Updates to allow tweaking timing via module parameters

ServoBlaster/Makefile

@@ -1,9 +1,11 @@
-KERNEL_TREE := /home/richard/Pi/git/linux
+KERNEL_TREE := /home/richard/github/linux
 
-all:	servoblaster.ko servodemo
+all:	servoblaster.ko
 
 servoblaster.ko:	servoblaster.c servoblaster.h
-	make -C ${KERNEL_TREE} ARCH=arm CROSS_COMPILE=/usr/bin/arm-linux-gnueabi- M=$(PWD) modules
+	@[ -d ${KERNEL_TREE} ] || { echo "Edit Makefile to set KERNEL_TREE to point at your kernel"; exit 1; }
+	@[ -e ${KERNEL_TREE}/Module.symvers ] || { echo "KERNEL_TREE/Module.symvers does not exist, you need to configure and compile your kernel"; exit 1; }
+	make -C ${KERNEL_TREE} ARCH=arm M=$(PWD) modules
 
 servodemo:	servodemo.c servoblaster.h
 	gcc -Wall -g -O2 -o servodemo servodemo.c -Wl,--export-dynamic `pkg-config --cflags gtk+-3.0 gmodule-export-2.0` `pkg-config --libs gtk+-3.0 gmodule-export-2.0`

ServoBlaster/README.txt

@@ -77,6 +77,42 @@ take the 5 volts for it from the header pins on the Pi, but I find that doing
 anything non-trivial with four servos connected pulls the 5 volts down far
 enough to crash the Pi!
 
+If you wish to compile the module yourself, the approach I took was to run
+rpi-update to get the latest kernel from github, then follow the instructions
+on the wiki (http://elinux.org/RPi_Kernel_Compilation) to compile the kernel,
+then edit the servoblaster Makefile to point at your kernel tree, then build
+servoblaster.
+
+NOTE: There is some doubt over how to configure the PWM clock at present.  For
+me the clock is 600KHz, which leads to a tick lenght of 10us.  However at least
+one person has reported that the pulses are out by about a factor of about 8,
+and so are repeated every 2.5ms rather than every 20ms.  To work round this I
+have added two module parameters:
+
+tick_scale defaults to 6, which should be a divisor of 600KHz, which should
+give a tick of 10us.  You set the pulse width in ticks (echo 2=27 >
+/dev/panalyzer to set 27 ticks).
+
+cycle_ticks is the cycle time in ticks, and defaults to 2000 to give 20ms if
+one tick is 10us.  cycle_ticks should be a multiple of 8.  The max pulse width
+you can specify by writing to /dev/servoblaster is (cycle_ticks/8 - 1), so for
+the default parameters it is 249, or 2.49ms.
+
+For example:
+
+sudo insmod ./servoblaster.ko tick_scale=48
+
+should slow it down by a factor of 8 (6*8=48).
+
+If you can't get quite what you want with tick_scale, you can also tweak
+cycle_ticks.
+
+Eventually I might get round to letting you specify how many servo control
+outputs you want, and which outputs to use, via module parameters.
+
+As of August 30th 2012 the servoblaster.ko module is built against a 2.6.27+
+kernel source from github.
+
 
 Richard Hirst <richardghirst@gmail.com>  August 2012
 

ServoBlaster/servoblaster.c

@@ -50,7 +50,7 @@
 #include <mach/platform.h>
 #include <asm/uaccess.h>
 #include <mach/dma.h>
-#include "servoblaster.h"
+//#include "servoblaster.h"
 
 #define GPIO_LEN		0xb4
 #define DMA_LEN			0x24
@@ -139,6 +139,8 @@ static volatile uint32_t *pwm_reg;
 static dev_t devno;
 static struct cdev my_cdev;
 static int my_major;
+static int cycle_ticks = 2000;
+static int tick_scale = 6;
 
 // Wait until we're not processing the given servo (actually wait until
 // we are not processing the low period of the previous servo, or the
@@ -187,7 +189,7 @@ int init_module(void)
 	}
 
 	ctldatabase = __get_free_pages(GFP_KERNEL, 0);
-	printk(KERN_INFO "ServoBlaster: Control page is at 0x%lx\n", ctldatabase);
+	printk(KERN_INFO "ServoBlaster: Control page is at 0x%lx, cycle_ticks %d, tick_scale %d\n", ctldatabase, cycle_ticks, tick_scale);
 	if (ctldatabase == 0) {
 		printk(KERN_WARNING "ServoBlaster: alloc_pages failed\n");
 		cdev_del(&my_cdev);
@@ -234,7 +236,7 @@ int init_module(void)
 		ctl->cb[i].info   = BCM2708_DMA_NO_WIDE_BURSTS | BCM2708_DMA_WAIT_RESP | BCM2708_DMA_D_DREQ | BCM2708_DMA_PER_MAP(5);
 		ctl->cb[i].src    = (uint32_t)(&ctl->pwmdata) & 0x7fffffff;
 		ctl->cb[i].dst    = ((PWM_BASE + PWM_FIFO*4) & 0x00ffffff) | 0x7e000000;
-		ctl->cb[i].length = sizeof(uint32_t) * 100;	// default 1000us high
+		ctl->cb[i].length = sizeof(uint32_t) * 1;	// default 1 tick high
 		ctl->cb[i].stride = 0;
 		ctl->cb[i].next = (uint32_t)(ctl->cb + i + 1) & 0x7fffffff;
 		// Set gpio lo
@@ -250,7 +252,7 @@ int init_module(void)
 		ctl->cb[i].info   = BCM2708_DMA_NO_WIDE_BURSTS | BCM2708_DMA_WAIT_RESP | BCM2708_DMA_D_DREQ | BCM2708_DMA_PER_MAP(5);
 		ctl->cb[i].src    = (uint32_t)(&ctl->pwmdata) & 0x7fffffff;
 		ctl->cb[i].dst    = ((PWM_BASE + PWM_FIFO*4) & 0x00ffffff) | 0x7e000000;
-		ctl->cb[i].length = sizeof(uint32_t) * 150;	// default 1500us, to give 2.5ms per servo
+		ctl->cb[i].length = sizeof(uint32_t) * (cycle_ticks / 8 - 1);
 		ctl->cb[i].stride = 0;
 		ctl->cb[i].next = (uint32_t)(ctl->cb + i + 1) & 0x7fffffff;
 	}
@@ -262,7 +264,7 @@ int init_module(void)
 	udelay(10);
 	clk_reg[PWMCLK_DIV] = 0x5A000000 | (32<<12);    // set pwm div to 32 (19.2MHz/32 = 600KHz)
 	clk_reg[PWMCLK_CNTL] = 0x5A000011;              // Source=osc and enable
-	pwm_reg[PWM_RNG1] = 6;							// 600KHz/6 = 10us per FIFO write
+	pwm_reg[PWM_RNG1] = tick_scale;							// 600KHz/6 = 10us per FIFO write
 	udelay(10);
 	ctl->pwmdata = 1;								// Give a pulse of one clock width for each fifo write
 	pwm_reg[PWM_DMAC] = PWMDMAC_ENAB | PWMDMAC_THRSHLD;
@@ -346,7 +348,7 @@ static ssize_t dev_write(struct file *filp,const char *buf,size_t count,loff_t *
 		printk(KERN_WARNING "ServoBlaster: Bad servo number %d\n", servo);
 		return -EINVAL;
 	}
-	if (cnt < 0 || cnt > 249) {
+	if (cnt < 0 || cnt > cycle_ticks / 8 - 1) {
 		printk(KERN_WARNING "ServoBlaster: Bad value %d\n", cnt);
 		return -EINVAL;
 	}
@@ -357,7 +359,7 @@ static ssize_t dev_write(struct file *filp,const char *buf,size_t count,loff_t *
 	} else {
 		ctl->cb[servo*4+0].dst = ((GPIO_BASE + GPSET0*4) & 0x00ffffff) | 0x7e000000;
 		ctl->cb[servo*4+1].length = cnt * sizeof(uint32_t);
-		ctl->cb[servo*4+3].length = (250 - cnt) * sizeof(uint32_t);
+		ctl->cb[servo*4+3].length = (cycle_ticks / 8 - cnt) * sizeof(uint32_t);
 	}
 	local_irq_enable();
 
@@ -378,3 +380,9 @@ MODULE_DESCRIPTION("ServoBlaster, Multiple Servo Driver for the RaspberryPi");
 MODULE_AUTHOR("Richard Hirst <richardghirst@gmail.com>");
 MODULE_LICENSE("GPL v2");
 
+module_param(cycle_ticks, int, 0);
+MODULE_PARM_DESC(cycle_ticks, "number of ticks per cycle, max pulse is cycle_ticks/8");
+
+module_param(tick_scale, int, 0);
+MODULE_PARM_DESC(tick_scale, "scale the tick length, 6 should be 10us");
+