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Frame Relay for Sangoma Cards (C) Sangoma Technologies Inc. 1999,2000,2001 Page 68 of 78
Non-interrupt driven transmissions
1) The I/O base port register is read until bit 1 is set, implying that there is at least one transmit buffer
available for use by the application.
2) An INFORMATION_WRITE command is performed. If the return code from this command is
zero (successful command), a pointer to the Transmit Status Element to be used is passed to the
application in the first four bytes of the mailbox data area.
3) The pointer to the I-frame data area is read from this Transmit Status Element and the data to be
transmitted is written to the adapter as follows:
a) The 8K memory window is set to the physical memory area so as to access the base
address of the transmit data area.
b) The transmit data is written to the adapter until either:
i) all the data has been written
ii) the upper boundary of the current 8K memory segment has been reached
c) If not all the data has been written, then the 8K memory segment access is adjusted and step
b) is repeated.
It is important to note that the transmit buffer is not a rotational buffer and so no buffer wrapping occurs
as per the receive buffer.