Datasheet

 2017 Microchip Technology Inc. DS60001516A-page 779
SAM9G20
5. The Host controller raises the request for the first write transaction. By the time the transaction is completed, a frame boundary is
crossed.
6. After completing the first write transaction, the Host controller skips the second write transaction.
Consequence: When this error occurs, the Host controller tries the same IN token again.
Problem Fix/Workaround
This problem can be avoided if the system guarantees that the status update can be completed within the same frame.
44.1.12.2 UHP: ISO OUT transfers
Conditions:
Consider the following sequence:
1. The Host controller sends an ISO OUT token after fetching 16 bytes of data from the system memory.
2. When the Host controller is sending the ISO OUT data, because of system latencies, remaining bytes of the packet are not avail-
able. This results in a buffer underrun condition.
3. While there is an underrun condition, if the Host controller is in the process of bit-stuffing, it causes the Host controller to hang.
Consequence: After the failure condition, the Host controller stops sending the SOF. This causes the connected device to go into suspend
state.
Problem Fix/Workaround
This problem can be avoided if the system can guarantee that no buffer underrun occurs during the transfer.
44.1.12.3 UHP: Remote Wakeup Event
Conditions:
When a Remote Wakeup event occurs on a downstream port, the OHCI Host controller begins sending resume signaling to the device.
The Host controller is supposed to send this resume signaling for 20 ms. However, if the driver sets the HcControl.HCFS into USBOPER-
ATIONAL state during the resume event, then the Host controller terminates sending the resume signal with an EOP to the device.
Consequence: If the Device does not recognize the resume (< 20 ms) event then the Device remains in suspend state.
Problem Fix/Workaround
Host stack can do a port resume after it sets the HcControl.HCFS to USBOPERATIONAL.
44.1.13 USART
44.1.13.1 USART: TXD Signal is floating in Modem and Hardware Handshaking mode.
TXD signal should be pulled up in Modem and Hardware Handshaking mode.
Problem Fix/Workaround
TXD is multiplexed with PIO which integrates a pull up resistor. This internal pull-up must be enabled.
44.1.13.2 USART: DCD is Active High instead of Low
The DCD signal is active at High level in the USART Modem Mode .
DCD should be active at Low level.
Problem Fix/Workaround
Add an inverter.
44.1.14 Power Management Controller (PMC)
44.1.14.1 PMC: PMC bad frequency after MDIV switching
If MDIV and another field (CSS or PRES) are changed at the same, the clock frequency may not be correct.
Problem Fix/Workaround
For each clock switching, the user must take care to:
• change fields CSS, MDIV, PRES one by one
• wait MCKRDY bit setting in PMC_SR before changing PMC_MCKR
• ensure each transitory frequency value is in operational range for PCK and MCK