I finally got the 'Serial' upload method working on both my blue pill devices with a FTDI USB-Serial adaptor. I found a very good/understandable tutorial
here.
Here's the (non-verbose) output:
Compiling 'BluePill' for 'Generic STM32F103C series(stm32duino_genericSTM32F103C)'
Program size: 11840 bytes (used 18% of a 65536 byte maximum) (0.18 secs)
Minimum Memory Usage: 1432 bytes (7% of a 20480 byte maximum)
Uploading 'BluePill' to 'Generic STM32F103C series(stm32duino_genericSTM32F103C)' using 'COM15'
Resetting to bootloader via Serial
stm32flash 0.4
http://stm32flash.googlecode.com/ Using Parser : Raw BINARY
Interface serial_w32: 115200 8E1
Version : 0x22
Option 1 : 0x00
Option 2 : 0x00
Device ID : 0x0410 (Medium-density)
- RAM : 20KiB (512b reserved by bootloader)
- Flash : 128KiB (sector size: 4x1024)
- Option RAM : 16b
- System RAM : 2KiB
Write to memory
Erasing memory
Wrote address 0x08000100 (2.16%)
Wrote address 0x08000200 (4.32%)
Wrote address 0x08000300 (6.49%)
Wrote address 0x08000400 (8.65%)
Wrote address 0x08000500 (10.81%)
Wrote address 0x08000600 (12.97%)
Wrote address 0x08000700 (15.14%)
Wrote address 0x08000800 (17.30%)
Wrote address 0x08000900 (19.46%)
Wrote address 0x08000a00 (21.62%)
Wrote address 0x08000b00 (23.78%)
Wrote address 0x08000c00 (25.95%)
Wrote address 0x08000d00 (28.11%)
Wrote address 0x08000e00 (30.27%)
Wrote address 0x08000f00 (32.43%)
Wrote address 0x08001000 (34.59%)
Wrote address 0x08001100 (36.76%)
Wrote address 0x08001200 (38.92%)
Wrote address 0x08001300 (41.08%)
Wrote address 0x08001400 (43.24%)
Wrote address 0x08001500 (45.41%)
Wrote address 0x08001600 (47.57%)
Wrote address 0x08001700 (49.73%)
Wrote address 0x08001800 (51.89%)
Wrote address 0x08001900 (54.05%)
Wrote address 0x08001a00 (56.22%)
Wrote address 0x08001b00 (58.38%)
Wrote address 0x08001c00 (60.54%)
Wrote address 0x08001d00 (62.70%)
Wrote address 0x08001e00 (64.86%)
Wrote address 0x08001f00 (67.03%)
Wrote address 0x08002000 (69.19%)
Wrote address 0x08002100 (71.35%)
Wrote address 0x08002200 (73.51%)
Wrote address 0x08002300 (75.68%)
Wrote address 0x08002400 (77.84%)
Wrote address 0x08002500 (80.00%)
Wrote address 0x08002600 (82.16%)
Wrote address 0x08002700 (84.32%)
Wrote address 0x08002800 (86.49%)
Wrote address 0x08002900 (88.65%)
Wrote address 0x08002a00 (90.81%)
Wrote address 0x08002b00 (92.97%)
Wrote address 0x08002c00 (95.14%)
Wrote address 0x08002d00 (97.30%)
Wrote address 0x08002e00 (99.46%)
Wrote address 0x08002e40 (100.00%) Done.
Starting execution at address 0x08000000... done.
The upload process has finished.