From 474ad076c3b88598a2cfca3d781deced5ee8593a Mon Sep 17 00:00:00 2001
From: David Schmenk <dschmenk@astropi.att.net>
Date: Thu, 20 Jun 2013 09:32:51 -0700
Subject: [PATCH] Add serial clock signal from GPIO 4 (header pin # 7)

---
 src/a2serclk.c | 96 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 96 insertions(+)
 create mode 100644 src/a2serclk.c

diff --git a/src/a2serclk.c b/src/a2serclk.c
new file mode 100644
index 0000000..d548a8c
--- /dev/null
+++ b/src/a2serclk.c
@@ -0,0 +1,96 @@
+//
+// Modified from:
+//  How to access GPIO registers from C-code on the Raspberry-Pi
+//  Example program
+//  15-January-2012
+//  Dom and Gert
+//  Revised: 15-Feb-2013
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+// Access from ARM Running Linux
+#define BCM2708_PERI_BASE        0x7E000000
+#define ARM_PERI_BASE            0x20000000
+#define GPIO_OFFSET              0x00200000
+#define CMGP_OFFSET              0x00101000
+#define GPIO_BASE                (ARM_PERI_BASE+GPIO_OFFSET) /* GPIO controller */
+#define CMGP_BASE                (ARM_PERI_BASE+CMGP_OFFSET) /* CM controller */
+
+// GPIO setup macros. Always use INP_GPIO(x) before using OUT_GPIO(x) or SET_GPIO_ALT(x,y)
+#define INP_GPIO(g) *(gpio+((g)/10)) &= ~(7<<(((g)%10)*3))
+#define OUT_GPIO(g) *(gpio+((g)/10)) |=  (1<<(((g)%10)*3))
+#define SET_GPIO_ALT(g,a) *(gpio+(((g)/10))) |= (((a)<=3?(a)+4:(a)==4?3:2)<<(((g)%10)*3))
+
+#define GPIO_REG(reg) (gpio[(reg-(BCM2708_PERI_BASE+GPIO_OFFSET))/4])
+#define CMGP_REG(reg) (cmgp[(reg-(BCM2708_PERI_BASE+CMGP_OFFSET))/4])
+
+#define GPFSEL0 (0x7E200000)
+#define CM_GP0CTL (0x7E101070)
+#define CM_GP0DIV (0x7E101074)
+
+//
+// Set up a memory regions to access GPIO
+//
+volatile unsigned int *setup_io(reg_base)
+{
+    int  mem_fd;
+    void *io_map;
+
+    // open /dev/mem
+    if ((mem_fd = open("/dev/mem", O_RDWR|O_SYNC) ) < 0)
+    {
+	printf("can't open /dev/mem \n");
+	exit(-1);
+    }
+    // mmap IO
+    io_map = mmap(NULL,             //Any adddress in our space will do
+		  4096,             //Map length
+		  PROT_READ|PROT_WRITE,// Enable reading & writting to mapped memory
+		  MAP_SHARED,       //Shared with other processes
+		  mem_fd,           //File to map
+		  reg_base);        //Offset to peripheral
+    close(mem_fd); //No need to keep mem_fd open after mmap
+    if (io_map == MAP_FAILED)
+    {
+	printf("mmap error %d\n", (int)io_map);//errno also set!
+	exit(-1);
+    }
+    return (volatile unsigned *)io_map;
+ }
+
+// I/O access
+volatile unsigned *gpio, *cmgp;
+
+int main(int argc, char **argv)
+{
+    int g,rep;
+
+    // Set up gpi pointer for direct register access
+    cmgp = setup_io(ARM_PERI_BASE + CMGP_OFFSET);
+    gpio = setup_io(ARM_PERI_BASE + GPIO_OFFSET);
+
+    // Set Clock Manager to provivede ~1.8432 MHz from 500 MHz source (PLLD)
+    CMGP_REG(CM_GP0CTL) = (0x5A << 24) // Password
+	                               // Disable
+	                | (1);         // Src = oscillator
+    usleep(1000);
+    CMGP_REG(CM_GP0CTL) = (0x5A << 24) // Password
+	                               // Disable
+	                | (6);         // Src = PLLD
+    CMGP_REG(CM_GP0DIV) = (0x5A << 24) // Password
+                        | (271 << 12); // IDIV
+    usleep(1000);
+    CMGP_REG(CM_GP0CTL) = (0x5A << 24) // Password
+	                | (1 << 4)     // Enable
+	                | (6);         // Src = PLLD
+    usleep(1000);
+    // Set GCLK function (ALT0) for GPIO 4 (header pin #7)
+    INP_GPIO(4);
+    SET_GPIO_ALT(4, 0x00);
+
+    return 0;
+}
+