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;
+}