Usb Transaction - Freescale Semiconductor ColdFire MCF52210 ColdFire MCF52211 ColdFire MCF52212 ColdFire MCF52213 Reference Manual

Universal Serial Bus, OTG Capable Controller
1–0 Reserved, should read as zeroes
Reserved
ADDR[31:0] The Address bits represent the 32 -bit buffer address in system memory. These bits are unchanged by the
USB-FS.
15.3.5

USB Transaction

When the USB-FS transmits or receives data, it computes the BDT address using the address generation
shown in Table 2. After the BDT has been read and if the OWN bit equals 1, the SIE transfers the data via
the DMA to or from the buffer pointed to by the ADDR field of the BD. When the TOKEN is complete,
the USB-FS updates the BDT and change the OWN bit to 0 if KEEP is 0. The STAT register is updated
and the TOK_DNE interrupt is set. When the microprocessor processes the TOK_DNE interrupt it reads
the status register, this gives the microprocessor all the information it needs to process the endpoint. At
this point, the microprocessor allocates a new BD so additional USB data can be transmitted or received
for that endpoint, and process then the last BD. The following figure shows a time line how a typical USB
token would be processed.
USB_RST
Interrupt Generated
USB Host
The USB has two sources for the DMA overrun error. First, the memory latency on the BVCI initiator
interface may be too high and cause the receive FIFO to overflow. This is predominantly a hardware
performance issue, usually caused by transient memory access issues. Second, the packet received may be
larger than the negotiated MaxPacket size. This would be caused by a software bug.
In the first case, the USB responds with a NAK or Bus Timeout (BTO - See bit 4 in
"Error Interrupt Status Register
bit is set in the ERR_STAT register of the core for host and device modes of operation. Depending on the
values of the INT_ENB and ERR_ENB register, the core may assert an interrupt to notify the processor of
the DMA error. In device mode, the BDT is not written back nor is the TOK_DNE interrupt triggered
MCF52211 ColdFire® Integrated Microcontroller Reference Manual, Rev. 2
15-8
Table 15-3. Buffer Descriptor Byte Fields (continued)
USB RST
SETUP TOKEN
IN TOKEN
OUT TOKEN
Function
Figure 15-6. USB Token Transaction
(ERR_STAT)") as appropriate for the class of transaction. The DMA_ERR
SOF
SOF
Interrupt Generated
DATA
DATA
DATA
ACK
TOK_DNE
Interrupt Generated
ACK
TOK_DNE
Interrupt Generated
ACK
TOK_DNE
Interrupt Generated
Section 15.4.1.11,
Freescale Semiconductor