory for pbuf copy size %"U16_F"\n", seglen));
        goto memerr;

Although I spent nearly 100% of my RAM allocating for LwIP heap memory and SND buffer. Here is my LwIP mem config

/*----- Default Value for MEMP_NUM_TCP_PCB: 5 ---*/
#define MEMP_NUM_TCP_PCB 1
/*----- Value in opt.h for NO_SYS: 0 -----*/
#define NO_SYS 1
/*----- Value in opt.h for SYS_LIGHTWEIGHT_PROT: 1 -----*/
#define SYS_LIGHTWEIGHT_PROT 0
/*----- Value in opt.h for MEM_ALIGNMENT: 1 -----*/
#define MEM_ALIGNMENT 4
/*----- Default Value for MEM_SIZE: 1600 ---*/
#define MEM_SIZE 32768
/*----- Default Value for MEMP_NUM_TCP_SEG: 16 ---*/
#define MEMP_NUM_TCP_SEG 2048
/*----- Default Value for PBUF_POOL_SIZE: 16 ---*/
#define PBUF_POOL_SIZE 20
/*----- Default Value for PBUF_POOL_BUFSIZE: 592 ---*/
#define PBUF_POOL_BUFSIZE 1560
/*----- Value in opt.h for LWIP_ETHERNET: LWIP_ARP || PPPOE_SUPPORT -*/
#define LWIP_ETHERNET 1
/*----- Value in opt.h for LWIP_DNS_SECURE: (LWIP_DNS_SECURE_RAND_XID | LWIP_DNS_SECURE_NO_MULTIPLE_OUTSTANDING | LWIP_DNS_SECURE_RAND_SRC_PORT) -*/
#define LWIP_DNS_SECURE 7
/*----- Default Value for TCP_WND: 5840 ---*/
#define TCP_WND 16384
/*----- Default Value for TCP_MSS: 536 ---*/
#define TCP_MSS 1460
/*----- Default Value for TCP_SND_BUF: 2920 ---*/
#define TCP_SND_BUF 16384
/*----- Default Value for TCP_SND_QUEUELEN: 46 ---*/
#define TCP_SND_QUEUELEN 2048

Here is my send_jpeg function

void http_send_jpeg(struct tcp_pcb *pcb)
{
	err_t err;

	// Nếu chưa đang gửi JPEG, bắt đầu gửi frame mới
	if (!jpeg_state.sending)
	{
		jpeg_state.sent = 0;
		jpeg_state.sending = true;
		jpeg_state.current_length = jpegLength;

		// Gửi header MJPEG
		char header[128];
		sprintf(header, "--frame\r\nContent-Type: image/jpeg\r\nContent-Length: %lu\r\n\r\n", jpegLength);

		// Kiểm tra buffer trước khi gửi header
		if (tcp_sndbuf(pcb) < strlen(header))
		{
			printf("Not enough buffer for header\n");
			return;
		}

		err = tcp_write(pcb, header, strlen(header), TCP_WRITE_FLAG_COPY);
		if (err != ERR_OK)
		{
			printf("tcp_write header failed: %d\n", err);
			jpeg_state.sending = false;
			return;
		}
	}
	err = ERR_OK;
	// Gửi dữ liệu cho đến khi hết buffer hoặc hết dữ liệu
	while (jpeg_state.sent < jpeg_state.current_length && err == ERR_OK)
	{
		// Tính số byte thực sự sẽ gửi
		uint16_t to_send = min(16384, jpeg_state.current_length - jpeg_state.sent);

		// Gửi dữ liệu
		err = tcp_write(pcb, &jpeg[jpeg_state.sent], to_send, TCP_WRITE_FLAG_COPY);
		if (err != ERR_OK)
		{
			printf("tcp_write JPEG failed at: %lu, error: %d\n", jpeg_state.sent, err);
			tcp_output(pcb);
			return; // Thoát và thử lại sau
		}

		// Chỉ cập nhật số byte đã gửi khi tcp_write thành công
		jpeg_state.sent += to_send;
		if (jpeg_state.sent == jpeg_state.current_length)
		{
			tcp_output(pcb); // Đẩy dữ liệu ngay lập tức
		}
	}
	if (jpeg_state.sent < jpeg_state.current_length)
	{
	}
	else if (tcp_sndbuf(pcb) < 2)
	{
		// Không đủ buffer cho footer, đợi callback tiếp theo
		tcp_output(pcb);
		return;
	}
	else
	{
		err = tcp_write(pcb, "\r\n", 2, TCP_WRITE_FLAG_COPY);
		if (err != ERR_OK)
		{
			printf("tcp_write footer failed: %d\n", err);
			jpeg_state.sending = false;
			return;
		}

		tcp_output(pcb);
		jpeg_state.sending = false; // Đánh dấu đã gửi xong
		jpeg_state.sent = 0;		// Reset vị trí gửi
	}
}

sent_callback:

err_t http_sent_callback(void *arg, struct tcp_pcb *tpcb, u16_t len)
{
	// Sau khi mỗi phần được gửi thành công
	if (tpcb != NULL)
	{
		// Tiếp tục gửi
		http_send_jpeg(tpcb);
	}
	return ERR_OK;
}

And here is my build log

[build] Memory region         Used Size  Region Size  %age Used
[build]              RAM:      190256 B       192 KB     96.77%
[build]           CCMRAM:       32776 B        64 KB     50.01%
[build]            FLASH:      172004 B         2 MB      8.20%
[driver] Build completed: 00:00:09.461
[build] Build finished with exit code 0

Help me please. I spent too much time on this MJPEG server and still cannot figure it out.