python mmap skipping every second byte when writing -

i have strange problem using mmap in python when writing memory (/dev/mem). clear, reading done in same manner , works ok. when comes writing, seems every second byte unwritable.

ex.

 when read   addr 0x200 val 0x1234  when try write  addr 0x200 val 0x4321  written  addr 0x200 val 0x0021 

when try write byte byte, same happens. ex.

write: addr 0x200 0x43 addr 0x201 0x21 addr 0x200 0x00 addr 0x201 0x21 

code:

class pydump:     def __init__(self, addr, length = 1, word_size = 4, filename = '/dev/mem'):         if addr < 0 or length < 0: raise valueerror('address or length invalid')         self._verbose = verbose          self.word_size = word_size         self.mask = ~(self.word_size - 1)         self.base_addr = addr & ~(mmap.pagesize - 1)         self.addr_offset = addr - self.base_addr         self.word_length = length         self.no_of_bytes = self.word_length * self.word_size          # align length full words         end_addr = addr + self.no_of_bytes         if end_addr % self.mask:             end_addr = (end_addr + self.word_size) & self.mask          self.map_length = end_addr - self.base_addr         self.fname = filename          self.fd = os.open(self.fname, os.o_rdwr | os.o_sync)         self.mem = mmap.mmap(self.fd, self.map_length, mmap.map_shared,                              mmap.prot_read | mmap.prot_write,                              offset=self.base_addr)      def read(self):         mem = self.mem         virt_base_addr = self.addr_offset & self.mask         mem.seek(virt_base_addr)          data = []         in range(self.no_of_bytes):             data.append(struct.unpack('b', mem.read_byte())[0])          abs_addr = self.base_addr + virt_base_addr         return pydumpbuffer(abs_addr, data, self.word_size)      def write(self, data):         mem = self.mem         virt_base_addr = self.addr_offset & self.mask         mem.seek(virt_base_addr)          if self.word_size == 1:             mem.write(struct.pack('b', data))         elif self.word_size == 2:             mem.write(struct.pack('h', data))         elif self.word_size == 4:             mem.write(struct.pack('i', data))         else:             raise valueerror('invalid word size')      def write_bytes(self, bytes):         if len(bytes) != self.no_of_bytes: raise valueerror('wrong number of bytes given')         mem = self.mem         virt_base_addr = self.addr_offset & self.mask         mem.seek(virt_base_addr)          byte in bytes:             mem.write_byte(byte) 

example run (i prepared memory other memdump tool [bin] 0xeeeeeeee):

>>> pydump import pydump memdump >>> memdump(0x18007c20, 1, 4).read() 0xeeeeeeee >>> memdump(0x18007c20, 1, 4).write(0x12345678) >>> memdump(0x18007c20, 1, 4).read() 0x00340078 >>> memdump(0x18007c20, 1, 4).write(0x87654321) >>> memdump(0x18007c20, 1, 4).read() 0x00650021 

example no 2 (i not write 2 bytes @ 'first' byte place):

>>> memdump(0x18007c20, 1, 2).write(0xabcd) >>> memdump(0x18007c20, 1, 4).read() 0x00650021 >>> memdump(0x18007c21, 1, 1).write(0xcd) >>> memdump(0x18007c20, 1, 4).read() 0x00650021 >>> memdump(0x18007c22, 1, 1).write(0xcd) >>> memdump(0x18007c20, 1, 4).read() 0x00cdcd00 

any thoughts on problem ?

i know wrong now. answer it's fault of python specific hardware/driver.

i looked through implementation of mmap , uses memcpy, know copies byte byte. in c implemention did not happen, when needed write 4 bytes, 4 bytes written. here comes limitation of hardware/driver every register must written in full (i did not know @ time of stating question), when writing byte byte weird behaviour.

some registers 16bit , 32bit. when writing 0xffff 16bit register ended having 0x00ff. memcpy copying 0xff twice. driver got write(0xff) write(0xff), doing (because of python) 2 writes register of byte 0xff :) same happened 32bit registers, although looked different (but driver may behave different).

for work have change implementation of python mmap :(