Jordi Guillaumes i Pons Barcelona - Catalunya - Europa El 27/02/2013, a les 16:52, Johnny Billquist <bqt at softjar.se> va escriure: Was that an honest bug? There are some details and tricks around SAV which are not very well documented, and which can cause an unbootable system all on its own... Yes, it was. This is the ultimate reason, found by Mark after an entertaining bug hunting dialog: "The Massbus byte count register was incorrectly presumed to be constant during a complete I/O transfer request (it can change due to DMA activity). Prior to the conversion to use the sim_disk library, the Massbus byte count was only read once. After the code restructuring it was read early in the processing and again later in transfer processing. The subsequent read returned a different value which ultimately caused the problems." The whole thread, including some clumsiness from me is here: https://github.com/simh/simh/issues/30