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zmodem bug 2 ?

Moderator: boris

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Joined: Mon Jun 13, 2016 8:50 am
by Dirk » Sun Aug 28, 2016 3:09 pm
Terraterm zmodem ignores receiver buffer limit.

If I have a look in Chuck Forsberg "The ZMODEM Inter Application File Transfer Protocol"

Chapter 8 (Page 19)
8.2 File Transmission

ZCRCW data subpackets expect a response before the next frame is sent. If the receiver does not indicate overlapped I/O capability with the
CANOVIO bit, or sets a buffer size, the sender uses the ZCRCW to allow the receiver to write its buffer before sending more data.

Chapter 9 (Page 24)
9.5 Segmented Streaming

If the receiver cannot overlap serial and disk I/O, it uses the ZRINIT frame to specify a buffer length which the sender will not overflow. The sending program sends a ZCRCW data subpacket and waits for a ZACK header before sending the next segment of the file.

Attached is a ZMODEM.LOG file.
How we can see in the logfile at line 6, the receiver defines a max. buffer size of 0x400 (1024 byte), but terraterm is sending and sending and ...
Yes terraterm is sending subpackets of ~1024 bytes but does not wait for a ZACK before sending the next segment of the file.



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