devmem: new applet

3 files changed, 131 insertions, 0 deletions

diff --git a/miscutils/Config.in b/miscutils/Config.in
index 074e6c41f..f8b4575e0 100644
--- a/miscutils/Config.in
+++ b/miscutils/Config.in
@@ -196,6 +196,13 @@ config FEATURE_DEVFS
 	  /dev/loop0. If your /dev directory has normal names instead of
 	  devfs names, you don't want this.
 
+config DEVMEM
+	bool "devmem"
+	default n
+	help
+	  devmem is a small program that reads and writes from physical
+	  memory using /dev/mem.
+
 config EJECT
 	bool "eject"
 	default n
diff --git a/miscutils/Kbuild b/miscutils/Kbuild
index c12b12d42..13791ef18 100644
--- a/miscutils/Kbuild
+++ b/miscutils/Kbuild
@@ -13,6 +13,7 @@ lib-$(CONFIG_CROND)       += crond.o
 lib-$(CONFIG_CRONTAB)     += crontab.o
 lib-$(CONFIG_DC)          += dc.o
 lib-$(CONFIG_DEVFSD)      += devfsd.o
+lib-$(CONFIG_DEVMEM)      += devmem.o
 lib-$(CONFIG_EJECT)       += eject.o
 lib-$(CONFIG_FBSPLASH)    += fbsplash.o
 lib-$(CONFIG_HDPARM)      += hdparm.o
diff --git a/miscutils/devmem.c b/miscutils/devmem.c
new file mode 100644
index 000000000..8b8edbe7c
--- /dev/null
+++ b/miscutils/devmem.c
@@ -0,0 +1,123 @@
+/*
+ * Licensed under the GPL v2 or later, see the file LICENSE in this tarball.
+ *  Copyright (C) 2000, Jan-Derk Bakker (J.D.Bakker@its.tudelft.nl)
+ *  Copyright (C) 2008, BusyBox Team. -solar 4/26/08
+ */
+
+#include "libbb.h"
+
+#define DEVMEM_MAP_SIZE 4096
+#define DEVMEM_MAP_MASK (off_t)(DEVMEM_MAP_SIZE - 1)
+
+int devmem_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int devmem_main(int argc UNUSED_PARAM, char **argv)
+{
+	void *map_base, *virt_addr;
+	uint64_t read_result;
+	uint64_t writeval = writeval; /* for compiler */
+	off_t target;
+	int fd;
+	int width = 8 * sizeof(int);
+
+	/* devmem ADDRESS [WIDTH [VALUE]] */
+
+	/* ADDRESS */
+	if (!argv[1])
+		bb_show_usage();
+	errno = 0;
+	target = bb_strtoull(argv[1], NULL, 0); /* allows hex, oct etc */
+
+	/* WIDTH */
+	if (argv[2]) {
+		if (isdigit(argv[2][0]) || argv[2][1])
+			width = xatou(argv[2]);
+		else {
+			static const char bhwl[] ALIGN1 = "bhwl";
+			static const uint8_t sizes[] ALIGN1 = {
+				8 * sizeof(char),
+				8 * sizeof(short),
+				8 * sizeof(int),
+				8 * sizeof(long),
+				0 /* bad */
+			};
+			width = strchrnul(bhwl, (argv[2][0] | 0x20)) - bhwl;
+			width = sizes[width];
+		}
+		/* VALUE */
+		if (argv[3])
+			writeval = bb_strtoull(argv[3], NULL, 0);
+	} else { /* argv[2] == NULL */
+		/* make argv[3] to be a valid thing to use */
+		argv--;
+	}
+	if (errno)
+		bb_show_usage(); /* bb_strtouXX failed */
+
+	fd = xopen("/dev/mem", argv[3] ? (O_RDWR | O_SYNC) : (O_RDONLY | O_SYNC));
+
+	map_base = mmap(NULL,
+			DEVMEM_MAP_SIZE * 2 /* in case value spans page */,
+			argv[3] ? (PROT_READ | PROT_WRITE) : PROT_READ,
+			MAP_SHARED,
+			fd,
+			target & ~DEVMEM_MAP_MASK);
+	if (map_base == MAP_FAILED)
+		bb_perror_msg_and_die("mmap");
+
+//	printf("Memory mapped at address %p.\n", map_base);
+
+	virt_addr = (char*)map_base + (target & DEVMEM_MAP_MASK);
+
+	switch (width) {
+	case 8:
+		read_result = *(volatile uint8_t*)virt_addr;
+		break;
+	case 16:
+		read_result = *(volatile uint16_t*)virt_addr;
+		break;
+	case 32:
+		read_result = *(volatile uint32_t*)virt_addr;
+		break;
+	case 64:
+		read_result = *(volatile uint64_t*)virt_addr;
+		break;
+	default:
+		bb_error_msg_and_die("bad width");
+	}
+
+	printf("Value at address 0x%"OFF_FMT"X (%p): 0x%llX\n",
+			target, virt_addr,
+			(unsigned long long)read_result);
+
+	if (argv[3]) {
+		switch (width) {
+		case 8:
+			*(volatile uint8_t*)virt_addr = writeval;
+			read_result = *(volatile uint8_t*)virt_addr;
+			break;
+		case 16:
+			*(volatile uint16_t*)virt_addr = writeval;
+			read_result = *(volatile uint16_t*)virt_addr;
+			break;
+		case 32:
+			*(volatile uint32_t*)virt_addr = writeval;
+			read_result = *(volatile uint32_t*)virt_addr;
+			break;
+		case 64:
+			*(volatile uint64_t*)virt_addr = writeval;
+			read_result = *(volatile uint64_t*)virt_addr;
+			break;
+		}
+		printf("Written 0x%llX; readback 0x%llX\n",
+				(unsigned long long)writeval,
+				(unsigned long long)read_result);
+	}
+
+	if (ENABLE_FEATURE_CLEAN_UP) {
+		if (munmap(map_base, DEVMEM_MAP_SIZE) == -1)
+			bb_perror_msg_and_die("munmap");
+		close(fd);
+	}
+
+	return EXIT_SUCCESS;
+}