Could someone please carefully explain or show a Write Memory Command example (using USART)? (Ref. AN3155, pages 18 - 21) The main confusion is what to send after 'Byte 8' , below I try to show an example of writing 0x42424242 to 0x200001a0 (in RAM).

[SKitt]

Sent: 0x7F // Test Pattern

Received: 0x79 // ACK

Sent byte 1: 0x31    // WRITE command

Sent byte 2: 0xCE // WRITE command complement

Received:   0x79 // ACK   

Sent byte 3: 0x20   // Destination address MSB

Sent byte 4: 0x00

Sent byte 5: 0x01

Sent byte 6: 0xA0    // Destination address LSB

Sent byte 7: 0x24 // Checksum = 0x20 ^ 0x00 ^ 0x01 ^ 0xa0 = 0x81

Received: 0x79 // ACK

Sent byte 8: 0x04 // N = 4 (number of bytes to send)

Sent 0x42 // This is where I start to get confused

Sent 0x42

Sent 0x42

Sent 0x42

Sent 0x04 // Checksum = 0x04 ^ 0x42 ^ 0x42 ^ 0x42 ^ 0x42 = 0x04

Received: 0x1F // NACK

Also tried with N=5 (with Checksum= 0x05), because AN3155 confusingly shows 'N+1' , with same results.

Please, please, please do not oversimplify your answer and thank you for reading my question.

[TDK]

Byte 8 is the number of bytes to send minus one. So sending a 3 means you need to send 4 data bytes. So

(Byte 😎 send 3

send 4 data bytes

send checksum

wait for ack

Yes, the AN is misleading and could be written better on this point.

Note that you must write a multiple of 4 bytes

[SKitt]

Thank you for your reply, TDK.

I have modified the code, but the result is the same:

Sent byte 8: 0x03   // N = 3 (number of bytes to send)

Sent 0x42       // This is where I start to get confused

Sent 0x42

Sent 0x42

Sent 0x42

Sent 0x03       // Checksum = 0x03 ^ 0x42 ^ 0x42 ^ 0x42 ^ 0x42 = 0x03

Received:   0x1F   // NACK

The data 0x42424242 is divided into sending 0x42 four times; so, that complies with the "multiple of 4 bytes" note in AN3155 - right?

Any other thoughts on how to do this?

[TDK]

It looks like you’re writing to RAM, not FLASH. Isnt 0x200001A0 in ram? Doesn't flash start at 0x08000000?

edit: apparently this should work for both flash and ram. Im not sure. I can look at my code in a day and let you know if I see anything off.

[SKitt]

Yes, that is correct. This example is for RAM but the Write Memory Command should work with any memory region with user privileges.

[SKitt]

For verification purposes, I modified the destination address to 0x08001020 (a null spot in Flash) and had the exact same result as with the RAM region. Thank you for your correspondence.

EDIT: Sorry. I failed to note a compilation error before uploading the code. After fixing that and retrying, the writing to this Flash address and region works. =)

In other words, now 0x08001020 = 42424242.

[Tesla DeLorean]

What part?

Write deeper into RAM, the system loader might expect to be using some of it.

[SKitt]

Yes, that is correct. In accordance with the 'Note' on pg 18/38 of AN3155: "When writing to the RAM, user must not overlap the first RAM used by the bootloader

firmware."

I re-modified the destination address for a higher address in RAM and now it works: 0x20001020 = 42424242

Thank you both for helping me through this stone wall.

Points to TDK for helping me modify the 4 to a 3 ( N-1). [Note for ST: please correct this in the AN3155]

Points to Clive Two.Zero for reminding me of the Note on pg 18/35.