AM3358 mmap bus error

Alexander Hiam

Other Parts Discussed in Thread: SYSCONFIG

Hello all,

I've been working on the BeagleBone, running Angstrom v2011.11-core Linux. I'm writing a Python library (using Python 2.7.2) for peripheral support using the pins broken out on the expansion headers. I'm doing this using the mmap module on /dev/mem, and referring to the AM335x Reference Manual for register addresses. I had no trouble at all with the GPIO registers, and I'm trying to get the ADC working now. The problem I'm having is that I'm getting a bus error when I try to read or write any of the ADC registers.

Here's the output of dmesg after trying to read the ADC CTRL register (absolute address of 0x44e0d040):

[128816.761898] Unhandled fault: external abort on non-linefetch (0x1018) at 0x40785040

I've triple checked my addresses and I'm sure they're correct. Any suggestions would be greatly appreciated.

Thanks in advance,

-Alex

over 13 years ago

0 BrandonAzbell over 13 years ago

TI__Guru 64440 points

Have you taken the ADC out of reset and enabled its clock before attempting to access it?

You would need to check the PRCM (Power and Clock Management) module to enable the ADC first.

0 Alexander Hiam over 13 years ago in reply to BrandonAzbell

Prodigy 25 points

Thanks a bunch Brandon, that seemed to do the trick! For some reason I was thinking the enable bit in the TSC_ADC_SS CTRL register was all that was needed to start the ADC.

-Alex

0 Qmax over 13 years ago in reply to Alexander Hiam

Expert 2280 points

I'm trying to do a similar thing: an user-space application which uses mmap to read and write ADC registers.

It works fine when I read REVISION, SYSCONFIG and IRQ registers, but when I try to to read CTRL or STEPCONFIGx registers I get values which seems random and change every time I read. Is there any restriction on how to access to some of these registers?

Regards, Max

volatile unsigned long *p;
size_t length = 0x1000;    // 4KB page
int prot = PROT_READ | PROT_WRITE;
int flags = MAP_SHARED;
int fd = open("/dev/mem", O_RDWR | O_SYNC);
unsigned int addr;
off_t offset;
int index;

addr = 0x44e0d000 | 0x40; // CTRL register

offset = (off_t)(addr & 0xfffff000);
index = addr & 0xfff;

if (fd < 0) {
    perror("open");
    return 1;
}

p = (unsigned long *)mmap(NULL, length, prot, flags, fd, offset);
if (p == MAP_FAILED) {
    perror("mmap");
    return 4;
}

printf("Read[0x%03x] 0x%08x at address 0x%08x\n", index, p[index], (int)(offset+index));

0 Arturs Elksnis over 12 years ago in reply to BrandonAzbell

Intellectual 715 points

Hi Brandon,

Could you elaborate a little please? Where is PRCM module located? I can't seem to find it in the source.

Thanks

0 Paul Terricciano over 12 years ago in reply to Arturs Elksnis

Intellectual 270 points

Hi Brandon,

I am having the same problem with a SPI driver I am implementing. I have written the CM_PER_SPI1_CLKCTRL register but I am not sure if there are any other registers I need to update. I can write the MCSPI_CH0CONF and MCSPI_MODULCTRL registers but anytime I touch the MCSPI_SYSSTATUS or MCSPI_SYSCONFIG register I get a non-linefetch fault.

Thank You,

Paul

0 JRJ over 11 years ago

Prodigy 110 points

I get bus error when trying to access GPIO2 via dev/mem. GPIO0 and GPIO1 is fine but not GPIO2 -any ideas?

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AM3358 mmap bus error