Using the info i was able to gleen from here - MACRAW Application Note? - #3 by suhwan
I’ve been able to implement a MACRAW driver that passes the data to the FreeRTOS TCP stack and i thought i had it all working. My plan was just to use the driver to pass one packet at a time to the FreeRTOS stack. Here is the code i use to try and receive only 1 packet at a time. It works for DHCP and dns and all my testing was looking good. But upon making my first TCP connection [to an mqtt server] it returns a “data_len” [see code] of around 20000 to 65000. How can i be receiving a packet that large if my MTU is 1526?
If it is reporting the full length instead of the packet length I’m emotionally destroyed. I can’t possibly allocate 20kb of ram. And i’ve no idea how to retrieve keeping alignment with the frames so the FreeRTOS stack is happy.
Please Help
//the point here is to get the the ptr to the start of the ethernet packet and return the packet length.
//must try to keep buffers in alignment. 
uint16_t macraw_prep(uint8_t sn, uint16_t tot_len)
{
uint16_t data_len = 0;
uint16_t ptr = 0;
uint32_t addrsel = 0;
ptr = getSn_RX_RD(sn);
addrsel = ((uint32_t)ptr << 8) + (WIZCHIP_RXBUF_BLOCK(sn) << 3);
data_len = WIZCHIP_READ(addrsel);
ptr++;
addrsel = ((uint32_t)ptr << 8) + (WIZCHIP_RXBUF_BLOCK(sn) << 3);
data_len = ((data_len<<8) + WIZCHIP_READ(addrsel)) - 2;
ptr++;
if(data_len > 1536)
{
//recommand : close and open - something went wrong to get here
setSn_CR(sn,Sn_CR_CLOSE);
setSn_MR(sn, (Sn_MR_MACRAW | (0 & 0xF0)));
setSn_CR(sn,Sn_CR_OPEN);
return 0;
}
if(data_len > getSn_RX_RSR(sn))
{
//not a full packet in buffer
return 0;
}
setSn_RX_RD(sn,ptr);
setSn_CR(sn,Sn_CR_RECV); // this should make the new pointer stick.
return data_len;
}
