shell.nix: add teensy loader

[qmk_firmware.git] / docs / faq_debug.md

diff --git a/docs/faq_debug.md b/docs/faq_debug.md
index 9e76ac409407db81b1a85c336a136e55f2858ea8..df35fbb986766988bcd8dad1efecdd7590e54ef8 100644 (file)
--- a/docs/faq_debug.md
+++ b/docs/faq_debug.md
@@ -48,12 +48,51 @@ SUBSYSTEMS=="usb", ATTRS{idVendor}=="feed", MODE:="0666"
 ***
 
 # Miscellaneous
+## Safety Considerations
+
+You probably don't want to "brick" your keyboard, making it impossible
+to rewrite firmware onto it.  Here are some of the parameters to show
+what things are (and likely aren't) too risky.
+
+- If your keyboard map does not include RESET, then, to get into DFU
+  mode, you will need to press the reset button on the PCB, which
+  requires unscrewing the bottom.
+- Messing with tmk_core / common files might make the keyboard
+  inoperable
+- Too large a .hex file is trouble; `make dfu` will erase the block,
+  test the size (oops, wrong order!), which errors out, failing to
+  flash the keyboard, leaving it in DFU mode.
+  - To this end, note that the maximum .hex file size on Planck is
+    7000h (28672 decimal)
+
+```
+Linking: .build/planck_rev4_cbbrowne.elf                                                            [OK]
+Creating load file for Flash: .build/planck_rev4_cbbrowne.hex                                       [OK]
+
+Size after:
+   text    data     bss     dec     hex filename
+      0   22396       0   22396    577c planck_rev4_cbbrowne.hex
+```
+
+  - The above file is of size 22396/577ch, which is less than
+    28672/7000h
+  - As long as you have a suitable alternative .hex file around, you
+    can retry, loading that one
+  - Some of the options you might specify in your keyboard's Makefile
+    consume extra memory; watch out for BOOTMAGIC_ENABLE,
+    MOUSEKEY_ENABLE, EXTRAKEY_ENABLE, CONSOLE_ENABLE, API_SYSEX_ENABLE
+- DFU tools do /not/ allow you to write into the bootloader (unless
+  you throw in extra fruitsalad of options), so there is little risk
+  there.
+- EEPROM has around a 100000 write cycle.  You shouldn't rewrite the
+  firmware repeatedly and continually; that'll burn the EEPROM
+  eventually.
 ## NKRO Doesn't work
 First you have to compile frimware with this build option `NKRO_ENABLE` in **Makefile**.
 
 Try `Magic` **N** command(`LShift+RShift+N` by default) when **NKRO** still doesn't work. You can use this command to toggle between **NKRO** and **6KRO** mode temporarily. In some situations **NKRO** doesn't work you need to switch to **6KRO** mode, in particular when you are in BIOS.
 
-If your firmeare built with `BOOTMAGIC_ENABLE` you need to turn its switch on by `BootMagic` **N** command(`Space+N` by default). This setting is stored in EEPROM and keeped over power cycles.
+If your firmware built with `BOOTMAGIC_ENABLE` you need to turn its switch on by `BootMagic` **N** command(`Space+N` by default). This setting is stored in EEPROM and keeped over power cycles.
 
 https://github.com/tmk/tmk_keyboard#boot-magic-configuration---virtual-dip-switch
 
@@ -120,6 +159,7 @@ byte     Teensy(ATMega32u4)              byte     Teensy++(AT90SUB1286)
 And see this discussion for further reference.
 https://github.com/tmk/tmk_keyboard/issues/179
 
+If you are using a TeensyUSB, there is a [known bug](https://github.com/qmk/qmk_firmware/issues/164) in which the hardware reset button prevents the RESET key from working. Unplugging the keyboard and plugging it back in should resolve the problem.
 
 ## Special Extra key doesn't work(System, Audio control keys)
 You need to define `EXTRAKEY_ENABLE` in `rules.mk` to use them in QMK.