ST92163 datasheet(136/224 Pages) STMICROELECTRONICS

136 / 224 page

136/224

ST92163 - USB PERIPHERAL (USB)

USB INTERFACE (Cont’d)

8.3.3.1 DMA transfer

DMA descriptors for each endpoint, located in the

ST9 register file, indicate where the related mem-

ory buffer is located in RAM, how large the allocat-

ed buffer is and how many bytes must be transmit-

ted. When a data transfer takes place, the USB-FS

buffering data loaded in an internal 8 byte long

FIFO buffer, and performing Burst-DMA transfers

as appropriate. Then, if needed, the proper hand-

shake answer is generated or expected, according

to the direction of the transfer. At the end of the

transaction, an interrupt is generated: using status

registers and different interrupt vectors, the micro-

controller can determine which endpoint was

served, which type of transaction took place, if er-

rors occurred (bit stuffing, format, CRC, protocol,

missing ACK, over/underrun, etc...).

8.3.3.2 Structure and usage of DMA buffers

Each endpoint has two DMA buffers (one for trans-

mission and the other for reception) whose size

may be up to 1023 bytes each. They can be

placed anywhere in memory (internally or exter-

nally).

For each endpoint, eight Register File locations

are used:

ADDRn_TH and ADDRn_TL: These registers

point to the starting address of the memory buffer

containing the data to be transmitted by endpoint

at the next IN token addressed to it.

COUNTn_TL and COUNTn_TH: These registers

contain the number of bytes to be transmitted by

endpoint

n at the next IN token addressed to it.

ADDRn_RL and ADDRn_RH: These registers

point to the starting address of the memory buffer

which will contain the data received by endpoint

at the next OUT/SETUP token addressed to it.

COUNTn_RL and COUNTn_RH: These registers

contain the allocated buffer size for endpoint

n re-

ception, setting the maximum number of bytes the

related endpoint can receive with the next OUT/

SETUP transaction.

Other register locations related to unsupported

transfer directions or unused endpoints, are avail-

able to the user. Isochronous endpoints have a

special way of handling DMA buffers.

The relationship between register file locations

and memory buffer areas is depicted in Figure 70.

Each DMA buffer is used starting from the bottom,

either during reception or transmission.

The USB interface never changes the contents of

memory locations adjacent to the DMA memory

buffers; even if a packet bigger than the allocated

buffer length is received (buffer overrun condition)

the data will be copied in memory only up to the

last available location.

ST92163 датащи(PDF) 136 Page - STMicroelectronics

ST92163 датащи(HTML) 136 Page - STMicroelectronics

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

датащи скачать

ссылки URL