PRUSS access to external memory DDR2

Hi,

Please refer to https://github.com/beagleboard/am335x_pru_package/blob/master/am335xPruReferenceGuide.pdf 

constant table entry C31 points to DDR.

Also note that SYSCFG register (see section 11.1.2), Bit4 shall be clear to enable access to OCP master ports for DDR access from PRU-ICSS

Hi,

How much data can the PRUSS core access ?

Base on the constant table, the DDR pointer that allow to change is 16bits, is it mean that PRUSS core can access (2^16) x 256 = 16777216, 16MB data?

Thanks and Regards

Keldy

PRUs are 32 bit architecures... so you can address the full memory range of the SoC.

Regards.

Hi,

I'm sorry that i'm not understand. let say in kernel i map the DDR base as 0x80000000 with DDR offset 0x1000, and i make the C31(constant table) point to 0x80001000,

from this 0x80001000 i only allow to access 256bytes using assembly "LBCO REG1, Cn2, OP(255), IM(124)", to access another 256bytes, i have to increase the pointer to 0x80001100.

from the constant table, the pointer allow to change is in range 0x80nn_nn00, so how i access data bigger than 16MB ?

Thanks and Regards

Keldy

Use LBBO/SBBO with direct pointer in the register?

Hi,

I thought PRU only can access the DDR (global memory) through constant table. can it actually access by instruction LBBO/SBBO ?

let say i do mapping in kernel with DDR base 0x80000000, offset 0x1000, size 5MB = 0x500000, so by using SBBO/LBBO, is it PRU can access memory range from 0x80001000 to 0x80501000 ?

Thanks and Regards

Keldy

Hi,

Yes - you can do this. PRU can access entire 32-bit memory range. Note that for accessing  A8 memory range < 0x8000 - you need to use PMAO (PRU OCP Master Address Offset register- 11.1.10 has more details) as this overlaps with PRU-ICSS internal memory map. 

Hi,

Thanks.

when i do my testing, in kernel space, i use ioremap() to map DDR base 0x80000000 with size 2MB. But the kernel crash once i load the kernel module, is it the location that i want to map already been used by other program ?

Thanks and Regards

Keldy

Hi Keldy,

See kernel driver in .../linux-kernel/drivers/uio/uio_pruss.c which uses a parameter to the driver extram_pool_sz.
 The memory is exclusively allocated in the DMA zone for PRU-ICSS. This parameter can be used to allocate DDR memory which can be accessed safely both from PRU firmware and ARM core.

Hope that helps !!

Rakesh Ranjan