RTX with External SDRAM LPC1788 - causes bus fault

Does the evaluation board need some extra logic to access the RAM? Maybe you need to set a jumper somewhere...?

Hello,

Thanks for your reply.

Yes this initialization of the SDRAM works fine when RTX is not involved.

I don't do an exhaustive test of the SDRAM because I've already tested it quite a bit without RTX.

but just to satisfy myself my main does a little test as follows and always passes:

int main (void)
{
    volatile uint32_t *wr_ptr;
    uint32_t data;
    uint32_t i;

    PINSEL_ConfigPin(LED_PORT, RED_LED_PIN, 0);
    PINSEL_ConfigPin(LED_PORT, GRN_LED_PIN, 0);
    GPIO_SetDir(LED_PORT, RED_LED_PIN_MASK, GPIO_DIRECTION_OUTPUT);
    GPIO_SetDir(LED_PORT, GRN_LED_PIN_MASK, GPIO_DIRECTION_OUTPUT);


    wr_ptr = (uint32_t *)0xA0000000;
    for (i = 0; i < 0x100; i++)
    {
        *wr_ptr++ = 0x12345678;
        //*wr_ptr++ = i;
    }

    /* Verifying */
    wr_ptr = (uint32_t *)0xA0000000;
    for (i = 0; i < 0x100; i++)
    {
        data = *wr_ptr;
        //if (data != i)
        if (data != 0x12345678)
        {
            while(1);
        }
        wr_ptr++;
    }

    os_sys_init(init);                        /* Initialize RTX and start init */

    while ( 1 );
}

Any other ideas suggestions would be most appreciated.

Mac

Hello,

Thanks. I implemented the test as shown on that web page. It passes the test but still faults as os_sys_init.

However, that lead me to try reducing the EMC speed (from 120MHz to 60MHz) and it was ok.

So yes this is a memory issue it looks like. If the test passes what else can I try to see what is going wrong as I would really like to run at 120 MHz.

Thanks

M

I should have advised you to do so earlier - interestingly enough, I posted a bootloader from a LPC2478 to a LPC1788 lately, and I have the very same problem! Had to run the EMC clock at 60MHz. I assumed then it was a routing issue, but NXP themselves gave up conflicting statements about the maximum clock speed of the chip...

Just an update.

I got it running at 96MHz and it seems alright.
I also spoke with someone at NXP and they said it should run at 120?

Maybe it is a layout issue on the EA dev board or something along these lines.

Cheers.

Mac

Ok so another update on this topic.

I contacted NXP support and they told me something different than the FAE.

Here is support's response:

"Thank you for contacting NXP Semiconductors.
The EMC in the LPC177x/8x family can run at a maximum speed of 80 MHz (see the Tcy(clk) = 12.5ns minimum in the data sheet).
You should divide the clock down using the EMCCLKSEL registers."

I guess I missed that in the datasheet.

Hope this is of use to someone else.

Regards,

M

Now it's 80 MHz?
Time to make up your minds NXP :-)

I believe this is incorrect. The data sheet (Table 15. Dynamic characteristics: Static external memory interface, page 81) is referring to a static external memory.

The tables after this (Table 16-18. Dynamic characteristics: Dynamic external memory interface, page 83 - page85) are the ones that pertain to running a SDRAM.

I believe this clock, called the EMC_CLK, is a function of the ouptut from the PLL, and the EMC_CLOCK_DIVIDER, as shown in the user's manual on page 35, Fig. 7.

According to Section 4.6.3 on page 51 of the user's manual, this clock can be the same as the CPU clock, and the CPU clock can be 120Mhz, so this clock can be also.

I personally have driven my EMC clock at 108Mhz without and problems from my EMC or the SDRAM (MT48LC2M32B2).

I did experience a problem running it at 120Mhz, but I attributed this to a poor PCB layout.

I hope this helps,

-Dave

Good observation.
I too was able to run at slightly higher rates than 80MHz but I think this is actually the "official" limit for the EMC (static and/or dynamic).
The "clock cycle time" is more directly related to dynamic memory than static so maybe this is just in the wrong spot in the datasheet?

Also, in our target product we have static mem as well so that pretty much decides that.

Thanks.

M

After reading your response, I decided to play around with the values used to program the EMC, and now I am able to get my SDRAM to work at 120Mhz.

Here are my results:

...clearing SDRAM (8388608 bytes)...............complete! (92 ms.)
...testing SDRAM 16-bit write (2097152 words)...complete! (154 ms.)
...testing SDRAM 16-bit read (2097152 words)....complete! (310 ms.), Errors: 0
...testing SDRAM 32-bit write (1048576 dwords)..complete! (87 ms.)
...testing SDRAM 32-bit read (1048576 dwords)...complete! (148 ms.), Errors: 0

You are welcome to try it for yourself. Here are the values I used:

LPC_SC->EMCCLKSEL = 0x00000000;  // EMC uses a clock rate equal to CPU clock rate...
LPC_SC->CLKOUTCFG = 0x00000100;  // enables clock, sets clock source as CPU clk / 1...
CAS_Latency = 2;
RAS_Latency = 2;
DelayConstant = 0x00000A05;
.
.
.
LPC_SC->EMCDLYCTL   = DelayConstant;

I still believe the time entry in the datasheet is specific to the table that it is listed in, namely static memory. It is referenced throughout that table in other timing parameters, but no where else in the data sheet.

I put in another tech support request to NXP for clarification on this subject, and referenced this forum thread for them...

Good luck,

Dave

Dave,

Please post any NXP response here. Thank you.