$ st-flash erase
st-flash 1.5.1-22-g4ff515e-dirty
2019-04-05T10:11:45 INFO usb.c: -- exit_dfu_mode
2019-04-05T10:11:45 INFO common.c: Loading device parameters....
2019-04-05T10:11:45 INFO common.c: Device connected is: F1 Medium-density device, id 0x20036410
2019-04-05T10:11:45 INFO common.c: SRAM size: 0x5000 bytes (20 KiB), Flash: 0x10000 bytes (64 KiB) in pages of 1024 bytes
Mass erasing

$ st-flash write blackmagic_dfu.bin 0x8000000
st-flash 1.5.1-22-g4ff515e-dirty
2019-04-05T10:16:09 INFO common.c: Loading device parameters....
2019-04-05T10:16:09 INFO common.c: Device connected is: F1 Medium-density device, id 0x20036410
2019-04-05T10:16:09 INFO common.c: SRAM size: 0x5000 bytes (20 KiB), Flash: 0x10000 bytes (64 KiB) in pages of 1024 bytes
2019-04-05T10:16:09 INFO common.c: Attempting to write 7348 (0x1cb4) bytes to stm32 address: 134217728 (0x8000000)
Flash page at addr: 0x08001c00 erased
2019-04-05T10:16:10 INFO common.c: Finished erasing 8 pages of 1024 (0x400) bytes
2019-04-05T10:16:10 INFO common.c: Starting Flash write for VL/F0/F3/F1_XL core id
2019-04-05T10:16:10 INFO flash_loader.c: Successfully loaded flash loader in sram
  8/8 pages written
2019-04-05T10:16:10 INFO common.c: Starting verification of write complete
2019-04-05T10:16:10 INFO common.c: Flash written and verified! jolly good!

$ st-flash --flash=0x20000 write blackmagic.bin 0x8002000
st-flash 1.5.1-22-g4ff515e-dirty
2019-04-05T10:33:21 INFO common.c: Loading device parameters....
2019-04-05T10:33:21 INFO common.c: Device connected is: F1 Medium-density device, id 0x20036410
2019-04-05T10:33:21 INFO common.c: SRAM size: 0x5000 bytes (20 KiB), Flash: 0x10000 bytes (64 KiB) in pages of 1024 bytes
Forcing flash size: --flash=0x00020000
2019-04-05T10:33:21 INFO common.c: Attempting to write 73244 (0x11e1c) bytes to stm32 address: 134225920 (0x8002000)
Flash page at addr: 0x08013c00 erased
2019-04-05T10:33:23 INFO common.c: Finished erasing 72 pages of 1024 (0x400) bytes
2019-04-05T10:33:23 INFO common.c: Starting Flash write for VL/F0/F3/F1_XL core id
2019-04-05T10:33:23 INFO flash_loader.c: Successfully loaded flash loader in sram
 72/72 pages written
2019-04-05T10:33:27 INFO common.c: Starting verification of write complete
2019-04-05T10:33:29 INFO common.c: Flash written and verified! jolly good!