TUSB5052 datasheet(68/84 Pages) TI

68 / 84 page

8–8

8.4.2

Host OUT Transaction

Figure 8–3 illustrates the data flow for a USB OUT transaction (from host to P-port), using the DMA transfer (DMA

in continues mode). The MCU sets the OEDB (Output-EDB) with the proper parameters (start-address, byte-count,

etc.). In addition, the MCU sets the DMA and P-port transfer direction. Once initialization completes, the MCU clears

the NAK bit to 0 (in OEDB-X) which starts the UBM data transfer from host to X-buffer. Once the X-buffer is full, the

UBM updates OEDB-X, sets NAK = 1, and notifies the DMA. The DMA toggles the X/Y-bit. UBM starts the transfer

from the host to the Y-buffer (X/Y-bit points to Y) and the DMA transfers from the X-buffer to P-port. The ping-pong

transfer continues until the MCU (or an error) halts the transfer. If the UBM does not transfer a full 64-bytes, it updates

the byte-count value (and sets NAK = 1) in OEDB to reflect the partial buffer size. The DMA uses this count to transfer

a partial packet to P-port and interrupt the MCU. Note that the UBM increments the byte-count and saves it in OEDB

at the end of the transfer. On the other hand, the DMA uses the byte-count from OEDB as the transfer count but does

not update the OEDB at the end of transfer, i.e., the UBM both increments and updates; whereas, the DMA only

decrements.

UBM

64 Byte

Y-Buffer

64 Byte

X-Buffer

DMA5

DIR = 0

PPDAT

Host

P-Port

UBM uses the X/Y-bit to

select X/Y-buffer. At the end of

the OUT transfer, UBM

updates the OEDB with the

byte count (and NAK = 1).

DMA sets the X/Y-bit. At DMA

uses the byte count in OEDB for

the transfer. At the end of

transfer DMA sets NAK = 0.

Figure 8–3. USB OUT Transaction to P-Port

TUSB5052 数据表(PDF) 68 Page - Texas Instruments

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