TAS1020B datasheet(34/114 Pages) TI

34 / 114 page

2–20

endpoint interrupt. If the MCU wishes to remain autonomous to the DMA process, the MCU must mask off

the MCU endpoint interrupt (by clearing the OEPIE bit in the USB out configuration register OEPCNFx)

before enabling the DMA process.

When the DMA process completes, the DMA channel disables itself and issues a DMA0 or a DMA1 interrupt

to the MCU. Upon receiving the interrupt, the MCU knows that DMABPCT packets have been sent out to

the C-port. The MCU then enables the appropriate endpoint interrupt (if it had been previously masked off).

The process is now complete.

Direct Exchange Mode

This mode offers the highest bandwidth for bulk OUT transactions. The process is almost identical to the software

handshake mode, the only difference being that the Direct Exchange mode, once enabled, runs continuously until

disabled; whereas the Software handshake mode only remains active for the processing of DMABPCT packets. The

Direct Exchange mode is selected by clearing the bit HSKEN in the DMA channel control register (DMACTL0 and

DMACTL1). When the MCU enables the DMA process, after appropriately setting up the endpoint configuration

registers, the C-port configuration registers, and the DMA channel, the DMA process remains active until disabled

by the MCU. While the DMA channel is active, received packets continue to be retrieved from the appropriate endpoint

buffer and transferred to the C-port for transmission to the external device.

2.2.7.3.4 Bulk IN Transaction Using DMA

The TAS1020B does not support BULK IN using the DMA resources.

2.2.7.4 Isochronous Transfers

The TAS1020B supports isochronous data transfers both to and from the host PC. Devices that need to send or

receive data at a constant rate must use the isochronous transfer type rate if the bandwidth of the data exceeds the

USB bandwidth allotted to interrupt type transactions. IN endpoints 1 through 7 and OUT endpoints 1 through 7 can

all be configured as isochronous endpoints.

Isochronous transfers must include the use of a DMA channel; MCU-supported isochronous transfers are not

allowed. Since the TAS1020B has only two DMA channels, at any point in time only two isochronous transactions

can be concurrently supported by the TAS1020B.

To setup an isochronous IN or an isochronous OUT transaction, the MCU must initialize the appropriate IN or OUT

USB endpoint configuration block. For isochronous transactions, this entails programming the buffer size and buffer

base address, enabling the endpoint interrupt, setting the ISO bit (to flag that the endpoint is an isochronous

endpoint), clearing the NACK bit, and enabling the endpoint. When the ISO bit is set, the hardware configures the

buffer to be a single circular buffer (see Section 2.2.7.4.1), using the endpoint buffer size register I/OEPBSIZx and

buffer base address register I/O EPBBAXx. The size of the circular buffer is the size specified in I/OEPSIZx. (This

is not to be confused with the same value in I/OEPSIZx yielding two buffers of that size when the double buffer mode

is selected for control, interrupt, and bulk transactions.)

The TAS1020B DMA engine has two DMA channels. Each channel can be assigned to any IN or OUT endpoint that

has been configured as an isochronous endpoint. (As previously discussed, DMA channels can also be assigned to

bulk out endpoints). If an isochronous OUT endpoint receives data, the DMA channel assigned to the endpoint will

retrieve the data from the endpoint buffer and transfer it to the C-port for outputting to the external device. If a DMA

channel is assigned to an isochronous IN endpoint, the DMA channel transfers external device data received on the

C-port to the IN endpoint buffer.

Each DMA channel can only implement data flow between endpoint buffers and the C-port. The configuration of each

DMA channel includes a 14-bit field that defines which of the up to 14 time slots in the C-port audio frame the DMA

channel supports. Both DMA channels could thus service OUT endpoints, or IN endpoints, with each DMA channel

supporting different time slots in the audio frame.

Each DMA channel also provides a current buffer count register (DMABCNT0/1). For isochronous OUT transactions,

the count in the register represents the number of bytes being transferred from the OUT endpoint buffer to the C-port

TAS1020B Datasheet(PDF) 34 Page - Texas Instruments

TAS1020B Datasheet(HTML) 34 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL