TUSB5052 datasheet(67/84 Pages) TI

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8–7

8.4

Host IN/OUT Transaction From/To P-Port

8.4.1

Host IN Transaction

Figure 8–2 illustrates the data flow for a USB IN transaction (from P-port to host) using the DMA transfer.

The MCU sets the IEDB (input-EDB) with the proper parameters (start-address, byte-count, etc.). In addi-

tion, the MCU sets the DMA and P-port transfer direction. Once initialization has completed, MCU starts

the DMA transfer by setting EN = 1 (DMA is in continuous mode). Initially, the UBM NAKs the host be-

cause the buffer is empty (NAK = 1). Once the DMA completes the 64-byte transfer to the X-Buffer, it up-

dates the byte-count (and sets NAK = 0) in IEDB and switches to the Y-buffer (DMA controls the X/Y-bit).

The UBM starts transmitting the X-Buffer to host and the DMA transfers data from the parallel port to the

Y-Buffer. When the UBM completes the transfer, it sets NAK = 1 indicating to the DMA that the buffer is

ready. This ping-pong transfer continues until the MCU halts the transfer (or times out). If for any reason

the DMA does not transfer a full 64-bytes, it updates the (partial) byte-count value (and sets NAK = 0) in

IEDB, and interrupts the MCU. The UBM uses this count to transfer a partial packet to host. Note: the

DMA increments the byte-count and save it in IEDB at the end of the transfer. On the other hand, the

UBM uses the byte-count from IEDB as the transfer count but does not update the IEDB at the end of the

transfer, i.e., the DMA both increments and updates; the UBM only decrements.

UBM

64 Byte

Y-Buffer

64 Byte

X-Buffer

DMA5

DIR = 1

PPDAT

Host

P-Port

UBM uses the X/Y-bit to

select X/Y-buffers. UBM uses the

byte count in IEDB for the IN

transfer. At the end of transfer

UBM sets NAK = 1

DMA sets the X/Y-bit. At the end of

transfer, DMA updates the IEDB

with the byte count (and NAK = 0)

and toggles the X/Y–bit.

Figure 8–2. USB IN Transaction From P-Port (DMA CNT mode)

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