Apollo 1260 clock rates

[Hewitson]

In the manual it says for 060/50 set CLK jumper to 060, and for 66 set to 040.. Surely this means with a 66mhz crystal, the 060 will only run at 33mhz because it will be halved? Or is there something I'm missing here?

[Zetr0]

@Braddo

the 040 divides the external clock so that 40mhz would be 20mhz, an 060 does not divide it so that 50 mhz would be 50mhz respectively.

the reason the Apollo manual states this is two fold

1. Because the higher the frequency (by 1/2 ) the more voltage you need, now... remember that an 060@50 will draw around 3.5 volts of juice, where as an 060@66 will draw closer to 4.5 volts of juice (according to the manual from freescale)

2. memory timmings and access will be different at different frequencies, any wait states would have to be either reduced or completely removed.


I hope that helps.

[Hewitson]

I'm still confused.. Its only clocked at 33mhz with the 66mhz crystal because the jumper is set to 040. Doesn't this mean its running at half the speed it should? Surely thatd be slower than clocking it at 50mhz with the jumper on 060.

Maybe Apollo supplied 132mhz crystals with the 060/66's?

Also a 060@66 is meant to achieve approx 100 MIPS, yet on the amiga it achieves 51. This contributes to my theory.

[Zetr0]

@Braddo

okay.. I may of confused you so sorry about that.

the mc68040 chip divides the governing clock by half.. so if its rated for 33mhz you would need a 66mhz governing clock on the card.

so essentially every other tick it will shunt data around.

the mc68060 chip does not divide the governing clock, this it will shunt data around on every tick.

the methods on the Amiga to calculate MIPS is flawed and cannot take into fact the extra features of an 060. this does not mean some programs wont.

[alexh]

While I do not know exactly what the jumper does, I am sure it is only to do with how the RAM works, not how fast the CPU runs.

The RAM should run at the same speed as the CPU. With a 50MHz crystal the RAM should run at 25MHz for 040 and 50MHz for 060.

However when you go above 50MHz there is no DRAM (SIMMS) that can operate that high. So by running the RAM slower you can keep the system stable.

With a 66MHz crystal and selecting 040 on that jumper you are making the RAM run at 33MHz.

If you had 50ns (or lower) spec SIMMS then maybe you could try the 060 position.

[alexh]

Why would you ever want to run your RAM at 1/2 the speed of the CPU?

The 060 has a large instruction cache and data cache. When running in tight loops (from cache) it will never access RAM. Running the CPU at more than the RAM can really be an advantage in such situations.

[Hewitson]

If its just for the RAM that explains things.. I was thinking it was for the CPU as well.

Thanks

[alexh]

I am 100% sure.

Take a look at this page

http://amigahardware.mariomisic.de/c...cgi?HARDID=223

This is an 25MHz A3640, never designed to be a 68060 accelerator. Doesnt have any RAM. Look at the crystal. It is 50MHz.

If the jumper on the 1260 divided the clock for the CPU, then why doesnt the A3640 use a 25MHz crystal?

[Hewitson]

Don't quite know what you're getting at there.. It has to use a 50mhz because the 040 divides the clock speed it receives by 2.

[Jope]

Well the key there is what you said yourself. The 040 does the dividing, not any circuitry on the CPU card, thus the ram speed jumper doesn't clock the CPU either, just the RAM.

[alexh]

I think it is the RAM controller rather than the RAM, but I am not 100% versed with DRAM.

[Jope]

Yep.

DRAM doesn't have a "clock input" per se, it is more interested in how long you allow it to settle after you have selected the column and row before reading the data.