//*****************************************************************************
//
// Schedule the next packet transmission to the host if data remains to be
// sent.
//
// \param psBuffer points to the buffer from which a packet transmission is
// to be scheduled.
//
// This function checks to determine whether the lower layer is capable of
// accepting a new packet for transmission and, if so, schedules the next
// packet transmission if data remains in the buffer.
//
// \return None.
//
//*****************************************************************************
static void
ScheduleNextTransmission(const tUSBBuffer *psBuffer)
{
tUSBBufferVars *psVars;
unsigned long ulPacket, ulSpace, ulTotal;
//
// Get a pointer to our workspace variables.
//
psVars = psBuffer->pvWorkspace;
//
// Ask the lower layer if it has space to accept another packet of data.
//
ulPacket = psBuffer->pfnAvailable(psBuffer->pvHandle);
//
// If we were returned something other than zero, we can write that number
// of bytes to the lower layer.
//
if(ulPacket)
{
//
// How much contiguous data do we have in the buffer?
//
ulSpace = USBRingBufContigUsed(&psVars->sRingBuf);
//
// How much total data do we have in the buffer?
//
ulTotal = USBRingBufUsed(&psVars->sRingBuf);
//
// Write the contiguous bytes to the lower layer assuming there is
// something to send.
//
if(ulSpace)
{
//
// Determine the maximum sized block we can send in this transfer.
//
ulSpace = (ulSpace < ulPacket) ? ulSpace : ulPacket;
//
// Call the lower layer to send the new packet. If the current
// data spans the buffer wrap, tell the lower layer that it can
// expect a second call to fill the whole packet before it
// transmits it.
//
psBuffer->pfnTransfer(psBuffer->pvHandle,
(psVars->sRingBuf.pucBuf +
psVars->sRingBuf.ulReadIndex), ulSpace,
(((ulSpace < ulPacket) &&
(ulSpace < ulTotal)) ? false : true));
//
// Do we need to send a second part to fill out the packet? This
// will occur if the current packet spans the buffer wrap.
//
if((ulSpace < ulPacket) && (ulSpace < ulTotal))
{
//
// The packet straddled the wrap. How much space remains in
// the packet?
//
ulPacket -= ulSpace;
//
// How much data can we actually send?
//
ulSpace = ulTotal - ulSpace;
ulSpace = (ulSpace > ulPacket) ? ulPacket : ulSpace;
psBuffer->pfnTransfer(psBuffer->pvHandle,
psVars->sRingBuf.pucBuf, ulSpace, true);
}
}
//
// Don't update the ring buffer read index yet. We do this once we are
// sure the packet was correctly transmitted.
//
}
}
//*****************************************************************************
//
// Schedule the next packet transmission to the host if data remains to be
// sent.
//
// \param psBuffer points to the buffer from which a packet transmission is
// to be scheduled.
//
// This function checks to determine whether the lower layer is capable of
// accepting a new packet for transmission and, if so, schedules the next
// packet transmission if data remains in the buffer.
//
// \return None.
//
//*****************************************************************************
static void
ScheduleNextTransmission(tUSBBuffer *psBuffer)
{
uint32_t ui32Packet, ui32Space, ui32Total, ui32Sent;
//
// Ask the lower layer if it has space to accept another packet of data.
//
ui32Packet = psBuffer->pfnAvailable(psBuffer->pvHandle);
//
// If we were returned something other than zero, we can write that number
// of bytes to the lower layer.
//
if(ui32Packet)
{
//
// How much contiguous data do we have in the buffer?
//
ui32Space = USBRingBufContigUsed(&psBuffer->sPrivateData.sRingBuf);
//
// How much total data do we have in the buffer?
//
ui32Total = USBRingBufUsed(&psBuffer->sPrivateData.sRingBuf);
//
// How much data will we be sending as a result of this call?
//
ui32Sent = (ui32Packet < ui32Total) ? ui32Packet : ui32Total;
//
// Write the contiguous bytes to the lower layer assuming there is
// something to send.
//
if(ui32Space)
{
//
// There is data available to send. Update our state to indicate
// the amount we will be sending in this packet.
//
psBuffer->sPrivateData.ui32LastSent = ui32Sent;
//
// Determine the maximum sized block we can send in this transfer.
//
ui32Space = (ui32Space < ui32Packet) ? ui32Space : ui32Packet;
//
// Call the lower layer to send the new packet. If the current
// data spans the buffer wrap, tell the lower layer that it can
// expect a second call to fill the whole packet before it
// transmits it.
//
psBuffer->pfnTransfer(psBuffer->pvHandle,
(psBuffer->sPrivateData.sRingBuf.pui8Buf +
psBuffer->sPrivateData.sRingBuf.ui32ReadIndex),
ui32Space,
(((ui32Space < ui32Packet) &&
(ui32Space < ui32Total)) ? false : true));
//
// Do we need to send a second part to fill out the packet? This
// will occur if the current packet spans the buffer wrap.
//
if((ui32Space < ui32Packet) && (ui32Space < ui32Total))
{
//
// The packet straddled the wrap. How much space remains in
// the packet?
//
ui32Packet -= ui32Space;
//
// How much data can we actually send?
//
ui32Space = ui32Total - ui32Space;
ui32Space = (ui32Space > ui32Packet) ? ui32Packet : ui32Space;
psBuffer->pfnTransfer(psBuffer->pvHandle,
psBuffer->sPrivateData.sRingBuf.pui8Buf,
ui32Space, true);
}
}
else
{
//
// There is no data to send. Did we last send a full packet?
//
if(psBuffer->sPrivateData.ui32LastSent == ui32Packet)
{
//
// Yes - if necessary, send a zero-length packet back to the
// host to complete the last transaction.
//
if(psBuffer->sPrivateData.ui32Flags & USB_BUFFER_FLAG_SEND_ZLP)
{
psBuffer->sPrivateData.ui32LastSent = 0;
psBuffer->pfnTransfer(psBuffer->pvHandle,
psBuffer->sPrivateData.sRingBuf.pui8Buf,
0, true);
}
}
}
//
// Don't update the ring buffer read index yet. We do this once we are
// sure the packet was correctly transmitted.
//
}
}