A device’s transmit complete interrupt signals μC/TCP-IP that another transmit packet is available to be transmitted or be queued for transmit by the device.
The figure below shows the relationship between a device’s transmit complete interrupt, its transmit complete ISR handling and μC/TCP-IP’s network interface transmit.
(1) The μC/TCP-IP’s Network Interface Transmit calls NetOS_Dev_TxRdyWait() to wait for a specific network interface device semaphore to become ready and/or available to transmit a packet by waiting (with or without timeout) for the specific network interface’s Device Tx Ready Signal to be signaled.
(2) When a device is ready and/or available to transmit a packet, the device generates an interrupt which calls the device’s BSP-level ISR handler.
(3) The device’s BSP-level ISR handler determines which network interface number the specific device’s interrupt is signaling and then calls NetIF_ISR_Handler() to handle the transmit complete interrupt.
(4) The specific device ISR handlers NetDev_ISR_Handler() calls NetOS_Dev_TxRdySignal() to signal the Device Tx Ready Signal for each packet or descriptor that is now available to transmit by the device.
(5) μC/TCP-IP’s Network Interface Transmit’s call to NetOS_Dev_TxRdyWait() returns since the semaphore is made ready by each available device transmit complete that signals the Device Tx Ready Signal.
(6) The Network Interface Transmit then calls the specific network interface and device transmit handler functions to prepare the packet for transmission by the device.