![Freescale Semiconductor MCF54455 Reference Manual Download Page 270](http://html1.mh-extra.com/html/freescale-semiconductor/mcf54455/mcf54455_reference-manual_2330541270.webp)
Universal Serial Bus Interface – On-The-Go Module
Freescale Semiconductor
10-63
10.5.3.4.2
Priming Receive Endpoints
Priming receives endpoints identical to priming of transmit endpoints from the point of view of the DCD.
The major difference in the operational model at the device controller is no data movement of the leading
packet data because the data is to be received from the host.
As part of the architecture, the FIFO for the receive endpoints is not partitioned into multiple channels like
the transmit FIFO. Thus, the size of the RX FIFO does not scale with the number of endpoints.
10.5.3.4.3
Interrupt/Bulk Endpoint Operation
The behaviors of the device controller for interrupt and bulk endpoints are identical. All valid IN and OUT
transactions to bulk pipes handshake with a NAK unless the endpoint is primed. After the endpoint is
primed, data delivery commences.
A dTD is retired by the device controller when the packets described in the transfer descriptor are
completed. Each dTD describes N packets to transfer according to the USB variable length transfer
protocol. The formula below and
describe how the device controller computes the number and
length of the packets sent/received by the USB vary according to the total number of bytes and maximum
packet length. See
Section 10.5.2.1.1, “Endpoint Capabilities/Characteristics (Offset = 0x0)
on the ZLT bit.
With zero-length termination (ZLT) cleared:
N = INT(number of bytes/max. packet length) + 1
With zero-length termination (ZLT) set:
N = MAXINT(number of bytes/max. packet length)
NOTE
The MULT field in the dQH must be set to 00 for bulk, interrupt, and control
endpoints.
Table 10-53. Variable Length Transfer Protocol Example (ZLT=0)
Bytes
(dTD)
Max. Packet
Length (dQH)
N
P1
P2
P3
511
256
2
256
255
—
512
256
3
256
256
0
512
512
2
512
0
—
Table 10-54. Variable Length Transfer Protocol Example (ZLT=1)
Bytes
(dTD)
Max. Packet
Length (dQH)
N
P1
P2
P3
511
256
2
256
255
—
512
256
2
256
256
—
512
512
1
512
—
—
Summary of Contents for MCF54455
Page 33: ...xxviii Freescale Semiconductor ...
Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
Page 843: ...Freescale Semiconductor 1 ...
Page 921: ...Revision History A 6 Freescale Semiconductor ...