diff --git a/embed/extmod/modtrezorio/modtrezorio-sdcard.h b/embed/extmod/modtrezorio/modtrezorio-sdcard.h
index 3298615f9..f8006bd36 100644
--- a/embed/extmod/modtrezorio/modtrezorio-sdcard.h
+++ b/embed/extmod/modtrezorio/modtrezorio-sdcard.h
@@ -21,6 +21,9 @@ STATIC mp_obj_t mod_trezorio_SDCard_make_new(const mp_obj_type_t *type, size_t n
     mp_arg_check_num(n_args, n_kw, 0, 0, false);
     mp_obj_SDCard_t *o = m_new_obj(mp_obj_SDCard_t);
     o->base.type = type;
+#if defined TREZOR_UNIX
+    sdcard_init();
+#endif
     return MP_OBJ_FROM_PTR(o);
 }
 
diff --git a/embed/unix/sdcard.c b/embed/unix/sdcard.c
index b3fcc0378..1f48a861f 100644
--- a/embed/unix/sdcard.c
+++ b/embed/unix/sdcard.c
@@ -5,31 +5,95 @@
  * see LICENSE file for details
  */
 
+#include <string.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#include "common.h"
 #include "sdcard.h"
 
+#ifndef SDCARD_FILE
+#define SDCARD_FILE "/var/tmp/trezor.sdcard"
+#endif
+
+#define SDCARD_SIZE (32 * 1024 * 1024)
+
+static uint8_t *sdcard_buffer;
+static secbool sdcard_powered;
+
+static void sdcard_exit(void)
+{
+    int r = munmap(sdcard_buffer, SDCARD_SIZE);
+    ensure(sectrue * (r == 0), "munmap failed");
+}
+
 void sdcard_init(void) {
+    int r;
+
+    // check whether the file exists and it has the correct size
+    struct stat sb;
+    r = stat(SDCARD_FILE, &sb);
+
+    // (re)create if non existant or wrong size
+    if (r != 0 || sb.st_size != SDCARD_SIZE) {
+        int fd = open(SDCARD_FILE, O_RDWR | O_CREAT | O_TRUNC, (mode_t)0600);
+        ensure(sectrue * (fd >= 0), "open failed");
+        for (int i = 0; i < SDCARD_SIZE / 16; i++) {
+            ssize_t s = write(fd, "\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF\xFF", 16);
+            ensure(sectrue * (s >= 0), "write failed");
+        }
+        r = close(fd);
+        ensure(sectrue * (r == 0), "close failed");
+    }
+
+    // mmap file
+    int fd = open(SDCARD_FILE, O_RDWR);
+    ensure(sectrue * (fd >= 0), "open failed");
+
+    void *map = mmap(0, SDCARD_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+    ensure(sectrue * (map != MAP_FAILED), "mmap failed");
+
+    sdcard_buffer = (uint8_t *)map;
+
+    sdcard_powered = secfalse;
+
+    atexit(sdcard_exit);
 }
 
 secbool sdcard_is_present(void) {
-    return secfalse;
+    return sectrue;
 }
 
 secbool sdcard_power_on(void) {
-    return secfalse;
+    sdcard_powered = sectrue;
+    return sectrue;
 }
 
 secbool sdcard_power_off(void) {
+    sdcard_powered = secfalse;
     return sectrue;
 }
 
 uint64_t sdcard_get_capacity_in_bytes(void) {
-    return 0;
+    return sdcard_powered == sectrue ? SDCARD_SIZE : 0;
 }
 
 secbool sdcard_read_blocks(uint32_t *dest, uint32_t block_num, uint32_t num_blocks) {
-   return secfalse;
+    if (sectrue != sdcard_powered) {
+        return secfalse;
+    }
+    memcpy(dest, sdcard_buffer + block_num * SDCARD_BLOCK_SIZE, num_blocks * SDCARD_BLOCK_SIZE);
+    return sectrue;
 }
 
 secbool sdcard_write_blocks(const uint32_t *src, uint32_t block_num, uint32_t num_blocks) {
-   return secfalse;
+    if (sectrue != sdcard_powered) {
+        return secfalse;
+    }
+    memcpy(sdcard_buffer + block_num * SDCARD_BLOCK_SIZE, src, num_blocks * SDCARD_BLOCK_SIZE);
+    return sectrue;
 }
diff --git a/tests/test_trezor.io.py b/tests/test_trezor.io.py
index bd0f499ee..c960726f8 100644
--- a/tests/test_trezor.io.py
+++ b/tests/test_trezor.io.py
@@ -2,11 +2,47 @@ from common import *
 
 from trezor import io
 
+
 class TestIo(unittest.TestCase):
 
-    def test_sdcard(self):
+    def test_sdcard_start(self):
         sd = io.SDCard()
-        sd.present()
+        assert sd.present() == True
+
+    def test_sdcard_power(self):
+        sd = io.SDCard()
+        x = bytearray(8 * 512)
+        assert sd.capacity() == 0
+        assert sd.read(0, x) == False
+        sd.power(True)
+        assert sd.capacity() > 0
+        assert sd.read(0, x) == True
+        sd.power(False)
+        assert sd.capacity() == 0
+        assert sd.read(0, x) == False
+
+    def test_sdcard_read(self):
+        sd = io.SDCard()
+        x = bytearray(8 * 512)
+        sd.power(True)
+        assert sd.read(0, x) == True
+        sd.power(False)
+        assert sd.read(0, x) == False
+
+    def test_sdcard_read_write(self):
+        sd = io.SDCard()
+        r = bytearray(8 * 512)
+        w0 = bytearray(b'0' * (8 * 512))
+        w1 = bytearray(b'1' * (8 * 512))
+        sd.power(True)
+        assert sd.write(0, w0) == True
+        assert sd.read(0, r) == True
+        assert r == w0
+        assert sd.write(0, w1) == True
+        assert sd.read(0, r) == True
+        assert r == w1
+        sd.power(False)
+
 
 if __name__ == '__main__':
     unittest.main()