A–11
A.4.3.6.2 USB Out Endpoint – Isochronous Configuration Byte
This section defines the functionality of the bits in the USB out endpoint configuration byte for isochronous endpoints.
Bit 7 6 5 4 3 2 1 0
Mnemonic OEPEN ISO OVF BPS4 BPS3 BPS2 BPS1 BPS0
Type R/W R/W R/W R/W R/W R/W R/W R/W
BIT MNEMONIC NAME DESCRIPTION
7 OEPEN Endpoint enable The endpoint enable bit is set to a 1 by the MCU to enable the out endpoint.
6 ISO Isochronous endpoint The isochronous endpoint bit is set to a 1 by the MCU to specify the use of a
particular out endpoint for isochronous transactions. This bit should be cleared to a 0
by the MCU for a particular out endpoint to be used for control, interrupt, or bulk
transactions.
5 OVF Overflow The overflow bit is set to a 1 by the UBM to indicate a buffer overflow condition has
occurred. This bit is used for diagnostic purposes only and is not used for normal
operation. This bit can only be cleared to a 0 by the MCU.
4:0 BPS(4:0) Bytes per sample The bytes per sample bits are used to define the number of bytes per isochronous
data sample. In other words, the total number of bytes in an entire audio CODEC
frame. For example, a PCM 16-bit stereo audio data sample consists of 4 bytes.
There are two bytes of left channel data and two bytes of right channel data. For a
four channel system using 16-bit data, the total number of bytes would be 8, which
would be the isochronous data sample size.
00h = 1 byte, 01h = 2 bytes, …, 1Fh = 32 bytes
A.4.4 USB In Endpoint Configuration Bytes
This section describes the individual bytes in the USB endpoint configuration blocks for the in endpoints. A set of 8
bytes is used for the control and operation of each USB in endpoint. In addition to the USB control endpoint, the
TUSB3200 supports up to a total of seven in endpoints.
A.4.4.1 USB In Endpoint – Y Buffer Data Count Byte (IEPDCNTYx)
The USB in endpoint Y buffer data count byte contains the 7-bit value used to specify the amount of data to be
transmitted in a data packet to the host PC. The no acknowledge status bit is also contained in this byte.
Bit 7 6 5 4 3 2 1 0
Mnemonic NACK DCNTY6 DCNTY5 DCNTY4 DCNTY3 DCNTY2 DCNTY1 DCNTY0
Type R/W R/W R/W R/W R/W R/W R/W R/W
BIT MNEMONIC NAME DESCRIPTION
7 NACK No acknowledge The no acknowledge status bit is set to a 1 by the UBM at the end of a successful
USB in transaction to this endpoint to indicate that the USB endpoint Y buffer is
empty. For control, interrupt, or bulk endpoints, when this bit is set to a 1, all
subsequent transactions to the endpoint will result in a NACK handshake response
to the host PC. Also for control, interrupt, and bulk endpoints, to enable this endpoint
to transmit another data packet to the Host PC, this bit must be cleared to a 0 by the
MCU. For isochronous endpoints, a NACK handshake response to the host PC is
not allowed. Therefore, the UBM ignores this bit in reference to sending the next
data packet. However, the MCU or DMA should clear this bit after writing a data
packet to the buffer.
6:0 DCNTY(6:0) Y Buffer data count The Y buffer data count value is set by the MCU or DMA when a new data packet is
written to the Y buffer for the in endpoint. The 7-bit value is set to the number of bytes
in the data packet for control, interrupt, or bulk endpoint transfers and is set to the
number of samples in the data packet for isochronous endpoint transfers. To
determine the number of samples in the data packet for isochronous transfers, the
bytes per sample value in the configuration byte is used.
