From: Luke Kenneth Casson Leighton Date: Fri, 7 Dec 2018 16:13:08 +0000 (+0000) Subject: add conversation notes X-Git-Tag: convert-csv-opcode-to-binary~4799 X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=425d18485ff18f97ca00ecc5a3c46eb990136e68;p=libreriscv.git add conversation notes --- diff --git a/3d_gpu/microarchitecture.mdwn b/3d_gpu/microarchitecture.mdwn index 2a1161251..4928444c6 100644 --- a/3d_gpu/microarchitecture.mdwn +++ b/3d_gpu/microarchitecture.mdwn @@ -309,6 +309,31 @@ on the 6600. they're frickin awesome. the 6600 could do multi-issue LD and ST by way of having dedicated registers to LD and ST. X1-X5 were for ST, X6 and X7 for LD. +---- + +i took a shot at explaining this also on comp.arch today, and that +allowed me to identify a problem with the proposed modulo-4 "lanes" +stratification. + +when a result is created in one lane, it may need to be passed to the next +lane. that means that each of the other lanes needs to keep a watchful +eye on when another lane updates the other regfiles (all 3 of them). + +when an incoming update occurs, there may be up to 3 register writes +(that need to be queued?) that need to be broadcast (written) into +reservation stations. + +what i'm not sure of is: can data consistency be preserved, even if +there's a delay? my big concern is that during the time where the data is +broadcast from one lane, the head of the ROB arrives at that instruction +(which is the "commit" condition), it gets committed, then, unfortunately, +the same ROB# gets *reused*. + +now that i think about it, as long as the length of the queue is below +the size of the Reorder Buffer (preferably well below), and as long as +it's guaranteed to be emptied by the time the ROB cycles through the +whole buffer, it *should* be okay. + # References *