Gregory's Serverseveral issues. this first issue, during a host to device write, holds the arbitration bus too long. it should release immediately after the second arb/gnt pulse
|
100 comments
 @tubetime it’s been so long since this experiment started I forget what you’re trying to do! so i don't know how this flag is getting set. my hack is to preemptively clear the flag right before starting DMA, and so far, it seems to be working. i think this code was "working" with the real ESDI drive because that one uses burst mode DMA and it finishes up very quickly, before the irq14wait routine can exit early.  @tubetime When you find yourself asking, "How did this ever work?" and it turns out the answer is "It didn't." @tubetime I've used that library before, yes it really is easy. You probably won't set any throughput records, but it was great for writing diagnostic logs that were later read back and uploaded. @tubetime What’s the end goal here, boot the laptop using a SD card that’s emulating a Micro Channel hard drive interface, via Teensy? @tubetime I know it’s not the point of your project, but didn’t this laptop have PCMCIA? Would one of these work as a boot drive? Digigear SD SDHC SDXC to PCMCIA PC Card, Adapter Supports, ATA Flash Memory https://a.co/d/agF7LO9 my drive doesn't implement this weird feature called pseudo RBAs--it's a way to artificially limit the maximum possible block address, presumably so they can hide the partition data. i suspect the BIOS checks this, so i'll have to implement it. ugh. that means i need to figure out this incomprehensible diagram.  @tubetime  @tubetime "No command can not access" so.. uh.. commands can access? 🤯  @tubetime Your recent posts make me believe you’re a time traveller - perhaps the great-great-grandson of an IBM engineer who as a child found an old notebook complaining about this problem your grandpa just couldn’t solve and that he was fired for and altered the arc of his life. You studied your whole life as an engineer for this moment to come back to today when the hardware was still available, fix the problem, then go back and help your grandpa. Let us know how it turns out. @amart not too far off! my grandfather worked there. i once reverse engineered a prototype floppy drive he worked on, and got it working again. https://twitter.com/TubeTimeUS/status/1617703291483467776 @tubetime how does that even work? After the first iteration isn't the refresh bit always set, so it's stuck in an infinite loop if it never IRQs? @SteveSyfuhs oh sorry REFRESH_BIT is a macro that grabs an IO port bit that toggles with the DRAM refresh signal every 15us. @tubetime @tubetime I implemented PS/2 DMA in an emulator good enough to get a Sound Blaster working a while ago and god help us all @luigithirty nice, you didn't even have to get burst mode working 😉 |
had a theory and it reproduces in simulation. the transfer request flag isn't getting cleared soon enough. la_dma_selected is what can clear this flag and it is changed on the falling edge of cmd, which is too late to catch the ARB/GNT pulse.