Killing Bugs

MacPaint on Macintosh System 2.0

ZTerm on System 7.1

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After some bug fixes and various tweaks to my test code, the lwip program I compiled actually loads on System 7.1! It promptly crashes the 128K running some early System version and even crashes on the SE running System 6.0.8. I think this could be because of the -model far option. I can't take a screen-shot because it is not yielding any time to the system software as it runs.
I spent most of the weekend fixing small issues, then transferring the program numerous times to the Macintosh SE using a terminal program. I haven't gotten around to getting the ethernet card working on the SE, or installing a zip drive in the G4.  Huge flash-back to the days of waiting for the modem to download files from a BBS.
The StdCLib from MPW writes stdout and stderr to text files, which works well. Since I haven't set up the UI, I don't have a menu to quit the program, so I have to force-quit it after a while. Unfortunately, the program doesn't actually work correctly even on System 7.1. It looks like it is getting data from the serial port though. Now, the main lwip error I need to get past is: pbuf_alloc: allocated pbuf 0x2FAB00 pbuf_alloc(length=0) == 0x2FAB00 pppos_input[0]: got 35 bytes pppos_input[0]: got 1 bytes pbuf_header: failed as 0xAB12 < 0x2FAB10 (not enough space for new header size) Assertion "pbuf_header failed " failed at line 681 in :lwip-mac:src:netif:ppp:ppp.c pbuf_free(0x2FAB00) pbuf_free: deallocating 0x2FAB00
Nice of lwip to tell me what file and line the failure is on, but I still can't figure it out...