User guide

Details transmitter

 padding

starting with revision 1.7 the GMACII transmitter makes the padding to extend a frame that it meets the

minimum framelength of 64 bytes (for older versions that was business of the software)

example: the TCNT was set to 60 bytes, this tells the transmitter to send 60 bytes from the transmit-

buffer, append the 4 bytes from the automatically generated CRC, and 64bytes are on the line

setting the TCNT to less than 60 Bytes, a frame with TCNT+ 4 Bytes was send !!, but that frame could be

removed from a switch or a networkcard, because of violating the minimum length requirement

With the new feature the transmitter appends X”00” bytes up to byte 60, when the TCNT is shorter than

60, this behavior can not be switched off



The transmit-buffer can be filled in any order with the exact bytes needed

 We have two possibilities to start the transmission

1. Wait until the IFI_GMACII_TCR_TRANS_MSK is 0, load the TCNT, start the transmission with setting

IFI_GMACII_TCR_TRANS_MSK, the transmit-buffer is switched immediately and is sending, the next transmit-buffer

can be loaded now

2. Load the transmit-buffer, set the IFI_GMACII_TCR_PRETRANS_MSK, that is the prestart for the transmitter, then

wait until this bit is cleared, the transmit starts at the earliest possible time (after the interframe gap) to send, and the

buffer is switched, we can now load the next transmit frame, with this pre-start it is possible to reach the minimum

interframe-gap of 12 bytes

− mixing both versions to start transmission is not recommended