Atmel Evaluation Kit AT91SAM9M10-G45-EK AT91SAM9M10-G45-EK Hoja De Datos

 803

SAM9M10 [DATASHEET]

6355F–ATARM–12-Mar-13

Data OUT Transfer for an Endpoint with Two Banks

Bank Management, Example of Three Transactions per Microframe

USB 2.0 supports individual High Speed isochronous endpoints that require data rates up to 192 Mb/s (24 MB/s):
3x1024 data bytes per microframe.

To support such a rate, two or three banks may be used to buffer the three consecutive data packets. The micro-
controller (or the DMA) should be able to empty the banks very rapidly (at least 24 MB/s on average).

NB_TRANS field in UDPHS_EPTCFGx register = Number Of Transactions per Microframe.

If NB_TRANS > 1 then it is High Bandwidth.

Example: 

• If NB_TRANS = 3, the sequence should be either

– MData0 

– MData0/Data1 

Token OUT

ACK

Data OUT 3

Token OUT

Data OUT 2

Token OUT

Data OUT 1

Data OUT 1

Data OUT 2

Data OUT 2

ACK

 Cleared by Firmware

USB Bus
Packets

Virtual RX_BK_RDY
Bank 0

Virtual RX_BK_RDY
Bank 1

Set by Hardware
Data Payload written
in FIFO endpoint bank 1

FIFO (DPR) 
Bank 0

Bank 1

Write by UDPHS Device

Write in progress

Read by Microcontroller

Read by Microcontroller

Set by Hardware,
Data payload written
in FIFO endpoint bank 0

Host sends first data payload

 Microcontroller reads Data 1 in bank 0,
 Host sends second data payload

 Microcontroller reads Data 2 in bank 1,
 Host sends third data payload

Cleared by Firmware

Write by Hardware

FIFO (DPR) 

(UDPHS_EPTSTAx)

Interrupt pending

Interrupt pending

RX_BK_RDY = (virtual bank 0 | virtual bank 1)

Data OUT 1

Data OUT 3

MDATA0

MDATA0

MDATA1

DATA2

DATA2

MDATA1

t = 0

t = 52.5 μs
(40% of 125 μs)

RX_BK_RDY

t = 125 μs

RX_BK_RDY

USB line

Read Bank 3

Read Bank 2

Read Bank 1

Read Bank 1

USB bus
Transactions

Microcontroller FIFO 
(DPR) Access