It isn’t long ago that Robert Keck reported that he’d found the issue in the RL11 core that stopped RT-11 from booting, and now there’s another fix to report on.<\/p>\n\n\n\n
This one was found from the new MINC images that were added to Bitsavers in October – more on that later; this bit of the story is just how a freshly installed RL02 image would work fine on simh but not on PDP2011. <\/p>\n\n\n\n
After some serious debugging, I could narrow the issue down to that there was a mismatch in the cylinder that the software thought the drive should be on, and the value that the logic maintains – in the real hardware, that would be the position of the heads in the drive.<\/p>\n\n\n\n
First I thought that the cause might be an over- or underflow of the drive position; the old logic would just wrap around if you’d tell it to seek down from cylinder 0, and simh had some statements to stop that. But while a fix to that effect did change the behaviour somewhat, it didn’t completely fix the problem.<\/p>\n\n\n\n
A bit later I noticed that the software issued a reset instruction just prior to the problem occurring. That pointed me to the logic that clears the registers in the RL11 controller – and yes, that also included the internal representation of the head position in the drives. So I took that out, and surprise – everything just worked.<\/p>\n\n\n\n
The actual fix that the MINC software needed turned out to be just the ‘reset without clearing head and cylinder’; the ‘over- and under’ fix wasn’t needed. But I left it in for good measure.<\/p>\n\n\n\n
As before, for now I’ll just add the updated source for the RL11 here; a new full release with lots of new stuff should be coming up some time this season. But not just yet, there’s too many things to finish.<\/p>\n\n\n\n
It isn’t long ago that Robert Keck reported that he’d found the issue in the RL11 core that stopped RT-11 from booting, and now there’s another fix to report on. This one was found from the new MINC images that were added to Bitsavers in October – more on that later; this bit of the […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5,6],"tags":[],"class_list":["post-1486","post","type-post","status-publish","format-standard","hentry","category-pdp11","category-update","missing-thumbnail"],"_links":{"self":[{"href":"https:\/\/pdp2011.sytse.net\/wordpress\/wp-json\/wp\/v2\/posts\/1486","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pdp2011.sytse.net\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/pdp2011.sytse.net\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/pdp2011.sytse.net\/wordpress\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/pdp2011.sytse.net\/wordpress\/wp-json\/wp\/v2\/comments?post=1486"}],"version-history":[{"count":1,"href":"https:\/\/pdp2011.sytse.net\/wordpress\/wp-json\/wp\/v2\/posts\/1486\/revisions"}],"predecessor-version":[{"id":1488,"href":"https:\/\/pdp2011.sytse.net\/wordpress\/wp-json\/wp\/v2\/posts\/1486\/revisions\/1488"}],"wp:attachment":[{"href":"https:\/\/pdp2011.sytse.net\/wordpress\/wp-json\/wp\/v2\/media?parent=1486"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/pdp2011.sytse.net\/wordpress\/wp-json\/wp\/v2\/categories?post=1486"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/pdp2011.sytse.net\/wordpress\/wp-json\/wp\/v2\/tags?post=1486"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}