Dwayne Dietrich

MCF5208 SplitBus

Discussion created by Dwayne Dietrich Employee on Mar 31, 2006
This message contains an entire topic ported from the WildRice - Coldfire forum.  Freescale has received the approval from the WildRice administrator on seeding the Freescale forum with messages.  The original message and all replies are in this single message. We have seeded this new forum with selected information that we expect will be of value as you search for answers to your questions.  Freescale assumes no responsibility whatsoever with respect to Posted Material.  For additional information, please see the Terms of Use - Message Boards and Community Forums.  Thank You and Enjoy the Forum!


Dec 27, 2005, 5:46 AM
Post #1 of 6 (105 views)
Copy Shortcut
 [ColdFire] MCF5208 SplitBus  Can't Post 
--------------------------------------------------------------------------------
 
Hello all,
I am developping a produced based on Coldfire 5208.
I will use 16 bits only SDRam and Flash Data Bus because low price is
very important for this project and I have a very small PCB to route the
bus.
Does anyone have a comparative benchmark with a Coldfire 52XX in 16 bits
and 32 bits mode ?
Is there an advantage to split the bus ( D[15:0] for SDR SDRAM and
D[31:16] for the flash) or should I rather share D[0:15 between SDRAM
and Flash ? If I use split bus with SDR SDRAM, what should be the value
for DRAMSEL ?
Thanks for your help.
Stan
 
 
 
--------------------------------------------------------------------
Jan 5, 2006, 3:58 AM
Post #2 of 6 (97 views)
Copy Shortcut
 RE: [ColdFire] MCF5208 SplitBus [In reply to]  Can't Post 
--------------------------------------------------------------------------------
 
Hi,
I don't have any benchmark but only basic ideas :
* When you use the split bus feature, in fact you greatly simplify the
routing => it's like if you have 2 data buses :
- one for RAM
- one for flex (extensions plugged on the bus)
=> for EEPROM, LAN controller, IDE controller...
Thus this makes sense only if you need both of them...
Another advantage is that you use a 3V3 device. Thus you only need 2 powers:
* 1V5 : core + PLL
* 3V3 : SD_VDD + EVDD
When routing data bus to SDRAM you can scramble the bits in the LSB and/or
MSB and you can invert LSB/MSB if you do the same for DQS and BE signals
(like in the EVB).
The counterpart plugging SDR-DRAM in 16 bits is that you must to make 2
accesses to RAM to get a 32 bits word => speed divided by 2. But keep in
mind that DRAM is cached with SRAM working at full speed.
So the answer is not so easy. It's more a choice.
Personally, I choosed to use the same structure than in the EVB to make the
tests easier...
PS : there is a mistake in the EVB : they inverted #BS0 and #BS1 signals if
you look accurately.

-----Message d'origine-----
De : De la
part de Stan Marly
Envoyé : mardi 27 décembre 2005 14:46
Objet : [ColdFire] MCF5208 SplitBus
Hello all,
I am developping a produced based on Coldfire 5208.
I will use 16 bits only SDRam and Flash Data Bus because low price is
very important for this project and I have a very small PCB to route the
bus.
Does anyone have a comparative benchmark with a Coldfire 52XX in 16 bits
and 32 bits mode ?
Is there an advantage to split the bus ( D[15:0] for SDR SDRAM and
D[31:16] for the flash) or should I rather share D[0:15 between SDRAM
and Flash ? If I use split bus with SDR SDRAM, what should be the value
for DRAMSEL ?
Thanks for your help.
Stan
 
 
 
--------------------------------------------------------------------
Jan 9, 2006, 1:45 PM
Post #3 of 6 (81 views)
Copy Shortcut
 Re: [Listserv] [ColdFire] MCF5208 SplitBus [In reply to]  Can't Post 
--------------------------------------------------------------------------------
 
Hi Stan,
Split bus is specifically intended to be used when using DDR-SDRAM. The D[31:16] for DDR and D[15:0] for Flash/SRAM and other Chip Select devices.
If you are using SDR-SDRAM, then you do not use the split bus mode.
In non-split bus mode you can have upto 32-bit port size and if you wish to save dollars and only use 16-bit port size SDR_SDRAM and Flash, they will share the same address and data signals. D[31:16] specifically.
Non-split bus mode has DRAMSEL pulled high.
Regards,
David
 
 
Jan 10, 2006, 1:30 PM
Post #4 of 6 (75 views)
Copy Shortcut
 RE: [ColdFire] MCF5208 SplitBus [In reply to]  Can't Post 
--------------------------------------------------------------------------------
 
Hi jmo,
Thanks for your help.
Is it mendatory to use split bus or can I connect both Ram and Flash to D[0:15] and drive D3 high at reset to select 16 bits mode ? This will make the routing easier since I will only have to route 16 wires for data bus ?
Thanks.
Best regards,
Stan
-----Message d'origine-----
De : De la part de jmo
Envoyé : jeudi 5 janvier 2006 13:46
À : Stan Marly
Objet : RE: [ColdFire] MCF5208 SplitBus
Hi,
I don't have any benchmark but only basic ideas :
* When you use the split bus feature, in fact you greatly simplify the routing => it's like if you have 2 data buses :
- one for RAM
- one for flex (extensions plugged on the bus)
=> for EEPROM, LAN controller, IDE controller...
Thus this makes sense only if you need both of them...
Another advantage is that you use a 3V3 device. Thus you only need 2 powers:
* 1V5 : core + PLL
* 3V3 : SD_VDD + EVDD
When routing data bus to SDRAM you can scramble the bits in the LSB and/or MSB and you can invert LSB/MSB if you do the same for DQS and BE signals (like in the EVB).
The counterpart plugging SDR-DRAM in 16 bits is that you must to make 2 accesses to RAM to get a 32 bits word => speed divided by 2. But keep in mind that DRAM is cached with SRAM working at full speed.
So the answer is not so easy. It's more a choice.
Personally, I choosed to use the same structure than in the EVB to make the tests easier...
PS : there is a mistake in the EVB : they inverted #BS0 and #BS1 signals if you look accurately.

-----Message d'origine-----
De : De la part de Stan Marly Envoyé : mardi 27 décembre 2005 14:46 À :  Objet : [ColdFire] MCF5208 SplitBus
Hello all,
I am developping a produced based on Coldfire 5208.
I will use 16 bits only SDRam and Flash Data Bus because low price is very important for this project and I have a very small PCB to route the bus.
Does anyone have a comparative benchmark with a Coldfire 52XX in 16 bits and 32 bits mode ?
Is there an advantage to split the bus ( D[15:0] for SDR SDRAM and D[31:16] for the flash) or should I rather share D[0:15 between SDRAM and Flash ? If I use split bus with SDR SDRAM, what should be the value for DRAMSEL ?
Thanks for your help.
Stan
 
 
 
--------------------------------------------------------------------
Jan 13, 2006, 1:09 AM
Post #5 of 6 (74 views)
Copy Shortcut
 RE: [ColdFire] MCF5208 SplitBus [In reply to]  Can't Post 
--------------------------------------------------------------------------------
 
Hi,
It isn't mandatory to use this feature: it has been made to make life easier
that's all.
But my advice takes this form: try to use this µC in a way as closer as
possible than they did in the EVB.
Reasons:
* Some of the behaviours are unclear (this device is very to new)
* Thus testing your board can become a nightmare without a
comparison point.
When I was at this point (like you are now), I made this choice and changed
my design to reach that.
Regards
-----Message d'origine-----
De : De la
part de Stan Marly
Envoyé : mardi 10 janvier 2006 22:30
Objet : RE: [ColdFire] MCF5208 SplitBus
Hi jmo,
Thanks for your help.
Is it mendatory to use split bus or can I connect both Ram and Flash to
D[0:15] and drive D3 high at reset to select 16 bits mode ? This will make
the routing easier since I will only have to route 16 wires for data bus ?
Thanks.
Best regards,
Stan
-----Message d'origine-----
De : De la
part de jmo
Envoyé : jeudi 5 janvier 2006 13:46
À : Stan Marly
Objet : RE: [ColdFire] MCF5208 SplitBus
Hi,
I don't have any benchmark but only basic ideas :
* When you use the split bus feature, in fact you greatly simplify the
routing => it's like if you have 2 data buses :
- one for RAM
- one for flex (extensions plugged on the bus)
=> for EEPROM, LAN controller, IDE controller...
Thus this makes sense only if you need both of them...
Another advantage is that you use a 3V3 device. Thus you only need 2 powers:
* 1V5 : core + PLL
* 3V3 : SD_VDD + EVDD
When routing data bus to SDRAM you can scramble the bits in the LSB and/or
MSB and you can invert LSB/MSB if you do the same for DQS and BE signals
(like in the EVB).
The counterpart plugging SDR-DRAM in 16 bits is that you must to make 2
accesses to RAM to get a 32 bits word => speed divided by 2. But keep in
mind that DRAM is cached with SRAM working at full speed.
So the answer is not so easy. It's more a choice.
Personally, I choosed to use the same structure than in the EVB to make the
tests easier...
PS : there is a mistake in the EVB : they inverted #BS0 and #BS1 signals if
you look accurately.

-----Message d'origine-----
De : De la
part de Stan Marly Envoyé : mardi 27 décembre 2005 14:46 À :
Objet : [ColdFire] MCF5208 SplitBus
Hello all,
I am developping a produced based on Coldfire 5208.
I will use 16 bits only SDRam and Flash Data Bus because low price is very
important for this project and I have a very small PCB to route the bus.
Does anyone have a comparative benchmark with a Coldfire 52XX in 16 bits and
32 bits mode ?
Is there an advantage to split the bus ( D[15:0] for SDR SDRAM and D[31:16]
for the flash) or should I rather share D[0:15 between SDRAM and Flash ? If
I use split bus with SDR SDRAM, what should be the value for DRAMSEL ?
Thanks for your help.
Stan
 
 
 
--------------------------------------------------------------------
Jan 19, 2006, 4:20 PM
Post #6 of 6 (65 views)
Copy Shortcut
 [ColdFire] MCF5208 Heads up.... [In reply to]  Can't Post 
--------------------------------------------------------------------------------
 
I found my 5208 bug today.
As always it was my problem, but it was subtle.
The 5282 and 5270 have interrupt controllers with
registers called icrn with in the interrupt controller subsystem
The 5208 also has the same registers in the same subsystem...
Both sets of registers are the same size, 8 bits.
Alas the bit positions are different between the devices.
The end result was that my Ethernet interrupt was setup as nonmaskable,
and if it occurred in exactly the wrong place (when it was supposed
to be masked off)
it corrupted the RTOS logic.
This took me forever to find, so I hope I can save someone porting to
the 5208 some grief.
Paul
 
 
 

Message Edited by Dietrich on 04-01-2006 11:36 AM

Message Edited by Dietrich on 04-04-2006 09:34 PM

Outcomes