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Now that the class instance has been correctly initialized, it’s time to exchange data. PHDC offers 4 functions to do so. Table - PHDC Communication API Summary summarizes the communication functions provided by the PHDC implementation. See the PHDC API Reference for a complete API reference.
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With Metadata Preamble
Via the preamble enabled callback, the application will be notified once the host enables the metadata preamble. If metadata preambles are enabled, you should use the following procedure to perform a read:
- Call
USBD_PHDC_. Device expects metadata preamble from the host. This function will return opaque data and the number of incoming transfers that the host specified. Note that if the host disables preamble while the application is pending on that function, it will immediately return with error “PreambleRd()USBD_ERR_OS_ABORT”. - Call
USBD_PHDC_Rd()a number of times corresponding to the number of incoming transfers returned byUSBD_PHDC_. The application must ensure that the buffer provided to the function is large enough to accommodate all the data. Otherwise, synchronization issues might happen. Note that if the host enables preamble while the application is pending on that function, it will immediately return with error “PreambleRd()USBD_ERR_OS_ABORT”.
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CPU_INT16U App_USBD_PHDC_Rd(CPU_INT08U class_nbr,
CPU_INT08U *p_data_opaque_buf
CPU_INT08U *p_data_opaque_len,
CPU_INT08U *p_buf,
USBD_ERR *p_err)
{
CPU_INT08U nbr_xfer;
CPU_INT16U xfer_len;
CPU_INT08U i;
*p_data_opaque_len = USBD_PHDC_PreambleRd( class_nbr, (1)
(void *)p_data_opaque_buf, (2)
USBD_PHDC_CFG_DATA_OPAQUE_MAX_LEN,
&nbr_xfer, (3)
0, (4)
p_err);
for (i = 0u; i < nbr_xfer; i++) { (5)
xfer_len = USBD_PHDC_Rd( class_nbr,
(void *)p_buf, (6)
APP_USBD_PHDC_ITEM_DATA_LEN_MAX,
0, (4)
p_err);
/* Handle received data. */
}
return (xfer_len);
} |
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(1) The class instance number obtained with (2) Buffer that will contain opaque data. The application must ensure that the buffer provided is large enough to accommodate all the data. Otherwise, synchronization issues might happen. (3) Variable that will contain the number of following transfers to which this preamble applies. (4) In order to avoid an infinite blocking situation, a timeout expressed in milliseconds can be specified. A value of ‘0’ makes the application task wait forever. (5) Read all the USB transfers to which the preamble applies. (6) Buffer that will contain the data. The application must ensure that the buffer provided is large enough to accommodate all the data. Otherwise, synchronization issues might happen. |
You should use the following procedure to perform a write:
- Call
USBD_PHDC_. The host expects metadata preamble from the device. The application will have to specify opaque data, transfer’s QoS (see Table - Listing of QoS Bins), and a number of following transfers to which the selected QoS applies.PreambleWr() - Call
USBD_PHDC_Wr()a number of times corresponding to the number of transfers following the preamble.
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CPU_INT16U App_USBD_PHDC_Wr(CPU_INT08U class_nbr,
LATENCY_RELY_FLAGS latency_rely,
CPU_INT08U nbr_xfer,
CPU_INT08U *p_data_opaque_buf
CPU_INT08U data_opaque_buf_len,
CPU_INT08U *p_buf,
CPU_INT08U buf_len,
USBD_ERR *p_err)
{
CPU_INT08U i;
(void)USBD_PHDC_PreambleWr( class_nbr, (1)
(void *)p_data_opaque_buf, (2)
data_opaque_buf_len,
latency_rely, (3)
nbr_xfer, (4)
0, (5)
p_err);
for (i = 0u; i < nbr_xfer; i++) { (6)
/* Prepare data to send. */
xfer_len = USBD_PHDC_Wr( class_nbr, (1)
(void *)p_buf, (7)
buf_len,
latency_rely, (3)
0,
p_err);
}
} |
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(1) The class instance number obtained with (2) Buffer that contains opaque data. (3) Latency / reliability (QoS) of the following transfer(s). (4) Variable that contains the number of following transfers to which this preamble will apply. (5) In order to avoid an infinite blocking situation, a timeout expressed in milliseconds can be specified. A value of ‘0’ makes the application task wait forever. (6) Write all the USB transfers to which the preamble will apply. (7) Buffer that contains the data. |
Without Metadata Preamble
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