What routines use on what routines
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safeprint: 

checksum: safeprint

grabmodem:

send: safeprint

match: safeprint

hangup_modem: send

unlockmodem:

bail_out: hangup_modem unlockmodem

lockmodem: bail_out

getline: bailout safe_print

getpacket: bail_out safeprint

main: lockmodem grabmodem bail_out send match hangup_modem getpacket getline checksum