W5500 - Need help with UDP Rx buffer pointer wrap-around

Question

Hi, I am working with the UDP protocol setting. I am able to receive UDP packets correctly until the Sn_RX_RD pointer reaches the end of the 2K RX buffer (I’m using the default 2K, and using Socket 0). Here is the pseudocode of what I am doing: rx_len = getSn_RX_RSR() // get packet, returns when non-zero rx_len rx_ptr = getSn_RX_RD() // get Rx pointer buffer = readData(rx_ptr) // read data at pointer address rx_ptr += rx_len // calculate new pointer if (rx_ptr > 0x07ff) // check for wrap-around rx_ptr -=0x07ff setSn_RX_RD() // update pointer setRECV() // notify receive complete It works up until the next packet that arrives after the wrap-around. When that packet arrives, the getSn_RX_RSR() function returns 0x07ff and “gets stuck” at 0x07ff. So the W5500 reports that a packet is continuously arriving with length 0x07ff. Any hints on how to handle the wrap-around logic – or perhaps it is something else I’ve missed? Thanks, Richard.

Eugeny · Answer

Take a look into W5100 datasheet pages 44-45. You must use all 16 bits of the pointer to update RX_RD, while for actual data pointing you must use window-masked pointer.

Eugeny · Answer

Wizboy: can/should the value of this register be used to calculate the new Sn_RX_RD pointer instead of adding the received packet length No. RX_WR is being used by the chip internally, and can change in any moment, and the value you read may be just invalid (because value in register may change between reads of two bytes). You must do exactly as described in the datasheet, even if it looks not the easiest way to proceed.