Does the C28 or C28 DMA have access to SDRAM via EPI?

Matthew Schubert

Can anyone confirm? Previous posts seem to indicate that only the M3 core and uDMA have access to SDRAM via EPI, but the technical reference manual has a whole chapter dedicated to C28 access.

From 19.9:

"The EPI peripheral is a shared resource between master subsystem (M3 and μDMA) and control subsystem (C28x and DMA). All masters can access external devices via EPI simultaneously."

I can't find any information on where SDRAM memory would be mapped for access from the C28 side, however. Is it possible that the C28 core only has access to the EPI itself (address lines, CS lines, etc), and not to the memory when it is in SDRAM mode?

over 8 years ago

0 David M. Alter over 8 years ago

TI__Guru 61235 points

Matt,

I assume you are talking about the F28M35xxxx or F28M36xxxx devices. For the original silicon on these devices (silicon rev. '0'), the C28x (control subsystem) had no access to the EPI. On rev.A and later silicon, that functionality was added. That is probably the source of the confusion.

There are comments about this scattered about the documentation. For example in SPRS825B (F28M36 datasheet), Table 2-8, p.19, it says in a footnote:

(3) The Control Subsystem has no direct access to EPI in silicon revision 0 devices.

Hope this helps.
Regards,
David

0 Matthew Schubert over 8 years ago in reply to David M. Alter

Prodigy 220 points

Hi David,

Yes, the F28M35H52C1 specifically.

I guess your answer leads to my next question - where is the SDRAM mapped in the C28's address space? On the M3 side, there is a driver function that can set the base address to a few different places (0x60000000 or 0x80000000 if I remember correctly), but I'm not sure if the same address is also used on the C28 side.

Matt

0 Vivek Singh over 8 years ago in reply to Matthew Schubert

TI__Guru** 109125 points

Hi Matt,

From C28, only SRAM accesses are supported not SDRAM.

Regards,

Vivek Singh

0 Matthew Schubert over 8 years ago in reply to Vivek Singh

Prodigy 220 points

I'm a bit confused. I understand the C28 has access to the onboard SRAM, but I'm specifically asking about external SDRAM via EPI.

The technical reference manual says the C28 core and DMA have access to the EPI (as confirmed by David). Are you saying that it doesn't have access to the EPI, or it just doesn't have access to the mapped memory when the EPI is in SDRAM mode?

0 Vivek Singh over 8 years ago in reply to Matthew Schubert

TI__Guru** 109125 points

Hi Matt,

Are you saying that it doesn't have access to the EPI, or it just doesn't have access to the mapped memory when the EPI is in SDRAM mode?

C28 and it's DMA has access to EPI but only ASRAM accesses are supported which is Host Bus Mode of EPI. In SDRAM mode of EPI, C28x and C28x DMA accesses are not supported.

Regards,

Vivek Singh

0 Vivek Singh over 8 years ago in reply to Vivek Singh

TI__Guru** 109125 points

Hi Matt,

Let me know if you have any further queries on this topic.

Regards,

Vivek Singh

0 Matthew Schubert over 8 years ago in reply to Vivek Singh

Prodigy 220 points

Nope, no more queries. I've written code to have the M3 core mediate data transfer to and from shared RAM space. It will do for now.

0 Sheldon he over 7 years ago in reply to Vivek Singh

Intellectual 420 points

Hi Vivek Singh

Recently, I have tried using M3 core configure EPI to SDRAM mode to access an extern SDRAM chip. I have fully access of this memory from M3 side. But I can only access the 512KB from the start address 0x00300000 on C28 side. Do you mean that this kind of work is not supported yet?

Thanks

Regards

hhelib

0 Vivek Singh over 7 years ago in reply to Sheldon he

TI__Guru** 109125 points

Hi,

From C28x side, only ASRAM accesses are supported. Though in HW nothing prevents from accessing SDRAM as well but that is something not supported and it'll have the limitation like you mentioned.

Regards,

Vivek Singh

0 Sheldon he over 7 years ago in reply to Vivek Singh

Intellectual 420 points

Hi，
Glad to hear your replay that soon.
Regards,
hhelib

0 Sheldon he over 7 years ago in reply to Vivek Singh

Intellectual 420 points

Hi,
I am also curious about if there are any risk to use the 512KB on C28 side? We want to use this memory to do program field upgrade and maybe used as a shared memory.
Regards
hhelib

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Does the C28 or C28 DMA have access to SDRAM via EPI?