AVR16EB32 datasheet(16/46 Pages) MICROCHIP

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AVR16EB32 Curiosity Nano

On-Board Debugger

User Guide

DS50003605B - 16

• The default baud rate used in this mode is 9600 bps, but if the CDC is already active or

configured, the previously used baud rate still applies

Debugger firmware version 1.21 and later has the following limitations/features:

• The maximum message length will vary depending on the MSC/SCSI layer timeouts on the host

computer and/or operating system. A single SCSI frame of 512 bytes (498 characters of payload)

is ensured, and files up to 4 KB will work on most systems. The transfer will complete on the first

NULL character encountered in the file.

• The baud rate used is always 9600 bps for the default command:

CMD:SEND_UART=

• Do not use the CDC Override mode simultaneously with data transfer over the CDC/terminal.

If a CDC terminal session is active when receiving a file via the CDC Override mode, it will be

suspended for the duration of the operation and resumed once complete.

• Additional commands are supported with explicit baud rates:

CMD:SEND_9600=

CMD:SEND_115200=

CMD:SEND_460800=

USB-Level Framing Considerations

Sending data from the host to the CDC can be done byte-wise or in blocks, chunked into 64-byte

USB frames. Each frame will be queued for transfer to the debugger’s CDC TX pin. Sending a

small amount of data per frame can be inefficient, particularly at low baud rates, as the on-board

debugger buffers frames but not bytes. A maximum of four 64-byte frames can be active at any

time. The on-board debugger will throttle the incoming frames accordingly. Sending full 64-byte

frames containing data is the most efficient method.

When receiving data on the debugger’s CDC RX pin, the on-board debugger will queue up the

incoming bytes into 64-byte frames, which are sent to the USB queue for transmission to the host

when they are full. Incomplete frames are also pushed to the USB queue at approximately 100 ms

intervals, triggered by USB start-of-frame tokens. Up to eight 64-byte frames can be active at any

time.

An overrun will occur if the host (or the software running on it) fails to receive data fast enough.

When this happens, the last-filled buffer frame recycles instead of being sent to the USB queue, and

a complete data frame will be lost. To prevent this occurrence, the user will ensure that the CDC

data pipe is continuously read, or the incoming data rate will be reduced.

Sending Break Characters

The host can send a UART break character to the device using the CDC, which can be useable

for resetting a receiver state-machine or signaling an exception condition from the host to the

application running on the device.

A break character is defined as a sequence of at least 11 zero bits transmitted from the host to the

device.

Not all UART receivers have support for detecting a break, but a correctly-formed break character

usually triggers a framing error on the receiver.

Sending a break character using the debugger's CDC has the following limitations:

• Sending a break must NOT be done simultaneously, as using the CDC Override mode (drag-and-

drop). Both these functions are temporary states and must be used independently.

• Sending a break will cause the data currently being sent to be lost. Be sure to wait a sufficient

amount of time to allow all characters in the transmission buffer to be sent (see above section)

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