LPC burst accesses

WITTROCK jwittrock at maginst.com
Wed Dec 12 00:43:25 EST 2007

I remember doing something like this a while back.  I ended up not
implementing it in my project for other reasons, but here is some
correspondence I had with Freescale:

The question
I am using the LocalPlus bus and BestComm on a MPC5200B to communicate with
an external FPGA.

I am currently using CS2 as the chip select for the FPGA.  If I configure
the chip select 2 configuration register for a 16bit address width and 2
byte bus width then all works well (MBAR + 0x0308 = 0x00003500).

I am now trying to configure CS2 to operate in LargeFlash mode with 2 byte
bus width and 26bit address (MBAR + 0x0308 = 0x00003D00) in order to support
a burst read.  I have configured the Chip Select Burst Control Register
(BRE2=1), and ensured that PCI is disabled, however I do not see a burst
read performed on the bus.

Before I investigate any further, should it be possible to use the LP in
LargeFlash mode together with its assosciated FIFO and BestComm to perform a
burst read?

The Reply
Local Plus controller performs burst read from LargeFlash or MostGraphic
memory only if an XLB master (CPU) or SCLPC interface initiates burst

In the case of CPU, you should enable cache for Local Plus memory.
In the case of SCLPC, you should define BPT=8 in the SCLPC Control Register
(MBAR + 0x3C08).

Other configurations doesn't force bursting.

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opportunity to serve you.
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I hope its of some use.


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