STM32L432Kx Flash Size
The STM32L432Kx is available with two different flash sizes. The STM32L432KB has got 128 kB while the STM32L432KC has got 256 kB. I recently created a USB "key" using the STM32L432. The reason for using this specific STM32 MCU was twofold:
- It is small
- It's got a built-in 48 MHz oscillator precise enough to use USB without an external crystal
Unfortunately, while I wanted the 256 kB version, only the 128 kB version was available.
The STM32 Blue Pill boards mostly use Chinese clone MCUs but there has been a lot of writing about the original ones having 128 kB of flash rather than the 64 kB specified by the datasheet. There is even a test tool available which can test for the hidden flash.
Inspired by this, I decided to test the STM32L432KB on my own board. As per the datasheet this processor is supposed to have 128 kB of flash ranging from 0x8000000 to 0x801FFFF.
Testing
Checking device
lth@ncpws04:~/tmp$ st-info --probe Found 1 stlink programmers version: V2J45S31 serial: 066CFF3933584B3043184346 flash: 131072 (pagesize: 2048) sram: 49152 chipid: 0x435 dev-type: STM32L41x_L42x
Notice that the device reports 128 kB of flash - as is expected.
Generating Test Data
First step is to create a 256 kB file with random data.
lth@ncpws04:~/tmp$ dd if=/dev/urandom of=random.bin bs=1k count=256 256+0 records in 256+0 records out 262144 bytes (262 kB, 256 KiB) copied, 0.0012241 s, 214 MB/s
Writing data to MCU
The random.bin file is of a size which should only be possible to flash on STM32L432KC.
First step is to flash normal:
lth@ncpws04:~/tmp$ st-flash write random.bin 0x8000000 st-flash 1.8.0 2024-09-02T10:30:01 INFO common.c: STM32L41x_L42x: 48 KiB SRAM, 128 KiB flash in at least 2 KiB pages. file random.bin md5 checksum: 5f7ebd5c822e7408e6279445eb1444a, stlink checksum: 0x01fe53dd 2024-09-02T10:30:01 INFO common_flash.c: Attempting to write 262144 (0x40000) bytes to stm32 address: 134217728 (0x8000000) 2024-09-02T10:30:01 ERROR common_flash.c: The size exceeds the size of the flash (0x00020000 bytes available) stlink_fwrite_flash() == -1
As expected this failed. The MCU reports 128 kB of flash and we attempt to write 256 kB. We can however instruct st-flash to ignore that and attempt to write the entire file:
lth@ncpws04:~/tmp$ st-flash --flash=256k write random.bin 0x8000000 st-flash 1.8.0 2024-09-02T10:30:26 INFO common.c: STM32L41x_L42x: 48 KiB SRAM, 128 KiB flash in at least 2 KiB pages. Forcing flash size: --flash=0x00040000 file random.bin md5 checksum: 5f7ebd5c822e7408e6279445eb1444a, stlink checksum: 0x01fe53dd 2024-09-02T10:30:26 INFO common_flash.c: Attempting to write 262144 (0x40000) bytes to stm32 address: 134217728 (0x8000000) EraseFlash - Page:0x10 Size:0x800 -> Flash page at 0x8008000 erased (size: 0x800EraseFlash - Page:0x11 Size:0x800 -> Flash page at 0x8008800 erased (size: 0x800EraseFlash - Page:0x12 Size:0x800 -> Flash page at 0x8009000 erased (size: 0x800EraseFlash - Page:0x13 Size:0x800 -> Flash page at 0x8009800 erased (size: 0x800EraseFlash - Page:0x14 Size:0x800 -> Flash page at 0x800a000 erased (size: 0x800EraseFlash - Page:0x15 Size:0x800 -> Flash page at 0x800a800 erased (size: 0x800EraseFlash - Page:0x16 Size:0x800 -> Flash page at 0x800b000 erased (size: 0x800EraseFlash - Page:0x17 Size:0x800 -> Flash page at 0x800b800 erased (size: 0x800EraseFlash - Page:0x18 Size:0x800 -> Flash page at 0x800c000 erased (size: 0x800EraseFlash - Page:0x19 Size:0x800 -> Flash page at 0x800c800 erased (size: 0x800EraseFlash - Page:0x1a Size:0x800 -> Flash page at 0x800d000 erased (size: 0x800EraseFlash - Page:0x1b Size:0x800 -> Flash page at 0x800d800 erased (size: 0x800EraseFlash - Page:0x1c Size:0x800 -> Flash page at 0x800e000 erased (size: 0x800EraseFlash - Page:0x1d Size:0x800 -> Flash page at 0x800e800 erased (size: 0x800EraseFlash - Page:0x1e Size:0x800 -> Flash page at 0x800f000 erased (size: 0x800EraseFlash - Page:0x1f Size:0x800 -> Flash page at 0x800f800 erased (size: 0x800EraseFlash - Page:0x20 Size:0x800 -> Flash page at 0x8010000 erased (size: 0x800EraseFlash - Page:0x21 Size:0x800 -> Flash page at 0x8010800 erased (size: 0x800EraseFlash - Page:0x22 Size:0x800 -> Flash page at 0x8011000 erased (size: 0x800EraseFlash - Page:0x23 Size:0x800 -> Flash page at 0x8011800 erased (size: 0x800EraseFlash - Page:0x24 Size:0x800 -> Flash page at 0x8012000 erased (size: 0x800EraseFlash - Page:0x25 Size:0x800 -> Flash page at 0x8012800 erased (size: 0x800EraseFlash - Page:0x26 Size:0x800 -> Flash page at 0x8013000 erased (size: 0x800EraseFlash - 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Page:0x68 Size:0x800 -> Flash page at 0x8034000 erased (size: 0x800EraseFlash - Page:0x69 Size:0x800 -> Flash page at 0x8034800 erased (size: 0x800EraseFlash - Page:0x6a Size:0x800 -> Flash page at 0x8035000 erased (size: 0x800EraseFlash - Page:0x6b Size:0x800 -> Flash page at 0x8035800 erased (size: 0x800EraseFlash - Page:0x6c Size:0x800 -> Flash page at 0x8036000 erased (size: 0x800EraseFlash - Page:0x6d Size:0x800 -> Flash page at 0x8036800 erased (size: 0x800EraseFlash - Page:0x6e Size:0x800 -> Flash page at 0x8037000 erased (size: 0x800EraseFlash - Page:0x6f Size:0x800 -> Flash page at 0x8037800 erased (size: 0x800EraseFlash - Page:0x70 Size:0x800 -> Flash page at 0x8038000 erased (size: 0x800EraseFlash - Page:0x71 Size:0x800 -> Flash page at 0x8038800 erased (size: 0x800EraseFlash - Page:0x72 Size:0x800 -> Flash page at 0x8039000 erased (size: 0x800EraseFlash - Page:0x73 Size:0x800 -> Flash page at 0x8039800 erased (size: 0x800EraseFlash - Page:0x74 Size:0x800 -> Flash page at 0x803a000 erased (size: 0x800EraseFlash - Page:0x75 Size:0x800 -> Flash page at 0x803a800 erased (size: 0x800EraseFlash - Page:0x76 Size:0x800 -> Flash page at 0x803b000 erased (size: 0x800EraseFlash - Page:0x77 Size:0x800 -> Flash page at 0x803b800 erased (size: 0x800EraseFlash - Page:0x78 Size:0x800 -> Flash page at 0x803c000 erased (size: 0x800EraseFlash - Page:0x79 Size:0x800 -> Flash page at 0x803c800 erased (size: 0x800EraseFlash - Page:0x7a Size:0x800 -> Flash page at 0x803d000 erased (size: 0x800EraseFlash - Page:0x7b Size:0x800 -> Flash page at 0x803d800 erased (size: 0x800EraseFlash - Page:0x7c Size:0x800 -> Flash page at 0x803e000 erased (size: 0x800EraseFlash - Page:0x7d Size:0x800 -> Flash page at 0x803e800 erased (size: 0x800EraseFlash - Page:0x7e Size:0x800 -> Flash page at 0x803f000 erased (size: 0x800EraseFlash - Page:0x7f Size:0x800 -> Flash page at 0x803f800 erased (size: 0x800) 2024-09-02T10:30:29 INFO flash_loader.c: Starting Flash write for F2/F4/F7/L4 2024-09-02T10:30:29 INFO flash_loader.c: Successfully loaded flash loader in sram 2024-09-02T10:30:29 INFO flash_loader.c: Clear DFSR 2024-09-02T10:30:35 INFO common_flash.c: Starting verification of write complete 2024-09-02T10:30:37 INFO common_flash.c: Flash written and verified! jolly good!
That went well - no errors reported. Now let's try to read that flash into a file:
Reading data from the MCU
To be absolutely certain, read the data back into a new file:
lth@ncpws04:~/tmp$ st-flash --flash=256k read random2.bin 0x8000000 0x40000 st-flash 1.8.0 2024-09-02T10:31:51 INFO common.c: STM32L41x_L42x: 48 KiB SRAM, 128 KiB flash in at least 2 KiB pages. Forcing flash size: --flash=0x00040000 2024-09-02T10:31:51 INFO common.c: read from address 0x08000000 size 262144
No complaints!
Compare data
Finally we can verify that the data read from the MCU matches the data we wrote to the MCU:
lth@ncpws04:~/tmp$ md5sum random* 5f7ebd5c822e07408e6279445eb1444a random2.bin 5f7ebd5c822e07408e6279445eb1444a random.bin
They are identical, so it is absolutely confirmed that this particular STM32L432KB is in fact a STM32L432KC which identifies as a STM32L432KB.