TFTP transfers do not timeout when data rate is below CURLOPT_LOW_SPEED_LIMIT for CURLOPT_LOW_SPEED_TIME.
Looks like Curl_speedcheck() needs to be called in tftp.c:tftp_receive_packet().
Tested by initiating a transfer with curl binary running as tftp client. Then I pulled the ethernet cable to simulate network dis-connectivity. The transfer does not timeout within the timeframe specified by CURLOPT_LOW_SPEED_TIME.
curl 7.32.0 (x86_64-unknown-linux-gnu) libcurl/7.32.0 OpenSSL/1.0.1c zlib/1.2.7 libidn/1.25 librtmp/2.3
Protocols: dict file ftp ftps gopher http https imap imaps ldap ldaps pop3 pop3s rtmp rtsp smtp smtps telnet tftp
Features: Debug TrackMemory IDN IPv6 Largefile NTLM NTLM_WB SSL libz TLS-SRP