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RE: Reading an entire cacheline

To: <>
Subject: RE: Reading an entire cacheline
From: "Kim, Jong-Sung" <>
Date: Mon, 24 Apr 2006 16:23:58 +0900
In-reply-to: <058801c66280$3fa1ebb0$f3479696@LGE.NET>
Original-recipient: rfc822;
Thread-index: AcZigD+A+CMHDL7jSviP63YyQN7LKwE4sZxQ
Hi all,

Was my question too brief? I'm using MIPS5Kf core included in a Broadcom
implemented processor and it has a 32kB d-cache and a same sized i-cache.
Cache configuration is 2-way, 32-byte cacheline for both d- and i-cache
without L2 cache. Of course, MIPS-port Linux as the kernel for it. And, a
onboard block device has problem in its operation. I don't think it's a
kernel problem. So I wanna inspect the contents of cache RAMs at the device
driver's context. I've added some lines of codes look like follow:

        __asm__ __volatile__(
                ".set   noreorder\n\t"
                ".set   mips3\n\t"
                "cache  5, 0x00(%3)\n\t"        // load d-cache tag
                ".set   mips0\n\t"              // by index
                ".set   mips32\n\t"
                "mfc0   %0, $28, 0\n\t"
                "mfc0   %1, $28, 1\n\t"
                "mfc0   %2, $29, 1\n\t"
                .set    mips0\n\t"
                .set    reorder"
                : "=r" (tag), "=r" (data_lo), "=r" (data_hi)
                : "r" (0x80000000 | (way << 14) | (index << 5) | (word <<

This is executed for every index, every way, and every word. The thing aches
my head is the tags from a single cacheline differs. (very often for
d-cache) So I modified the code to reread the cacheline from the first word
when the tag was modified before reading all four words. Then the code never
return. I couldn't find any related information from manual.

Please give me a hint for reading whole cacheline safely.

-----Original Message-----
[] On Behalf Of Kim, Jong-Sung
Sent: Tuesday, April 18, 2006 9:37 AM
Subject: Reading an entire cacheline


Is there any way to read an entire cacheline from the MIPS5Kf? Four
sequential cache instructions do similarly, but sometimes the tags from a
same cacheline differ. How can I read a consistent cacheline safely?


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