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THD7/TMD700/TS2000

When using THD7 there are some special things you'll need to know. We will elaborate on this in this section.

In case of the THD7/TMD700/TS2000, AX25_MAC switches the TNC to KISS mode. Everything written about KISS applies to the THD7 setting too, but the THD7 doesn't know about SMACK and RMNC-CRC-KISS, so AX25_MAC will not try to use that. When switching the THD7/TMD700/TS2000 to KISS it will also switch the on-air baudrate to 9600 baud if that was specified with the -B flag. Default speed on air is 1200 Baud (serial line speed is fixed to 9600 baud for the THD7 setting).

Special for the THD7 is to go easy on the TNC. It is very easy to overrun the TNC, after which is stops receiving and transmitting. So when there are multiple packets to send, the driver will insert some time between the packets to give the THD7 a chance to send them. This reduces the number of TNC hangups a lot.

Secondly there is a build-in detection mechanism that watches if the driver still receives data after a transmission. When there is no reception then the THD7 TNC is switched off and on (there is a way to do that, even when the TNC itself does not respond). AX25_MAC then switches the TNC to KISS and communication should be restored.

The driver cannot detect if there is no RX data because the TNC stopped or that there is just no data, so sometimes the TNC may be restarted when it was not needed. I tried to minimize this, but it cannot be avoided. It only occurs when there is not much data anyway so hopefully not too many packets are lost the few seconds it takes to restart the TNC. At least is works reasonably well this way.

The mechanism described above also works for the TMD700 and TS2000. I don't know if these devices need that too, but this way the communication is also recovered when the TMD700 and TS2000 are powered off and on.

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