Re: The Motorola 68030

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4 total messages Started by Matt Dillon Fri, 26 Sep 1986 23:36

#1094

Author: Matt Dillon
Date: Fri, 26 Sep 1986 23:36

18 lines
1423 bytes

>From: swalton@well.UUCP (Stephen R. Walton)
>>The bus data transfer rate of the 68030 is 40 Mbytes/sec.
>
>Think about this.  That's a memory access time of 25 nanoseconds, more than
>4 times as fast as the memory we use in our PC's, Macs, Amigas, and Apples.

	100ns access time @ 40 Mbytes/sec (remember: 32 bit data bus).  I
think that the quickest transfer is 64 Mbytes/sec, which would come out to
about 62ns access time.  This means that your rams actually have to be a bit
faster when you take into account bus buffering.  It isn't unreasonable, and
I think you'd be able to (finally) take advantage of dynamic-ram's block-read
ability.

	I especially like the fact that they do MMU address translation in
parallel with checking the cache.  Anybody know what kind of page-table
cache the MMU has?

							-Matt

Re: The Motorola 68030 (mem access time)

#1102

Author: Thomas J. Olson
Date: Mon, 29 Sep 1986 13:44

23 lines
1622 bytes

Matt writes : 

>        100ns access time @ 40 Mbytes/sec (remember: 32 bit data bus).  I 
>think that the quickest transfer is 64 Mbytes/sec, which would come out to
>about 62ns access time.

  I believe that the 64 Mb per sec figure is for a rather bizarre special 
addressing mode, which is designed to take advantage of "ripple mode"
memory devices.  In these devices you present one address, then clock
four times.  Each clock gives you another bit.  
  For the 68030,  the utility is this : you present a paragraph address
(bottom 7 bits zero).  Then you clock four times, loading four thirty-two
bit words into cache.  You have just saved most of the work involved in
your next three memory cycles.  As far as memory access time goes, lots of
ripple mode devices can clock out ripple bits at better than 62.5 ns/bit.
  Somebody who has a real live data sheet, is this right?

--Tom Olson (olson@rochester)


"In *real* machines, the CPU *never* reads memory.  *Cache* reads memory!"
-- Peter Dibble

Re: The Motorola 68030 (mem access time)

#1115

Author: Thomas J. Olson
Date: Mon, 29 Sep 1986 20:32

23 lines
1701 bytes

Matt writes : 

>        100ns access time @ 40 Mbytes/sec (remember: 32 bit data bus).  I 
>think that the quickest transfer is 64 Mbytes/sec, which would come out to
>about 62ns access time.

  I believe that the 64 Mb per sec figure is for a rather bizarre special 
addressing mode, which is designed to take advantage of "ripple mode"
memory devices.  In these devices you present one address, then clock
four times.  Each clock gives you another bit.  
  For the 68030,  the utility is this : you present a paragraph address
(bottom 7 bits zero).  Then you clock four times, loading four thirty-two
bit words into cache.  You have just saved most of the work involved in
your next three memory cycles.  As far as memory access time goes, lots of
ripple mode devices can clock out ripple bits at better than 62.5 ns/bit.
  Somebody who has a real live data sheet, is this right?

--Tom Olson (olson@rochester)


"In *real* machines, the CPU *never* reads memory.  *Cache* reads memory!"
-- Peter Dibble

Re: The Motorola 68030 (mem access time)

#1129

Author: Wolfgang Rupprecht
Date: Thu, 02 Oct 1986 04:32

16 lines
1463 bytes

>  For the 68030,  the utility is this : you present a paragraph address
>(bottom 7 bits zero).  Then you clock four times, loading four thirty-two
>bit words into cache.  You have just saved most of the work involved in
>your next three memory cycles.  As far as memory access time goes, lots of
>ripple mode devices can clock out ripple bits at better than 62.5 ns/bit.
>  Somebody who has a real live data sheet, is this right?

The 'nibble' mode devices (thats the buzz-word for the above type of
transfer) that I've seen *don't* need the bottom n-bits zero-ed. They
will accept any address as the first, and give you the next 3
addresses (modulo-4) next. This is even better, as it allows you to
read the address that you are really interested in first, and do the
prefetches last. 

-- 
Wolfgang Rupprecht	{harvard|decvax!cca|mit-eddie}!lmi-angel!wsr

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