board: add configuration for stm32f103c8 "Blue Pill"

The "Blue Pill" is a popular development board with an STM32F103C8
micro controller. According to sources, it has a 128kB Flash on board
even though the option bytes only report 64kB. This patch therefore also
modifies target/stm32f1x.cfg to take an optional FLASH_SIZE variable into
account which the board file sets to 0x20000.

Change-Id: I8a78ccd2b5faf637c539ee3cf8136789ee15c95d
Signed-off-by: Matthias Welwarsky <matthias.welwarsky@sysgo.com>
Reviewed-on: http://openocd.zylin.com/4495
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

tcl/board/stm32f103c8_blue_pill.cfg

@@ -0,0 +1,14 @@
+# STM32F103C8 "Blue Pill"
+
+# NOTE:
+# There is a fair bit of confusion about whether the "Blue Pill" has 128kB or 64kB flash size.
+# The most likely cause is that there exist a -C8 and a -CB variant of the STM32F103, where
+# the C8 has 64kB, the CB has 128kB as per specification. "Blue Pill" boards are manufactured
+# by a lot of different vendors, some may actually use the CB variant but from a cursory look
+# it very hard to tell them apart ("C8" and "CB" look very similar). Nevertheless, people have
+# tried using the full 128kB of flash on the C8 and found it to be working. Hence this board file
+# overrides the internal size detection. Be aware though that you may be using you particular
+# board outside of its specification. If in doubt, comment the following line.
+set FLASH_SIZE 0x20000
+
+source [find target/stm32f1x.cfg]

tcl/target/stm32f1x.cfg

@@ -22,6 +22,14 @@ if { [info exists WORKAREASIZE] } {
    set _WORKAREASIZE 0x1000
 }
 
+# Allow overriding the Flash bank size
+if { [info exists FLASH_SIZE] } {
+    set _FLASH_SIZE $FLASH_SIZE
+} else {
+    # autodetect size
+    set _FLASH_SIZE 0
+}
+
 #jtag scan chain
 if { [info exists CPUTAPID] } {
    set _CPUTAPID $CPUTAPID
@@ -49,7 +57,7 @@ $_TARGETNAME configure -work-area-phys 0x20000000 -work-area-size $_WORKAREASIZE
 
 # flash size will be probed
 set _FLASHNAME $_CHIPNAME.flash
-flash bank $_FLASHNAME stm32f1x 0x08000000 0 0 0 $_TARGETNAME
+flash bank $_FLASHNAME stm32f1x 0x08000000 $_FLASH_SIZE 0 0 $_TARGETNAME
 
 # JTAG speed should be <= F_CPU/6. F_CPU after reset is 8MHz, so use F_JTAG = 1MHz
 adapter_khz 1000