libbb: library for bit-banging the Ben's uSD port (in progress)

This doesn't work with old kernels, but 2.6.36 should be better. Haven't
tried it yet, though.

libbb/libbb.c

@@ -0,0 +1,126 @@
+/*
+ * libbb/libbb.c - Bitbang library
+ *
+ * Written 2010 by Werner Almesberger
+ * Copyright 2010 Werner Almesberger
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ */
+
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+//#include <sys/wait.h>
+#include <sys/mman.h>
+
+#include "libbb.h"
+
+
+#define	PAGE_SIZE	4096
+
+
+volatile void *libbb_mem;
+
+static int bbd_fd = -1;
+
+
+static int recv_fd(int s)
+{
+	struct msghdr msg;
+	struct cmsg {
+		struct cmsghdr hdr;
+		int fd;
+	} cmsg;
+
+	memset(&msg, 0, sizeof(msg));
+	msg.msg_control = &cmsg;
+	msg.msg_controllen = sizeof(cmsg);
+        if (recvmsg(s, &msg, 0) < 0) {
+		perror("recvmsg");
+		exit(1);
+	}
+	return cmsg.fd;
+}
+
+
+static void child(void)
+{
+	execl(LIBBD_PATH, LIBBD_PATH, NULL);
+	perror(LIBBD_PATH);
+	_exit(1);
+}
+
+
+#if 0
+static int recv_fd(int s)
+{
+	pid_t res;
+
+	res = waitpid(pid, &status, 0);
+	if (res < 0) {
+		perror("waitpid");
+		exit(1);
+	}
+	if (res != pid) {
+		fprintf(stderr, "waitpid returned %d for %d\n",
+		    (int) res, (int) pid);
+		exit(1);
+	}
+}
+#endif
+
+
+static int bbd(void)
+{
+	int s[2];
+	pid_t pid;
+
+	if (socketpair(PF_LOCAL, SOCK_DGRAM, 0, s) < 0) {
+		perror("socketpair");
+		exit(1);
+	}
+	if (dup2(s[1], 1) < 0) {
+		perror("dup2");
+		exit(1);
+	}
+
+	pid = fork();
+	if (pid < 0) {
+		perror("fork");
+		exit(1);
+	}
+	if (pid)
+		return recv_fd(s[0]);
+	else
+		child();
+	return -1; /* can't happen */
+}
+
+
+void libbb_open(void)
+{
+	bbd_fd = bbd();
+	libbb_mem = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED,
+	   bbd_fd, LIBBB_GPIO_BASE);
+	if (libbb_mem == MAP_FAILED) {
+		perror("mmap");
+		exit(1);
+	}
+}
+
+
+
+void libbb_close(void)
+{
+	if (close(bbd_fd) < 0) {
+		perror("close");
+		exit(1);
+	}
+}