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Re: [lwip-users] LPC1768 lpc_low_level_input: Packet dropped witherrors

From: Paul Webber
Subject: Re: [lwip-users] LPC1768 lpc_low_level_input: Packet dropped witherrors (0xffffffff)
Date: Fri, 28 Nov 2014 20:02:30 +0000

I just finished implimenting 1.41 on the LPC 4078 using parts of the NXP 
examples. The DMA for the MAC works only with the 32K (in the LPC 4078) block. 
I used the linker file to make sure nothing else ended up in that memory block. 
Also if you are using the example provided by NXP there are other things in 
that memory block, descriptors for the DMA and extra buffers.


From: address@hidden <address@hidden> on behalf of Simon Goldschmidt 
Sent: Friday, November 28, 2014 4:03 AM
To: address@hidden
Subject: Re: [lwip-users] LPC1768 lpc_low_level_input: Packet dropped 
witherrors (0xffffffff)

Jan Menzel wrote:
> On 28.11.2014 03:07, Grzegorz Niemirowski wrote:
>> Does your low level driver use DMA? Is AHB-SRAM accessible by DMA?
> Yes, all memory is accessible via DMA. IIRC datasheet says that flash
> can not be used with EMAC.

I don't know the LPC1768, but a quick look at the LPC1769/68/67/66/65/64/63 
Datasheet brings up this:

--- snip ---
On-chip SRAM includes:
-  32/16 kB of SRAM on the CPU with local code/data bus for high-performance 
CPU access.
-  Two/one 16 kB SRAM blocks with separate access paths for higher throughput.
   These SRAM blocks may be used for Ethernet, USB, and DMA memory, as well as
   for general purpose CPU instruction and data storage.
--- snap ---

To me, this implies the first SRAM block is for CPU-only storage (like stack, 
state info, etc) and cannot be used for DMA.


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