Quantum Time Base

The quantum value for transmitting a pause frame depends on the trigger source for the pause frame.

The quantum value is either zero or takes its value from the GEM Tx_Pause_Quantum register.

• If bit [11] is written with a one, the pause quantum is taken from the Transmit Pause Quantum register. The Transmit Pause Quantum register resets to a value of 0xFFFF giving maximum pause quantum as the default.
• If bit [12] is written with a one, the pause quantum is zero.
• If the tx_pause input is toggled, tx_pfc_sel is Low and the tx_pause_zero input is held Low until the next toggle, the pause quantum is taken from the Transmit Pause Quantum register.
• If the tx_pause input is toggled, tx_pfc_sel is Low and the tx_pause_zero input is held High until the next toggle, the pause quantum is zero.

After transmission, a pause frame transmitted interrupt is generated (bit [14] of the Interrupt Status register) and the only statistics register incremented is the Pause Frames Transmitted register. Pause frames can also be transmitted by the MAC using normal frame transmission methods.