Bootloader read memory command fails

[Clament John]

Posted on June 13, 2017 at 09:14

I'm using an STM32F103 and flashing a code into it using the bootloader. I'm successful in writing the code into the MCU, but when I try reading it using the Read Memory command (pg13) [

http://www.st.com/content/ccc/resource/technical/document/application_note/51/5f/03/1e/bd/9b/45/be/CD00264342.pdf/files/CD00264342.pdf/jcr:content/translations/en.CD00264342.pdf

] it fails at step 6 (Send the number of bytes to be read (1 byte) & a checksum (1 byte).)  I receive a NACK. It's confusing here, so I tried sending both XOR of 8th byte with 0 and in the next try tried sending complement of 8th byte, both failed.

Here's what I'm doing:

1. Read 128 byte of the file to be written from SD card 

2. Write this 128 bytes into the STM32 flash (code space) through the boot loader //works perfectly fine

3. Read back the recently written 128 bytes to verify if the write was successful.

4. If data written == read, move on. Write the next set of data. 

5. Loop till the whole file has been written.

6. Send GO command and reset the STM.

P.S. I know the write command is working because previously I only had the write command, and it was working in the field. But some devices were flashed with the wrong/ corrupted code. So I'm reading back and checking if the data were written is the right one.

#stm32 #boot-loader

[noobsen]

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@Clament John wrote:
Posted on June 13, 2017 at 09:14

... but when I try reading it using the Read Memory command it fails at step 6 (Send the number of bytes to be read (1 byte) & a checksum (1 byte).)  I receive a NACK. It's confusing here, so I tried sending both XOR of 8th byte with 0 and in the next try tried sending complement of 8th byte, both failed ...

#stm32 #boot-loader

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Hi, 

it is an old issue but I had the same problem. I think there is specification failure. Try to add +1 to calculate the check sum for the amount of data you want to receive. This solves the problem for me.

example you want to get 128 bytes:  0x7F (data), 0x7F (checksum) => NACK 
correct: 0x7F (data), 0x80 (checksum) => OK 

[Tesla DeLorean]

I'm not convinced.

Show an actual transactional example. I don't recall having issues with the AN3155 protocol docs and F1 parts, but the docs have likely been reworked a few times in the last 15+ years 

[noobsen]

What should I say. The current specification AN3155 doesn't work with a STMF103C8 for the Read Memory Command. It takes me one day to find a solution for this error.

AN3155

If you take Byte 8 (127) and make a XOR of Byte 8 (127) for Byte 9, you will get a NACK.
If you take Byte 8 (127) and make a XOR of Byte 8 +1 (128) for Byte 9, you will get an OK.

I found this solution by sniffing the communication of the old program "Flash Loader Demo".
But this is only for the Read Memory Command and there only for Byte 9!

[brymat]

I think I have figured this out as I was having the same issue.  The key is the wording in AN3155:

"Checksum: XOR byte 8 (complement of byte 8)"

It actually means that the second byte is the complement of the first byte.  In C, this would be the ~ operator.  This is the same as the command byte.

Example 1:

Byte 0 = 0x01 (Read 2 bytes)

Byte 1 = 0xFE

Example 2:

Byte 0 = 0x7F (Read 128 byte)

Byte 1 = 0x80