Datasheet

suspend state by sending a Downstream Resume on the USB bus (CTRLB.RESUME set to 1). In both
cases, when the downstream resume is completed, the CTRLB.SOFE bit is automatically set and the
host enters again the active state.
32.6.3.8 Phase-locked SOFs
To support the Synchronous Endpoints capability, the period of the emitted Start-of-Frame is maintained
while the USB connection is not in the active state. This does not apply for the disconnected/connected/
reset states. It applies for active/idle/suspend/resume states. The period of Start-of-Frame will be 1ms
when the USB connection is in active state and an integer number of milli-seconds across idle/suspend/
resume states.
To ensure the Synchronous Endpoints capability, the GCLK_USB clock must be kept running. If the
GCLK_USB is interrupted, the period of the emitted Start-of-Frame will be erratic.
32.6.3.9 Management of Control Pipes
A control transaction is composed of three stages:
• SETUP
• Data (IN or OUT)
• Status (IN or OUT)
The user has to change the pipe token according to each stage using the Pipe Token field in PCFG
(PCFG.PTOKEN).
For control pipes only, the token is assigned a specific initial data toggle sequence:
• SETUP: Data0
• IN: Data1
• OUT: Data1
32.6.3.10 Management of IN Pipes
IN packets are sent by the USB device controller upon IN request reception from the host. All the
received data from the device to the host will be stored in the bank provided the bank is empty. The pipe
and its descriptor in RAM must be configured.
The host indicates it is able to receive data from the device by clearing the Bank 0/1 Ready bit in
PSTATUS (PSTATUS.BK0/1RDY), which means that the memory for the bank is available for new USB
transfer.
The USB will perform IN requests as long as the pipe is not frozen by the user.
The generation of IN requests starts when the pipe is unfrozen (PSTATUS.PFREEZE is set to zero).
When the current bank is full, the Transmit Complete 0/1 bit in PINTFLAG (PINTFLAG.TRCPT0/1) will be
set and trigger an interrupt if enabled and the PSTATUS.BK0/1RDY bit will be set.
PINTFLAG.TRCPT0/1 must be cleared by software to acknowledge the interrupt. This is done by writing
a one to the PINTFLAG.TRCPT0/1 of the addressed pipe.
The user reads the PCKSIZE.BYTE_COUNT to know how many bytes should be read.
To free the bank the user must read the IN data from the address ADDR in the pipe descriptor and clear
the PKSTATUS.BK0/1RDY bit. When the IN pipe is composed of multiple banks, a successful IN
transaction will switch to the next bank. Another IN request will be performed by the host as long as the
PSTATUS.BK0/1RDY bit for that bank is set. The PINTFLAG.TRCPT0/1 and PSTATUS.BK0/1RDY will be
updated accordingly.
SAM D21 Family
USB – Universal Serial Bus
© 2018 Microchip Technology Inc.
Datasheet Complete
DS40001882D-page 809