Transferring Data
Other versions of this page are also available for the following:
.gif "A hyphen indicates that the information in this topic is not relevant for this platform, or that the platform does not support the API that is listed.")
.gif "A checkmark indicates that the information in this topic is relevant for this platform, and that any API listed is also supported on this platform.")
8/28/2008
To avoid data copying, the protocol stack uses two static buffers: one for reading and the other for writing. These buffers are given to the HCI_ReadPacket and HCI_WritePacket functions, respectively.
The data transfer structure is organized in such a way that headers can be easily pre-allocated on the way down or stripped on the way up. The HCI then goes into a read loop on one thread calling the HCI_ReadPacket function.
The buffers are exchanged using the following form.
struct BD_BUFFER {
int cSize;
int cStart;
int cEnd;
BD_BUFFER_FREE pFree;
int fMustCopy;
unsigned char *pBuffer;
};
Of interest to HCI transport here are only three members:
- cSize,whichdefines the size of pBuffer
- cStart, which is the offset of valid information in pBuffer
- cEnd, which is the end of valid information in pBuffer
HCI_ReadPacket is given a buffer in which cSize is not smaller than the one requested in the HCI_ReadHciParameters response. cStart is set to 0 and cEnd is set to be equal to cSize. Before HCI_ReadPacket returns, it is allowed to use this buffer however it pleases. On return, the data between cStart and cEnd MUST contain a valid Bluetooth HCI packet.
The HCI_WritePacket function is given a buffer where cStart is set to the beginning of the HCI packet. The spaces between 0 and cStart and between cEnd and cSize will be big enough to accommodate the transport header and trailer as requested by HCI_ReadHciParameters. HCI_WritePacket can use these spaces to put its own information in it.
The packet type is returned in *peType and can be DATA_PACKET_ACL, DATA_PACKET_SCO or EVENT_PACKET.
If communication with the Bluetooth controller fails because of hardware failure or the controller has been ejected from the device, HCI_ReadPacket must fail with a 0 return code. The HCI layer will then shut itself down until indicated by the transport layer that the hardware is available using the callback.
// HCI_ReadPacket MUST return 4-bytes aligned cStart in its buffer
// HCI_ReadPacket and HCI_WritePacket WILL change cStart and cEnd of the
// buffer, but WILL NOT change any other data.
enum HCI_TYPE {
COMMAND_PACKET = 1,
DATA_PACKET_ACL = 2,
DATA_PACKET_SCO = 3,
EVENT_PACKET = 4,
ETYPE_FINISH = 5
};
int HCI_ReadPacket (HCI_TYPE *peType, BD_BUFFER *pInBuffer);
int HCI_WritePacket (HCI_TYPE eType, BD_BUFFER *pOutBuffer);