Re: Re: [openrisc] WB:RISC Clock Ratios

["zhustudio" <zhustudio@ict.ac.cn>]

Dear Marko Mlinar,

	
====== 2003-06-26 08:04:00 =======

>On Thursday 26 June 2003 02:56, zhustudio wrote:
>> Dear Brian Adams,
>>
>> The WB bus is design from WB REV.B2, so it only support synchronous
>> mode, but not the Advanced Synchronous mode that define in WB REV.B3.
>> so it is only run half or below half of the cpu frequency.
>While or1200 have WB B3 and it is compatible with it, this functionality was 
>not yet developed (It basically has B2 functionality).
>The WB functionality and clock multiplying of RISC are two quite distinct 
>things.

but as it does not support WB B3, it can not run the bus as the cpu frequency, because of synchronous ack signal! So the speed of WB bus is only run half of CPU frequency. 


>
>Regarding the questions below, OR1200_CLKDIV_2_SUPPORTED is intended just for 
>what you are trying to do, and yes clocks must be synchronized. You can be a 
>bit out of phase if your timings allow it.
>
>I think Damjan has to go through the checklist, since I never done this yet.
>
>best regards,
>Marko
>
>> Email: zhustudio@ict.ac.cn
>> Date: 2003-04-19
>>
>> ======= 2003-06-25 11:51:00 =======
>>
>> >Hello All,
>> >
>> >  I have a (hopefully) quick sanity check to ask. For the SOC we are
>> >designing we want to have the ability to run WB:RISC clock ratios of 1:1
>> >or 1:2.  To do this I would have to (?)
>> >
>> >1) Define OR1200_CLKDIV_2_SUPPORTED
>> >2) Drive clmode_i on or1200_top appropriately (we plan to use an
>> >external switch or jumper)
>> >3) Drive iwb_clk_i and dwb_clk_i with either the full or half rate WB
>> >clock (depending on how we set #2)
>> >
>> >  Also, are there restrictions on the 1:2 WB/RISC clock relationships?
>> >ie. Must the WB clock must be EXACTLY 1/2 the RISC clock, and phase
>> >aligned.  We plan to have both, but I was wondering if either was
>> >absolutely necessary.
>> >
>> > I it appears that OR1200_CLKDIV_2_SUPPORTED, OR1200_CLKDIV_4_SUPPORTED
>> >and clmode were added to make it easy to do just what I have proposed,
>> >but I have been wrong before. =)
>> >
>> >Thanks,
>> >Brian
>> >
>> >
>> >
>> >
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>
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