TM4C1294NCPDT: TM4C1294NCPDT

I don't know what else did you change. Note the example is only a simple webserver. You probably change something other than just NUM_RX_DESCRIPTORS . 

I change both the TX and RX to 12 and run the example. I don't see any problem. 

#define NUM_TX_DESCRIPTORS 12
#define NUM_RX_DESCRIPTORS 12

As I mentioned, uIP only uses one buffer even if you reserve 3 or 12 will not help per comments from the example. If you look at 12 descriptors, they all point to the same buffer. 

I will suggest you use wireshark to understand your problem.

Hi,

I modified the uip code sections with the example provided in Tivaware Userguide. But if you see the code section in userguide there is small (yet problematic) error with TX and RX interchanged for the buffer as in image below. 

I corrected this interchange of TX and RX. Even then it was not able receive and transmit packets. But when I checked with debug, 12 buffers were assigned as it is shown in the earlier reply. I'm attaching the code section of buffers and descriptor initialization. 

//*****************************************************************************
//
// Ethernet DMA descriptors.
//
// The MAC hardware needs a minimum of 3 receive descriptors to operate. The
// number used will be application-dependent and should be tuned for best
// performance.
//
//*****************************************************************************
#define NUM_TX_DESCRIPTORS 3
#define NUM_RX_DESCRIPTORS 24
tEMACDMADescriptor g_psRxDescriptor[NUM_RX_DESCRIPTORS];
tEMACDMADescriptor g_psTxDescriptor[NUM_TX_DESCRIPTORS];
uint32_t g_ui32RxDescIndex;
uint32_t g_ui32TxDescIndex;

#define RX_BUFFER_SIZE 1536
uint8_t g_ppui8RxBuffer[NUM_RX_DESCRIPTORS][RX_BUFFER_SIZE];



void
InitDescriptors(uint32_t ui32Base)
{
		uint32_t ui32Loop;
	
		// Initialize each of the transmit descriptors. Note that we leave the
		// buffer pointer and size empty and the OWN bit clear here since we have
		// not set up any transmissions yet.
		//
		for(ui32Loop = 0; ui32Loop < NUM_TX_DESCRIPTORS; ui32Loop++) {
			g_psTxDescriptor[ui32Loop].ui32Count = DES1_TX_CTRL_SADDR_INSERT;
			g_psTxDescriptor[ui32Loop].DES3.pLink = (ui32Loop == (NUM_TX_DESCRIPTORS - 1)) ?
											g_psTxDescriptor : &g_psTxDescriptor[ui32Loop + 1];
			g_psTxDescriptor[ui32Loop].ui32CtrlStatus = (DES0_TX_CTRL_LAST_SEG | DES0_TX_CTRL_FIRST_SEG |
					DES0_TX_CTRL_INTERRUPT | DES0_TX_CTRL_CHAINED |
					DES0_TX_CTRL_IP_HDR_CHKSUM);
		}
		//
		// Initialize each of the receive descriptors. We clear the OWN bit here
		// to make sure that the receiver doesn t start writing anything
		// immediately.
		//
		for(ui32Loop = 0; ui32Loop < NUM_RX_DESCRIPTORS; ui32Loop++)
		{
		g_psRxDescriptor[ui32Loop].ui32CtrlStatus = 0;
		g_psRxDescriptor[ui32Loop].ui32Count = (DES1_RX_CTRL_CHAINED |
										(RX_BUFFER_SIZE << DES1_RX_CTRL_BUFF1_SIZE_S));
		g_psRxDescriptor[ui32Loop].pvBuffer1 = g_ppui8RxBuffer[ui32Loop];
		g_psRxDescriptor[ui32Loop].DES3.pLink = (ui32Loop == (NUM_RX_DESCRIPTORS - 1)) ?
					g_psRxDescriptor : &g_psRxDescriptor[ui32Loop + 1];
		}
		//
		// Set the descriptor pointers in the hardware.
		//
		EMACRxDMADescriptorListSet(ui32Base, g_psRxDescriptor);
		EMACTxDMADescriptorListSet(ui32Base, g_psTxDescriptor);
		//
		// Start from the beginning of both descriptor chains. We actually set
		// the transmit descriptor index to the last descriptor in the chain
		// since it will be incremented before use and this means the first
		// transmission we perform will use the correct descriptor.
		//
		g_ui32RxDescIndex = 0;
		g_ui32TxDescIndex = NUM_TX_DESCRIPTORS - 1;
}

Then I copied the emac.c and emac.h into my sourcecode folder and added these file to my project. Then compiled and downloaded. Surprisingly it worked. 

Thanks for the support extended.