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Decoding STM32F042 Unique ID

Question asked by Valentin on Nov 14, 2016
Hello everyone,

as I (too) am looking for a way to give my controller a unqie ID, I'm currently trying to decode and understand the built in unique_id register.

So according to the refmanual, the Data sits at address 0x1FFFF7AC with offsets 0x00, 0x04 and 0x08.

0x00 gives: UID[31:0]: X and Y coordinates on the wafer expressed in BCD format
0x04 gives: Bits 31:8 UID[63:40]: LOT_NUM[23:0] - Lot number (ASCII encoded)
Bits 7:0 UID[39:32]: WAF_NUM[7:0] - Wafer number (8-bit unsigned number)
and 0x08 gives: Bits 31:0 UID[95:64]: LOT_NUM[55:24] Lot number (ASCII encoded)

The following code is what I made of that information:

#define ADDR_UID 0x1FFFF7AC
 
typedef union longlong_ascii{
    long long in_long;
    char ascii[7];
}longlong_ascii;
 
typedef struct stm32_uid {
    uint16_t x, y;
    uint8_t WAF_NUM;
    longlong_ascii LOT_NUM;
}stm32_uid;
 
volatile stm32_uid device_id = {
        .x = (*(uint32_t *) ADDR_UID) & 0xFFFF, //not sure whether this is x or y
        .y = ((*(uint32_t *) ADDR_UID) & 0xFFFF0000) >> 16, // again x? or y?
        .WAF_NUM = (*(uint32_t *) (ADDR_UID + 0x04)) & 0xFF,
        .LOT_NUM = {((*(long long *) (ADDR_UID + 0x04)) & 0xFFFFFFFFFFFFFF00)},
};


The results are for my specific chip:
x = 32
y = 12
WAF_NUM = 5
LOT_NUM.ascii = "042ACC\0"

raw data:
*(uint32_t *) 0x1FFFF7AC = 0xc0020
*(uint32_t *) (0x1FFFF7AC + 0x04) = 0x41434305
*(uint32_t *) (0x1FFFF7AC + 0x08) = 0x20303432

I think this sounds reasonable and I wanted to share this with you guys, also I'd like to know which way round the x and y coordinates are stored? x in lower bytes? or in higher?
Interesting, that the LOT_NUM actually says "042AAC". I wonder how the counting is done here. Is 042 constant and refers to the F042 series? Is AAC hex counting? The chip marking is:
7846S
32F042F6T6
PHL 511

Thanks!

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