Compiler/EK-TM4C1294XL: EK-TM4c1294NCPDT

Dear Charles, 

Examples looks good, but still i am confused of how to implement this in my actual code. 

I am attaching below my code. Might be if you can give me some hint. 

The Echo implementation: 

//
// Main Application Loop.
//
i32PeriodicTimer = 0;
i32ARPTimer = 0;
while(true)
{
//
// Wait for an event to occur. This can be either a System Tick event,
// or an RX Packet event.
//
while(!g_ui32Flags)
{
}

//
// If SysTick, Clear the SysTick interrupt flag and increment the
// timers.
//
if(HWREGBITW(&g_ui32Flags, FLAG_SYSTICK) == 1)
{
HWREGBITW(&g_ui32Flags, FLAG_SYSTICK) = 0;
i32PeriodicTimer += SYSTICKMS;
i32ARPTimer += SYSTICKMS;
}

//
// Check for an RX Packet and read it.
//
if(HWREGBITW(&g_ui32Flags, FLAG_RXPKT))
{
//
// Clear the RX Packet event flag.
//
HWREGBITW(&g_ui32Flags, FLAG_RXPKT) = 0;

// Get the packet and set uip_len for uIP stack usage.
//
uip_len = (unsigned short)PacketReceive(EMAC0_BASE, uip_buf,
sizeof(g_pui8UIPBuffer));

//
// Process incoming IP packets here.
//
if(BUF->type == htons(UIP_ETHTYPE_IP))
{
// check if UDP protocol used
if (IPBUF->proto == 0x11) {

// swap MAC addresses

MACaddr[0] = IPBUF->ethhdr.src.addr[0];
MACaddr[1] = IPBUF->ethhdr.src.addr[1];
MACaddr[2] = IPBUF->ethhdr.src.addr[2];
MACaddr[3] = IPBUF->ethhdr.src.addr[3];
MACaddr[4] = IPBUF->ethhdr.src.addr[4];
MACaddr[5] = IPBUF->ethhdr.src.addr[5];

IPBUF->ethhdr.src.addr[0] = IPBUF->ethhdr.dest.addr[0];
IPBUF->ethhdr.src.addr[1] = IPBUF->ethhdr.dest.addr[1];
IPBUF->ethhdr.src.addr[2] = IPBUF->ethhdr.dest.addr[2];
IPBUF->ethhdr.src.addr[3] = IPBUF->ethhdr.dest.addr[3];
IPBUF->ethhdr.src.addr[4] = IPBUF->ethhdr.dest.addr[4];
IPBUF->ethhdr.src.addr[5] = IPBUF->ethhdr.dest.addr[5];

IPBUF->ethhdr.dest.addr[0] = MACaddr[0];
IPBUF->ethhdr.dest.addr[1] = MACaddr[1];
IPBUF->ethhdr.dest.addr[2] = MACaddr[2];
IPBUF->ethhdr.dest.addr[3] = MACaddr[3];
IPBUF->ethhdr.dest.addr[4] = MACaddr[4];
IPBUF->ethhdr.dest.addr[5] = MACaddr[5];

// swap IP address

IPBUF->destipaddr[0] = IPBUF->srcipaddr[0];
IPBUF->destipaddr[1] = IPBUF->srcipaddr[1];
IPBUF->srcipaddr [0] = uip_hostaddr[0];
IPBUF->srcipaddr [1] = uip_hostaddr[1];
}
else {
uip_len = 0;
}
PacketTransmit(EMAC0_BASE, uip_buf, uip_len);
uip_len = 0;

}

First of all i have to send the packet

from the PC to MC on Port 2048 with some message, 

and then i will toggle the source and destination address in order to send the packet back from

MC to PC using a different Port which for e.g 2049 with different message length. 

I am a bit confused, should i define in the echo the port number because i am using packet sender for it. 

What i need is to run the main loop which first sends a packet from Point A to B and then wait during which i can send a packet from Point B to A another Packet. 

How should i proceed with this???

In the enet_uip example: 

1. uIP uses a single buffer, but the MAC needs a minimum of 3 receive descriptors to operate

#define NUM_TX_DESCRIPTORS 3
#define NUM_RX_DESCRIPTORS 3

I don't get why MAC hardware need a minimum of 3 receive descriptors??

2. How the intterupt handler for SysTick interrupt works 

void
SysTickIntHandler(void)
{
//
// Increment the system tick count.
//
g_ui32TickCounter++;

//
// Indicate that a SysTick interrupt has occurred.
//
HWREGBITW(&g_ui32Flags, FLAG_SYSTICK) = 1;

I don't get what this HWREGBITW and the equal to 1 means in this case?? and also how is the interrupt called ?

3. Then there is a function  void EthernetIntHandler(void)  I have not seen this function to be used in main. Can you explain when and how it works?

Hi Charles, 

Yes i went throught the LwIP UDP example. 

Actually i started couple of weeks ago with uIP therefore i am using this example. 

Second i don't see any DMA in the LwIP where i should be able to Receive packet and transmit packet and no buffers. Correct me if i am wrong. In LwIP what it is doing is receving the packets and sending it back to specified port and a new IP. 

Third, what i want to do is that i have send the packet and the packet is received and copied to the buffer. Now the packet is in the buffer,

I want to do know is to extend the payload in the buffer and change the length before transmitting it back from the MC to PC. 

Packet received and stored in the uIP_buf and transmitted from PC to MC. 

For example a photo attached: UDP packet 

1. Source port

2. Destination port. 

3. Length

4. Check sum 

5. Data 

this can be seen in my picture. 

Now this payload (buffer data) is in microcontroller software and i want to only change the payload of the data packet and specify the port number on which i want to send. And then transmit it back to the PC. 

Before Transmitting the packet the buffer should have only the data and the length change e.g from (Test_0) to (Test_4321_echo)  plus the port number.

Can you help me how should i approach to this problem. I tried some example but don't works.