On Fri, 12 Dec 2014 03:58:56 -0800, JeGy wrote:> On Friday, December 12, 2014 10:00:48 AM UTC+1, Boudewijn Dijkstra > wrote: >> Op Fri, 12 Dec 2014 08:32:20 +0100 schreef Jens Gydesen >> <jegy@get2net.dk>: >> > I have a lpc2478 PCB, with 16M SDRAM, 1/4 VGA LCD i. a. This board >> > has run perfect for years. >> > The SDRAM is 2x Micron MT48LC16M4A2. >> > >> > In order to modernize this PCB, the cpu is replaced with the >> > compatible LPC1788. >> > >> > I have problems with the SDRAM, it fails. The program crashes due to >> > read/write errors and the LCD shows distorted displays. >> >> Are you running the CPU and EMC at the same frequency as with the >> LPC2478? And is the trace length the same between the two boards? It >> sounds like your EMC clock signal is unstable or skewed. Try a lower >> frequency first, then go up and tweak the settings (particularly >> EMCDELAY to compensate skewing at high frequencies). >> >> > Does anyone here have expirencies with similar problems ? >> >> Yes. For a customer who wanted maximum performance I wrote an SDRAM >> test function that writes&compares RNG values in display memory at >> different settings and then prints out the number of verify errors per >> run. Also we used a heat gun because errors go up with temperature. >> >> > Do you have a code snip for initializing the SD-controller and >> > SDRAM, so I can compare to my own? >> >> None that I can give you, sorry. >> >> >> >> >> -- >> (Remove the obvious prefix to reply privately.) >> Gemaakt met Opera's e-mailprogramma: http://www.opera.com/mail/ > > Hi, > > Thanks for your answer! > > Sorry for the post of the original > > > The PCB's are the same, just the cpu is replaced. > > I have tried to run the lpc1788 PBC at lower frequency, this makes no > differnce. > > Further i have tried to vary the frequency on the LPC2478 PCB, and this > works, nomatter what i doI know nothing of that specific processor, but I'm assuming that it lets you set up the interface to the RAM in a wide variety of ways, many of which are guaranteed to be wrong. If you're using the same code, go over the interface timing with a fine- toothed comb to make sure that the new processor isn't interpreting something differently. The last time I did this was the Motorola MPC860 (or something -- it was their Power QWICC). That thing almost had another processor between the core and the memory interface pins -- you basically wrote a script in a descriptor that told it how to talk to the DRAM. It was hugely flexible, but that just meant that you had a bazzilion different ways to screw it up and only a few ways to make it work right. I'd also look at the signal timings on the board, if I could do it without loading the traces down too much. At best you'll be able to plug into it with a logic analyzer, but even hanging an O-scope lead on the clock and then probing each wire in turn to see what happens should tell you something. (Of course, it may just tell you that as soon as you start probing it everything goes to hell or suddenly fixes itself -- but that's information, right?) -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Replacing LPC2478 with LPC1788
Started by ●December 12, 2014
Reply by ●December 12, 20142014-12-12
Reply by ●December 12, 20142014-12-12