diff options
Diffstat (limited to 'libusb/io.c')
-rw-r--r-- | libusb/io.c | 76 |
1 files changed, 76 insertions, 0 deletions
diff --git a/libusb/io.c b/libusb/io.c index 0b876d1..f50bdf3 100644 --- a/libusb/io.c +++ b/libusb/io.c @@ -1053,6 +1053,82 @@ printf("completed!\n"); } #endif +/** \ingroup asyncio + * Convenience function to locate the position of an isochronous packet + * within the buffer of an isochronous transfer. + * + * This is a thorough function which loops through all preceding packets, + * accumulating their lengths to find the position of the specified packet. + * Typically you will assign equal lengths to each packet in the transfer, + * and hence the above method is sub-optimal. You may wish to use + * libusb_get_iso_packet_buffer_simple() instead. + * + * \param transfer a transfer + * \param packet the packet to return the address of + * \returns the base address of the packet buffer inside the transfer buffer, + * or NULL if the packet does not exist. + * \see libusb_get_iso_packet_buffer_simple() + */ +unsigned char *libusb_get_iso_packet_buffer( + struct libusb_transfer *transfer, unsigned int packet) +{ + int i; + size_t offset = 0; + int _packet; + + /* oops..slight bug in the API. packet is an unsigned int, but we use + * signed integers almost everywhere else. range-check and convert to + * signed to avoid compiler warnings. FIXME for libusb-2. */ + if (packet > INT_MAX) + return NULL; + _packet = packet; + + if (_packet >= transfer->num_iso_packets) + return NULL; + + for (i = 0; i < _packet; i++) + offset += transfer->iso_packet_desc[i].length; + + return transfer->buffer + offset; +} + +/** \ingroup asyncio + * Convenience function to locate the position of an isochronous packet + * within the buffer of an isochronous transfer, for transfers where each + * packet is of identical size. + * + * This function relies on the assumption that every packet within the transfer + * is of identical size to the first packet. Calculating the location of + * the packet buffer is then just a simple calculation: + * <tt>buffer + (packet_size * packet)</tt> + * + * Do not use this function on transfers other than those that have identical + * packet lengths for each packet. + * + * \param transfer a transfer + * \param packet the packet to return the address of + * \returns the base address of the packet buffer inside the transfer buffer, + * or NULL if the packet does not exist. + * \see libusb_get_iso_packet_buffer() + */ +unsigned char *libusb_get_iso_packet_buffer_simple( + struct libusb_transfer *transfer, unsigned int packet) +{ + int _packet; + + /* oops..slight bug in the API. packet is an unsigned int, but we use + * signed integers almost everywhere else. range-check and convert to + * signed to avoid compiler warnings. FIXME for libusb-2. */ + if (packet > INT_MAX) + return NULL; + _packet = packet; + + if (_packet >= transfer->num_iso_packets) + return NULL; + + return transfer->buffer + (transfer->iso_packet_desc[0].length * _packet); +} + int usbi_io_init(struct libusb_context *ctx) { int r; |