byArgh = readb(global_vmemaddr);
if(byArgh==0) printk(KERN_DEBUG "byArgh\n");
writeb (0x5a, global_vmemaddr);
byArgh = readb(global_vmemaddr);
Regards,
Jeff
On Sat, 10 Jul 1999, Klaus Nielsen wrote:
> Aloha guys
>
> I am writing an Ethernet driver for a Internal PCI cable modem with
> some onboard memory that I have mapped using ioremap.
>
> But I have problem reading the memory, more accurately, I can read it
> once, write it many, but not read it a second time.
>
> It is mapped using:
>
> // Remap physical PCI controller LCR memory to virtual memory
> if(((char*)(global_lcr_vmemaddr = (u32) ioremap(global_pci_lcr_memaddr, LCR_MEMORY_RANGE)))==NULL)
> return -EAGAIN;
>
> // Remap physical PCI memory to virtual memory
> if((((char*)global_vmemaddr = (u32) ioremap(global_pci_memaddr,MODEM_MEMORY_RANGE))) == NULL) {
> iounmap((char*)global_lcr_vmemaddr); return -EAGAIN;
> }
>
> The following silly code then works fine:
>
> Byte byArgh;
>
> byArgh = *((Byte*)global_vmemaddr);
> if(byArgh==0) printk(KERN_DEBUG "byArgh\n");
> *((Byte*)global_vmemaddr) = 0x5a;
> byArgh = *((Byte*)global_vmemaddr);
>
> While the PC freezes completely at the last conditional statement
> at the following, almost identical, code fragment:
>
> Byte byArgh;
>
> byArgh = *((Byte*)global_vmemaddr);
> if(byArgh==0) printk(KERN_DEBUG "byArgh\n");
> *((Byte*)global_vmemaddr) = 0x5a;
> byArgh = *((Byte*)global_vmemaddr);
> if(byArgh==0) printk(KERN_DEBUG "byArgh\n"); // DEATH HERE
>
> - as if the bus had not finished the transfer the second time I read.
>
> I have in a similar way mapped PCI LCR memory in the PLX9052 PCI
> controller (that by the way does not support master mode). And I can
> read and write that LCR memory as much as I want.
>
> I have tried changing compiler (to gcc 2.7.2.3), changing the
> modem board with one that works with my WinNT driver, adding
> udelay(60) between accesses, using readb() instead of direct access -
> no change.
>
> If I do _extensive_ memory testing, writing all the memory twice, then
> reading all, writing all again, reading all, writing all again -
> there is no problem reading, but later in the driver when just
> accessing a single byte like in the second example I freeze again.
>
> A small sample code is available at http://www.zorland.dk/jimbo/hw.c
>
> This is my first SW project of any kind on linux, so please be gentle
> with me :-) Maybe I am mapping the memory in a wrong way ?
>
> I am using kernel 2.2.9.
>
> PS: I am in no way acting on behalf of COCOM A/S, this is purely a
> spare time project.
>
> --
> Best regards, Klaus.
> ----------------------------------------------------
> Klaus J. O. Nielsen
> System Engineer, COCOM A/S, www.cocom.dk
> Personal web: http://www.zorland.dk/jimbo
> PGP public key: http://www.zorland.dk/jimbo/kjn.asc
>
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