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https://github.com/richardghirst/PiBits.git
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Add option to user space implementation to use PCM rather than PWM
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Richard Hirst
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commit
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@ -53,6 +53,11 @@ delay to take us to the end of that timeslot before the next servo output is
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set high. This way there is only ever one servo output active at a time, which
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helps keep the code simple.
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In the following description it refers to using the PWM peripheral. For the
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user space implementation it can instead use the PCM peripheral, see below
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for details. Using PCM is typically a better option, as the 3.5mm jack also
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uses the PWM peripheral, so ServoBlaster can interfere with sound output.
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The driver works by setting up a linked list of DMA control blocks with the
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last one linked back to the first, so once initialized the DMA controller
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cycles round continuously and the driver does not need to get involved except
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@ -108,6 +113,7 @@ To use this daemon grab the servod.c source and Makefile and:
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$ make servod
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$ sudo ./servod
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Using hardware: PWM
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Number of servos: 8
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Servo cycle time: 20000us
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Pulse width units: 10us
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@ -120,6 +126,14 @@ If you want to stop servod, the easiest way is to run:
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$ sudo killall servod
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Note that use of PWM will interfere with 3.5mm jack audio output. Instead
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of using the PWM hardware, you can use the PCM hardware, which is less likely
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to cause a conflict. Please be aware that the PCM mode is very lightly tested
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at present. To use PCM mode, invoke servod as follows:
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$ sudo ./servod --pcm
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Using hardware: PCM
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...
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Features not currently supported in the user space implementation:
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@ -162,6 +176,10 @@ on the wiki (http://elinux.org/RPi_Kernel_Compilation) to compile the kernel,
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then edit the servoblaster Makefile to point at your kernel tree, then build
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servoblaster.
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It is not currently possible to make the kernel implementation use the PCM
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hardware rather than the PWM hardware, therefore it will interfere with 3.5mm
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jack audio output.
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Some people have requested that a servo output turns off automatically if no
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new pulse width has been requested recently, and I've had two reports of
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servos overheating when driven for long periods of time. To support this
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@ -81,6 +81,8 @@ static uint8_t servo2gpio[] = {
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#define CLK_LEN 0xA8
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#define GPIO_BASE 0x20200000
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#define GPIO_LEN 0x100
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#define PCM_BASE 0x20203000
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#define PCM_LEN 0x24
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#define DMA_NO_WIDE_BURSTS (1<<26)
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#define DMA_WAIT_RESP (1<<3)
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@ -120,6 +122,22 @@ static uint8_t servo2gpio[] = {
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#define PWMDMAC_ENAB (1<<31)
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#define PWMDMAC_THRSHLD ((15<<8)|(15<<0))
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#define PCM_CS_A (0x00/4)
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#define PCM_FIFO_A (0x04/4)
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#define PCM_MODE_A (0x08/4)
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#define PCM_RXC_A (0x0c/4)
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#define PCM_TXC_A (0x10/4)
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#define PCM_DREQ_A (0x14/4)
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#define PCM_INTEN_A (0x18/4)
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#define PCM_INT_STC_A (0x1c/4)
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#define PCM_GRAY (0x20/4)
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#define PCMCLK_CNTL 38
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#define PCMCLK_DIV 39
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#define DELAY_VIA_PWM 0
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#define DELAY_VIA_PCM 1
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typedef struct {
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uint32_t info, src, dst, length,
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stride, next, pad[2];
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@ -140,10 +158,13 @@ page_map_t *page_map;
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static uint8_t *virtbase;
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static volatile uint32_t *pwm_reg;
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static volatile uint32_t *pcm_reg;
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static volatile uint32_t *clk_reg;
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static volatile uint32_t *dma_reg;
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static volatile uint32_t *gpio_reg;
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static int delay_hw = DELAY_VIA_PWM;
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static void set_servo(int servo, int width);
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static void
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@ -304,10 +325,15 @@ init_ctrl_data(void)
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{
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struct ctl *ctl = (struct ctl *)virtbase;
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dma_cb_t *cbp = ctl->cb;
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uint32_t phys_pwm_fifo_addr = 0x7e20c000 + 0x18;
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uint32_t phys_fifo_addr;
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uint32_t phys_gpclr0 = 0x7e200000 + 0x28;
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int servo, i;
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if (delay_hw == DELAY_VIA_PWM)
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phys_fifo_addr = (PWM_BASE | 0x7e000000) + 0x18;
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else
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phys_fifo_addr = (PCM_BASE | 0x7e000000) + 0x04;
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memset(ctl->sample, 0, sizeof(ctl->sample));
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for (servo = 0 ; servo < NUM_SERVOS; servo++) {
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for (i = 0; i < SERVO_SAMPLES; i++)
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@ -323,9 +349,12 @@ init_ctrl_data(void)
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cbp->next = mem_virt_to_phys(cbp + 1);
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cbp++;
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// Delay
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cbp->info = DMA_NO_WIDE_BURSTS | DMA_WAIT_RESP | DMA_D_DREQ | DMA_PER_MAP(5);
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if (delay_hw == DELAY_VIA_PWM)
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cbp->info = DMA_NO_WIDE_BURSTS | DMA_WAIT_RESP | DMA_D_DREQ | DMA_PER_MAP(5);
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else
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cbp->info = DMA_NO_WIDE_BURSTS | DMA_WAIT_RESP | DMA_D_DREQ | DMA_PER_MAP(2);
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cbp->src = mem_virt_to_phys(ctl); // Any data will do
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cbp->dst = phys_pwm_fifo_addr;
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cbp->dst = phys_fifo_addr;
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cbp->length = 4;
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cbp->stride = 0;
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cbp->next = mem_virt_to_phys(cbp + 1);
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@ -340,23 +369,45 @@ init_hardware(void)
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{
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struct ctl *ctl = (struct ctl *)virtbase;
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// Initialise PWM
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pwm_reg[PWM_CTL] = 0;
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udelay(10);
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clk_reg[PWMCLK_CNTL] = 0x5A000006; // Source=PLLD (500MHz)
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udelay(100);
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clk_reg[PWMCLK_DIV] = 0x5A000000 | (50<<12); // set pwm div to 50, giving 10MHz
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udelay(100);
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clk_reg[PWMCLK_CNTL] = 0x5A000016; // Source=PLLD and enable
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udelay(100);
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pwm_reg[PWM_RNG1] = SAMPLE_US * 10;
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udelay(10);
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pwm_reg[PWM_DMAC] = PWMDMAC_ENAB | PWMDMAC_THRSHLD;
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udelay(10);
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pwm_reg[PWM_CTL] = PWMCTL_CLRF;
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udelay(10);
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pwm_reg[PWM_CTL] = PWMCTL_USEF1 | PWMCTL_PWEN1;
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udelay(10);
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if (delay_hw == DELAY_VIA_PWM) {
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// Initialise PWM
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pwm_reg[PWM_CTL] = 0;
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udelay(10);
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clk_reg[PWMCLK_CNTL] = 0x5A000006; // Source=PLLD (500MHz)
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udelay(100);
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clk_reg[PWMCLK_DIV] = 0x5A000000 | (50<<12); // set pwm div to 50, giving 10MHz
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udelay(100);
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clk_reg[PWMCLK_CNTL] = 0x5A000016; // Source=PLLD and enable
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udelay(100);
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pwm_reg[PWM_RNG1] = SAMPLE_US * 10;
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udelay(10);
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pwm_reg[PWM_DMAC] = PWMDMAC_ENAB | PWMDMAC_THRSHLD;
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udelay(10);
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pwm_reg[PWM_CTL] = PWMCTL_CLRF;
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udelay(10);
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pwm_reg[PWM_CTL] = PWMCTL_USEF1 | PWMCTL_PWEN1;
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udelay(10);
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} else {
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// Initialise PCM
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pcm_reg[PCM_CS_A] = 1; // Disable Rx+Tx, Enable PCM block
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udelay(100);
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clk_reg[PCMCLK_CNTL] = 0x5A000006; // Source=PLLD (500MHz)
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udelay(100);
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clk_reg[PCMCLK_DIV] = 0x5A000000 | (50<<12); // Set pcm div to 50, giving 10MHz
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udelay(100);
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clk_reg[PCMCLK_CNTL] = 0x5A000016; // Source=PLLD and enable
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udelay(100);
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pcm_reg[PCM_TXC_A] = 0<<31 | 1<<30 | 0<<20 | 0<<16; // 1 channel, 8 bits
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udelay(100);
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pcm_reg[PCM_MODE_A] = (SAMPLE_US * 10 - 1) << 10;
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udelay(100);
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pcm_reg[PCM_CS_A] |= 1<<4 | 1<<3; // Clear FIFOs
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udelay(100);
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pcm_reg[PCM_DREQ_A] = 64<<24 | 64<<8; // DMA Req when one slot is free?
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udelay(100);
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pcm_reg[PCM_CS_A] |= 1<<9; // Enable DMA
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udelay(100);
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}
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// Initialise the DMA
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dma_reg[DMA_CS] = DMA_RESET;
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@ -365,6 +416,10 @@ init_hardware(void)
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dma_reg[DMA_CONBLK_AD] = mem_virt_to_phys(ctl->cb);
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dma_reg[DMA_DEBUG] = 7; // clear debug error flags
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dma_reg[DMA_CS] = 0x10880001; // go, mid priority, wait for outstanding writes
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if (delay_hw == DELAY_VIA_PCM) {
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pcm_reg[PCM_CS_A] |= 1<<2; // Enable Tx
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}
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}
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static void
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@ -402,6 +457,11 @@ main(int argc, char **argv)
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{
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int i;
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// Very crude...
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if (argc == 2 && !strcmp(argv[1], "--pcm"))
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delay_hw = DELAY_VIA_PCM;
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printf("Using hardware: %5s\n", delay_hw == DELAY_VIA_PWM ? "PWM" : "PCM");
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printf("Number of servos: %5d\n", NUM_SERVOS);
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printf("Servo cycle time: %5dus\n", CYCLE_TIME_US);
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printf("Pulse width units: %5dus\n", SAMPLE_US);
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@ -412,6 +472,7 @@ main(int argc, char **argv)
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dma_reg = map_peripheral(DMA_BASE, DMA_LEN);
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pwm_reg = map_peripheral(PWM_BASE, PWM_LEN);
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pcm_reg = map_peripheral(PCM_BASE, PCM_LEN);
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clk_reg = map_peripheral(CLK_BASE, CLK_LEN);
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gpio_reg = map_peripheral(GPIO_BASE, GPIO_LEN);
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