So I managed to get it working in kernel space - I'm not entirely sure what
I did to fix it - I did a full read/modify/write on the GPIO registers and
changed the gpio pointer to u8 but that's about it. Works ok at outputting
a 10khz square wave with about a few us latency but doesn't look that much
better than the user-space however I haven't done any load tests yet so
I'm guessing that doesn't say much. Anyhow code is below - feel free to rip
it apart or tell me better ways of doing things.
#include <linux/module.h>
#include <linux/ioport.h>
#include <asm/io.h>
#include <rtdm/rtdm_driver.h>
MODULE_LICENSE("GPL");
#define BCM2708_PERI_BASE_VIRT 0x20000000
#define GPIO_BASE_VIRT (BCM2708_PERI_BASE_VIRT + 0x200000) /* GPIO
controller */
//Offsets of registers
#define GPFSEL0 (0x00) /*GPIO Function Select 0*/
#define GPFSEL1 (0x04) /*GPIO Function Select 1*/
#define GPFSEL2 (0x08) /*GPIO Function Select 2*/
#define GPFSEL3 (0x0C) /*GPIO Function Select 3*/
#define GPFSEL4 (0x10) /*GPIO Function Select 4*/
#define GPFSEL5 (0x14) /*GPIO Function Select 5*/
#define GPSET0 (0x1C) /*GPIO pin Output Set 0*/
#define GPSET1 (0x20) /*GPIO pin Output Set 1*/
#define GPCLR0 (0x28) /*GPIO pin Output Clear 0*/
#define GPCLR1 (0x2C) /*GPIO pin Output Clear 1*/
/*There are any more but these should be enough*/
#define HEARTBEAT_PERIOD 50000 /* 10khz */
static u8 *gpio = NULL;
static rtdm_task_t heartbeat_task;
static int end = 0;
/* NOTE this is all a hack to work on GPIO7 */
void heartbeat(void *cookie)
{
int state = 0;
while (!end) {
rtdm_task_wait_period();
if (state)
iowrite32((1<<7),(gpio+GPSET0));
else
iowrite32((1<<7),(gpio+GPCLR0));
state ^= 1;
}
}
int __init init_heartbeat(void)
{
unsigned int data;
struct resource *mem = NULL;
int err = 0;
mem = request_mem_region(GPIO_BASE_VIRT,0xfff,"gpio");
if (mem == NULL) {
printk("Could not request mem region\n");
err = -ENOMEM;
goto err;
} else {
printk("Have access to mem region\n");
}
gpio = ioremap_nocache(GPIO_BASE_VIRT, 0xfff);
if (gpio == NULL) {
printk("Could not request gpio region\n");
err = -ENOMEM;
goto err;
} else {
printk("Have access to gpio region\n");
}
data = ioread32(gpio+GPFSEL0);
data &= ~(7<<21);
iowrite32(data,(gpio+GPFSEL0));
data = ioread32(gpio+GPFSEL0);
data |= (1<<21);
iowrite32(data,(gpio+GPFSEL0));
data = ioread32(gpio + GPFSEL0);
printk("Should now be high %x\n", data);
//return 0;
return rtdm_task_init(&heartbeat_task, "heartbeat", heartbeat, NULL,
99, HEARTBEAT_PERIOD);
err:
return err;
}
void __exit cleanup_heartbeat(void)
{
end = 1;
rtdm_task_join_nrt(&heartbeat_task, 100);
iounmap(gpio);
printk("Unliading modklskdksdf\n");
release_mem_region(GPIO_BASE_VIRT, 0xfff);
}
module_init(init_heartbeat);
module_exit(cleanup_heartbeat);
On Wed, Apr 17, 2013 at 2:33 PM, Gilles Chanteperdrix <
[email protected]> wrote:
> On 04/17/2013 10:59 PM, Michael Haberler wrote:
>
> > Ross,
> >
> > any reason not to use just userland memory mapped port I/O like with
> this library: http://www.airspayce.com/mikem/bcm2835 ?
> >
> > that worked fine for me with a userland RT thread, no drivers needed
>
>
> It is a bad idea to access GPIO registers in user-space via memory
> mapped I/O: you will not get the mutual exclusion the kernel driver
> gives you.
>
> --
> Gilles.
>
--
Ross Williamson
Research Scientist - Sub-mm Group
California Institute of Technology
626-395-2647 (office)
312-504-3051 (Cell)
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