/**
* @brief Prepares DMA Tx descriptors to transmit an ethernet frame
* @param FrameLength : length of the frame to send
* @retval error status
*/
uint32_t ETH_Prepare_Transmit_Descriptors(u16 FrameLength)
{
uint32_t buf_count =0, size=0,i=0;
__IO ETH_DMADESCTypeDef *DMATxDesc;

/* Check if the descriptor is owned by the ETHERNET DMA (when set) or CPU (when reset) */
if((DMATxDescToSet->Status & ETH_DMATxDesc_OWN) != (u32)RESET)
{
/* Return ERROR: OWN bit set */
return ETH_ERROR;
}

DMATxDesc = DMATxDescToSet;

if (FrameLength > ETH_TX_BUF_SIZE)
{
buf_count = FrameLength/ETH_TX_BUF_SIZE;
if (FrameLength%ETH_TX_BUF_SIZE) buf_count++;
}
else buf_count =1;

if (buf_count ==1)
{
/*set LAST and FIRST segment */
DMATxDesc->Status |=ETH_DMATxDesc_FS|ETH_DMATxDesc_LS;
/* Set frame size */
DMATxDesc->ControlBufferSize = (FrameLength & ETH_DMATxDesc_TBS1);
/* Set Own bit of the Tx descriptor Status: gives the buffer back to ETHERNET DMA */
DMATxDesc->Status |= ETH_DMATxDesc_OWN;
DMATxDesc= (ETH_DMADESCTypeDef *)(DMATxDesc->Buffer2NextDescAddr);
}
else
{
for (i=0; i< buf_count; i++)
{
/* Clear FIRST and LAST segment bits */
DMATxDesc->Status &= ~(ETH_DMATxDesc_FS | ETH_DMATxDesc_LS);

if (i==0)
{
/* Setting the first segment bit */
DMATxDesc->Status |= ETH_DMATxDesc_FS;
}

/* Program size */
DMATxDesc->ControlBufferSize = (ETH_TX_BUF_SIZE & ETH_DMATxDesc_TBS1);

if (i== (buf_count-1))
{
/* Setting the last segment bit */
DMATxDesc->Status |= ETH_DMATxDesc_LS;
size = FrameLength - (buf_count-1)*ETH_TX_BUF_SIZE;
DMATxDesc->ControlBufferSize = (size & ETH_DMATxDesc_TBS1);
}

/* Set Own bit of the Tx descriptor Status: gives the buffer back to ETHERNET DMA */
DMATxDesc->Status |= ETH_DMATxDesc_OWN;

DMATxDesc = (ETH_DMADESCTypeDef *)(DMATxDesc->Buffer2NextDescAddr);
}
}

DMATxDescToSet = DMATxDesc;

/* When Tx Buffer unavailable flag is set: clear it and resume transmission */
if ((ETH->DMASR & ETH_DMASR_TBUS) != (u32)RESET)
{
/* Clear TBUS ETHERNET DMA flag */
ETH->DMASR = ETH_DMASR_TBUS;
/* Resume DMA transmission*/
ETH->DMATPDR = 0;
}

/* Return SUCCESS */
return ETH_SUCCESS;
}

static err_t low_level_output(struct netif *netif, struct pbuf *p)
{
static xSemaphoreHandle xTxSemaphore = NULL;
struct pbuf *q;
u8 *buffer ;
__IO ETH_DMADESCTypeDef *DmaTxDesc;
uint16_t framelength = 0;
uint32_t bufferoffset = 0;
uint32_t byteslefttocopy = 0;
uint32_t payloadoffset = 0;

if (xTxSemaphore == NULL)
{
vSemaphoreCreateBinary (xTxSemaphore);
}

if (xSemaphoreTake(xTxSemaphore, netifGUARD_BLOCK_TIME))
{
DmaTxDesc = DMATxDescToSet;
buffer = (u8 *)(DmaTxDesc->Buffer1Addr);
bufferoffset = 0;

for(q = p; q != NULL; q = q->next)
{
if((DmaTxDesc->Status & ETH_DMATxDesc_OWN) != (u32)RESET)
{
goto error;
}

/* Get bytes in current lwIP buffer */
byteslefttocopy = q->len;
payloadoffset = 0;

/* Check if the length of data to copy is bigger than Tx buffer size*/
while( (byteslefttocopy + bufferoffset) > ETH_TX_BUF_SIZE )
{
/* Copy data to Tx buffer*/
memcpy( (u8_t*)((u8_t*)buffer + bufferoffset), (u8_t*)((u8_t*)q->payload + payloadoffset), (ETH_TX_BUF_SIZE - bufferoffset) );

/* Point to next descriptor */
DmaTxDesc = (ETH_DMADESCTypeDef *)(DmaTxDesc->Buffer2NextDescAddr);

/* Check if the buffer is available */
if((DmaTxDesc->Status & ETH_DMATxDesc_OWN) != (u32)RESET)
{
goto error;
}

buffer = (u8 *)(DmaTxDesc->Buffer1Addr);

byteslefttocopy = byteslefttocopy - (ETH_TX_BUF_SIZE - bufferoffset);
payloadoffset = payloadoffset + (ETH_TX_BUF_SIZE - bufferoffset);
framelength = framelength + (ETH_TX_BUF_SIZE - bufferoffset);
bufferoffset = 0;
}

/* Copy the remaining bytes */
memcpy( (u8_t*)((u8_t*)buffer + bufferoffset), (u8_t*)((u8_t*)q->payload + payloadoffset), byteslefttocopy );
bufferoffset = bufferoffset + byteslefttocopy;
framelength = framelength + byteslefttocopy;
}

/* Prepare transmit descriptors to give to DMA*/
ETH_Prepare_Transmit_Descriptors(framelength);

/* Give semaphore and exit */
error:

xSemaphoreGive(xTxSemaphore);
}

return ERR_OK;
}

static err_t low_level_output(struct netif *netif, struct pbuf *p)
{
err_t errval;
struct pbuf *q;
u8 *buffer = (u8 *)(DMATxDescToSet->Buffer1Addr);
__IO ETH_DMADESCTypeDef *DmaTxDesc;
uint16_t framelength = 0;
uint32_t bufferoffset = 0;
uint32_t byteslefttocopy = 0;
uint32_t payloadoffset = 0;

DmaTxDesc = DMATxDescToSet;
bufferoffset = 0;

/* copy frame from pbufs to driver buffers */
for(q = p; q != NULL; q = q->next)
{
/* Is this buffer available? If not, goto error */
if((DmaTxDesc->Status & ETH_DMATxDesc_OWN) != (u32)RESET)
{
errval = ERR_BUF;
goto error;
}

/* Get bytes in current lwIP buffer */
byteslefttocopy = q->len;
payloadoffset = 0;

/* Check if the length of data to copy is bigger than Tx buffer size*/
while( (byteslefttocopy + bufferoffset) > ETH_TX_BUF_SIZE )
{
/* Copy data to Tx buffer*/
memcpy( (u8_t*)((u8_t*)buffer + bufferoffset), (u8_t*)((u8_t*)q->payload + payloadoffset), (ETH_TX_BUF_SIZE - bufferoffset) );

/* Point to next descriptor */
DmaTxDesc = (ETH_DMADESCTypeDef *)(DmaTxDesc->Buffer2NextDescAddr);

/* Check if the buffer is available */
if((DmaTxDesc->Status & ETH_DMATxDesc_OWN) != (u32)RESET)
{
errval = ERR_USE;
goto error;
}

buffer = (u8 *)(DmaTxDesc->Buffer1Addr);

byteslefttocopy = byteslefttocopy - (ETH_TX_BUF_SIZE - bufferoffset);
payloadoffset = payloadoffset + (ETH_TX_BUF_SIZE - bufferoffset);
framelength = framelength + (ETH_TX_BUF_SIZE - bufferoffset);
bufferoffset = 0;
}

/* Copy the remaining bytes */
memcpy( (u8_t*)((u8_t*)buffer + bufferoffset), (u8_t*)((u8_t*)q->payload + payloadoffset), byteslefttocopy );
bufferoffset = bufferoffset + byteslefttocopy;
framelength = framelength + byteslefttocopy;
}

/* Note: padding and CRC for transmitted frame
are automatically inserted by DMA */

/* Prepare transmit descriptors to give to DMA*/
ETH_Prepare_Transmit_Descriptors(framelength);

errval = ERR_OK;

error:

/* When Transmit Underflow flag is set, clear it and issue a Transmit Poll Demand to resume transmission */
if ((ETH->DMASR & ETH_DMASR_TUS) != (uint32_t)RESET)
{
/* Clear TUS ETHERNET DMA flag */
ETH->DMASR = ETH_DMASR_TUS;

/* Resume DMA transmission*/
ETH->DMATPDR = 0;
}
return errval;
}