Refactor steno and add `STENO_PROTOCOL = [all|txbolt|geminipr]` (#17065)

* Refactor steno into STENO_ENABLE_[ALL|GEMINI|BOLT]

* Update stenography documentation

* STENO_ENABLE_TXBOLT → STENO_ENABLE_BOLT

TXBOLT is a better name but BOLT is more consistent with the
pre-existing TX Bolt related constants, which all drop the "TX " prefix

* Comments

* STENO_ENABLE_[GEMINI|BOLT|ALL] → STENO_PROTOCOL = [geminipr|txbolt|all]

* Add note on lacking V-USB support

* Clear chord at the end of the switch(mode){send_steno_chord} block

* Return true if NOEVENT

* update_chord_xxx → add_xxx_key_to_chord

* Enable the defines for all the protocols if STENO_PROTOCOL = all

* Mention how to use `steno_set_mode`

* Set the default steno protocol to "all"

This is done so that existing keymaps invoking `steno_set_mode` don't
all suddenly break

* Add data driver equivalents for stenography feature

* Document format of serial steno packets

(Thanks dnaq)

* Add missing comma

9 files changed, 349 insertions, 179 deletions

diff --git a/builddefs/common_features.mk b/builddefs/common_features.mk
index 83505596d2..b9ee0a30a7 100644
--- a/builddefs/common_features.mk
+++ b/builddefs/common_features.mk
@@ -92,10 +92,29 @@ ifeq ($(MUSIC_ENABLE), yes)
     SRC += $(QUANTUM_DIR)/process_keycode/process_music.c
 endif
 
+VALID_STENO_PROTOCOL_TYPES := geminipr txbolt all
+STENO_PROTOCOL ?= all
 ifeq ($(strip $(STENO_ENABLE)), yes)
-    OPT_DEFS += -DSTENO_ENABLE
-    VIRTSER_ENABLE ?= yes
-    SRC += $(QUANTUM_DIR)/process_keycode/process_steno.c
+    ifeq ($(filter $(STENO_PROTOCOL),$(VALID_STENO_PROTOCOL_TYPES)),)
+        $(call CATASTROPHIC_ERROR,Invalid STENO_PROTOCOL,STENO_PROTOCOL="$(STENO_PROTOCOL)" is not a valid stenography protocol)
+    else
+        OPT_DEFS += -DSTENO_ENABLE
+        VIRTSER_ENABLE ?= yes
+
+        ifeq ($(strip $(STENO_PROTOCOL)), geminipr)
+            OPT_DEFS += -DSTENO_ENABLE_GEMINI
+        endif
+        ifeq ($(strip $(STENO_PROTOCOL)), txbolt)
+            OPT_DEFS += -DSTENO_ENABLE_BOLT
+        endif
+        ifeq ($(strip $(STENO_PROTOCOL)), all)
+            OPT_DEFS += -DSTENO_ENABLE_ALL
+            OPT_DEFS += -DSTENO_ENABLE_GEMINI
+            OPT_DEFS += -DSTENO_ENABLE_BOLT
+        endif
+
+        SRC += $(QUANTUM_DIR)/process_keycode/process_steno.c
+    endif
 endif
 
 ifeq ($(strip $(VIRTSER_ENABLE)), yes)
diff --git a/builddefs/show_options.mk b/builddefs/show_options.mk
index 1c1c189f27..98537e6da2 100644
--- a/builddefs/show_options.mk
+++ b/builddefs/show_options.mk
@@ -45,6 +45,7 @@ OTHER_OPTION_NAMES = \
   LEADER_ENABLE \
   PRINTING_ENABLE \
   STENO_ENABLE \
+  STENO_PROTOCOL \
   TAP_DANCE_ENABLE \
   VIRTSER_ENABLE \
   OLED_ENABLE \
diff --git a/data/mappings/info_rules.json b/data/mappings/info_rules.json
index 5cdae962a5..279b5ac213 100644
--- a/data/mappings/info_rules.json
+++ b/data/mappings/info_rules.json
@@ -28,6 +28,8 @@
     "SPLIT_KEYBOARD": {"info_key": "split.enabled", "value_type": "bool"},
     "SPLIT_TRANSPORT": {"info_key": "split.transport.protocol", "to_c": false},
     "WAIT_FOR_USB": {"info_key": "usb.wait_for", "value_type": "bool"},
+    "STENO_ENABLE": {"info_key": "stenography.enabled", "value_type": "bool"},
+    "STENO_PROTOCOL": {"info_key": "stenography.protocol"},
 
     # Items we want flagged in lint
     "CTPC": {"info_key": "_deprecated.ctpc", "deprecated": true},
diff --git a/data/schemas/keyboard.jsonschema b/data/schemas/keyboard.jsonschema
index 8d9fc4754d..ec5377b3b3 100644
--- a/data/schemas/keyboard.jsonschema
+++ b/data/schemas/keyboard.jsonschema
@@ -361,6 +361,17 @@
                 }
             }
         },
+        "stenography": {
+            "type": "object",
+            "additionalProperties": false,
+            "properties": {
+                "enabled": {"type": "boolean"},
+                "protocol": {
+                    "type": "string",
+                    "enum": ["all", "geminipr", "txbolt"]
+                }
+            }
+        },
         "split": {
             "type": "object",
             "additionalProperties": false,
diff --git a/docs/feature_stenography.md b/docs/feature_stenography.md
index 2b52bb17a6..e13fe845c5 100644
--- a/docs/feature_stenography.md
+++ b/docs/feature_stenography.md
@@ -8,46 +8,107 @@ The [Open Steno Project](https://www.openstenoproject.org/) has built an open-so
 
 Plover can work with any standard QWERTY keyboard, although it is more efficient if the keyboard supports NKRO (n-key rollover) to allow Plover to see all the pressed keys at once. An example keymap for Plover can be found in `planck/keymaps/default`. Switching to the `PLOVER` layer adjusts the position of the keyboard to support the number bar.
 
-To use Plover with QMK just enable NKRO and optionally adjust your layout if you have anything other than a standard layout. You may also want to purchase some steno-friendly keycaps to make it easier to hit multiple keys.
+To enable NKRO, add `NKRO_ENABLE = yes` in your `rules.mk` and make sure to press `NK_ON` to turn it on because `NKRO_ENABLE = yes` merely adds the possibility of switching to NKRO mode but it doesn't automatically switch to it. If you want to automatically switch, add `#define FORCE_NKRO` in your `config.h`.
+
+You may also need to adjust your layout, either in QMK or in Plover, if you have anything other than a standard layout. You may also want to purchase some steno-friendly keycaps to make it easier to hit multiple keys.
 
 ## Plover with Steno Protocol :id=plover-with-steno-protocol
 
-Plover also understands the language of several steno machines. QMK can speak a couple of these languages, TX Bolt and GeminiPR. An example layout can be found in `planck/keymaps/steno`.
+Plover also understands the language of several steno machines. QMK can speak a couple of these languages: TX Bolt and GeminiPR. An example layout can be found in `planck/keymaps/steno`.
+
+When QMK speaks to Plover over a steno protocol, Plover will not use the keyboard as input. This means that you can switch back and forth between a standard keyboard and your steno keyboard, or even switch layers from Plover to standard and back without needing to activate/deactivate Plover.
+
+In this mode, Plover expects to speak with a steno machine over a serial port so QMK will present itself to the operating system as a virtual serial port in addition to a keyboard.
 
-When QMK speaks to Plover over a steno protocol Plover will not use the keyboard as input. This means that you can switch back and forth between a standard keyboard and your steno keyboard, or even switch layers from Plover to standard and back without needing to activate/deactivate Plover.
+> Note: Due to hardware limitations, you might not be able to run both a virtual serial port and mouse emulation at the same time.
 
-In this mode Plover expects to speak with a steno machine over a serial port so QMK will present itself to the operating system as a virtual serial port in addition to a keyboard. By default QMK will speak the TX Bolt protocol but can be switched to GeminiPR; the last protocol used is stored in non-volatile memory so QMK will use the same protocol on restart.
+!> Serial stenography protocols are not supported on [V-USB keyboards](compatible_microcontrollers#atmel-avr).
 
-> Note: Due to hardware limitations you may not be able to run both a virtual serial port and mouse emulation at the same time.
+To enable stenography protocols, add the following lines to your `rules.mk`:
+```mk
+STENO_ENABLE = yes
+```
 
 ### TX Bolt :id=tx-bolt
 
-TX Bolt communicates the status of 24 keys over a very simple protocol in variable-sized (1-5 byte) packets.
+TX Bolt communicates the status of 24 keys over a simple protocol in variable-sized (1–4 bytes) packets.
 
-### GeminiPR :id=geminipr
+To select TX Bolt, add the following lines to your `rules.mk`:
+```mk
+STENO_ENABLE = yes
+STENO_PROTOCOL = txbolt
+```
 
-GeminiPR encodes 42 keys into a 6-byte packet. While TX Bolt contains everything that is necessary for standard stenography, GeminiPR opens up many more options, including supporting non-English theories.
+Each byte of the packet represents a different group of steno keys. Determining the group of a certain byte of the packet is done by checking the first two bits, the remaining bits are set if the corresponding steno key was pressed for the stroke. The last set of keys (as indicated by leading `11`) needs to keep track of less keys than there are bits so one of the bits is constantly 0.
 
-## Configuring QMK for Steno :id=configuring-qmk-for-steno
+The start of a new packet can be detected by comparing the group “ID” (the two MSBs) of the current byte to that of the previously received byte. If the group “ID” of the current byte is smaller or equal to that of the previous byte, it means that the current byte is the beginning of a new packet.
 
-Firstly, enable steno in your keymap's Makefile. You may also need disable mousekeys, extra keys, or another USB endpoint to prevent conflicts. The builtin USB stack for some processors only supports a certain number of USB endpoints and the virtual serial port needed for steno fills 3 of them.
+The format of TX Bolt packets is shown below.
+```
+00HWPKTS 01UE*OAR 10GLBPRF 110#ZDST
+```
+
+Examples of steno strokes and the associated packet:
+- `EUBG`    = `01110000 10101000`
+- `WAZ`     = `00010000 01000010 11001000`
+- `PHAPBGS` = `00101000 01000010 10101100 11000010`
+
+### GeminiPR :id=geminipr
+
+GeminiPR encodes 42 keys into a 6-byte packet. While TX Bolt contains everything that is necessary for standard stenography, GeminiPR opens up many more options, including differentiating between top and bottom `S-`, and supporting non-English theories.
 
-```make
+To select GeminiPR, add the following lines to your `rules.mk`:
+```mk
 STENO_ENABLE = yes
-MOUSEKEY_ENABLE = no
+STENO_PROTOCOL = geminipr
 ```
 
-In your keymap create a new layer for Plover. You will need to include `keymap_steno.h`. See `planck/keymaps/steno/keymap.c` for an example. Remember to create a key to switch to the layer as well as a key for exiting the layer. If you would like to switch modes on the fly you can use the keycodes `QK_STENO_BOLT` and `QK_STENO_GEMINI`. If you only want to use one of the protocols you may set it up in your initialization function:
+All packets in the GeminiPR protocol consist of exactly six bytes, used as bit-arrays for different groups of keys. The beginning of a packet is indicated by setting the most significant bit (MSB) to 1 while setting the MSB of the remaining five bytes to 0.
 
-```c
-void eeconfig_init_user() {
-    steno_set_mode(STENO_MODE_GEMINI); // or STENO_MODE_BOLT
-}
+The format of GeminiPR packets is shown below.
+```
+1 Fn  #1  #2 #3 #4 #5   #6
+0 S1- S2- T- K- P- W-   H-
+0 R-  A-  O- *1 *2 res1 res2
+0 pwr *3  *4 -E -U -F   -R
+0 -P  -B  -L -G -T -S   -D
+0 #7  #8  #9 #A #B #C   -Z
 ```
 
-Once you have your keyboard flashed launch Plover. Click the 'Configure...' button. In the 'Machine' tab select the Stenotype Machine that corresponds to your desired protocol. Click the 'Configure...' button on this tab and enter the serial port or click 'Scan'. Baud rate is fine at 9600 (although you should be able to set as high as 115200 with no issues). Use the default settings for everything else (Data Bits: 8, Stop Bits: 1, Parity: N, no flow control).
+Examples of steno strokes and the associated packet:
+- `EUBG`    = `10000000 00000000 00000000 00001100 00101000 00000000`
+- `WAZ`     = `10000000 00000010 00100000 00000000 00000000 00000001`
+- `PHAPBGS` = `10000000 00000101 00100000 00000000 01101010 00000000`
 
-On the display tab click 'Open stroke display'. With Plover disabled you should be able to hit keys on your keyboard and see them show up in the stroke display window. Use this to make sure you have set up your keymap correctly. You are now ready to steno!
+### Switching protocols on the fly :id=switching-protocols-on-the-fly
+
+If you wish to switch the serial protocol used to transfer the steno chords without having to recompile your keyboard firmware every time, you can press the `QK_STENO_BOLT` and `QK_STENO_GEMINI` keycodes in order to switch protocols on the fly.
+
+To enable these special keycodes, add the following lines to your `rules.mk`:
+```mk
+STENO_ENABLE = yes
+STENO_PROTOCOL = all
+```
+
+If you want to switch protocols programatically, as part of a custom macro for example, don't use `tap_code(QK_STENO_*)`, as `tap_code` only supports [basic keycodes](keycodes_basic). Instead, you should use `steno_set_mode(STENO_MODE_*)`, whose valid arguments are `STENO_MODE_BOLT` and `STENO_MODE_GEMINI`.
+
+The default protocol is Gemini PR but the last protocol used is stored in non-volatile memory so QMK will remember your choice between reboots of your keyboard — assuming that your keyboard features (emulated) EEPROM.
+
+Naturally, this option takes the most amount of firmware space as it needs to compile the code for all the available stenography protocols. In most cases, compiling a single stenography protocol is sufficient.
+
+The default value for `STENO_PROTOCOL` is `all`.
+
+## Configuring QMK for Steno :id=configuring-qmk-for-steno
+
+After enabling stenography and optionally selecting a protocol, you may also need disable mouse keys, extra keys, or another USB endpoint to prevent conflicts. The builtin USB stack for some processors only supports a certain number of USB endpoints and the virtual serial port needed for steno fills 3 of them.
+
+!> If you had *explicitly* set `VIRSTER_ENABLE = no`, none of the serial stenography protocols (GeminiPR, TX Bolt) will work properly. You are expected to either set it to `yes`, remove the line from your `rules.mk` or send the steno chords yourself in an alternative way using the [provided interceptable hooks](#interfacing-with-the-code).
+
+In your keymap, create a new layer for Plover, that you can fill in with the [steno keycodes](#keycode-reference) (you will need to include `keymap_steno.h`, see `planck/keymaps/steno/keymap.c` for an example). Remember to create a key to switch to the layer as well as a key for exiting the layer.
+
+Once you have your keyboard flashed, launch Plover. Click the 'Configure...' button. In the 'Machine' tab, select the Stenotype Machine that corresponds to your desired protocol. Click the 'Configure...' button on this tab and enter the serial port or click 'Scan'. Baud rate is fine at 9600 (although you should be able to set as high as 115200 with no issues). Use the default settings for everything else (Data Bits: 8, Stop Bits: 1, Parity: N, no flow control).
+
+To test your keymap, you can chord keys on your keyboard and either look at the output of the 'paper tape' (Tools > Paper Tape) or that of the 'layout display' (Tools > Layout Display). If your strokes correctly show up, you are now ready to steno!
 
 ## Learning Stenography :id=learning-stenography
 
@@ -60,7 +121,7 @@ On the display tab click 'Open stroke display'. With Plover disabled you should
 The steno code has three interceptable hooks. If you define these functions, they will be called at certain points in processing; if they return true, processing continues, otherwise it's assumed you handled things.
 
 ```c
-bool send_steno_chord_user(steno_mode_t mode, uint8_t chord[6]);
+bool send_steno_chord_user(steno_mode_t mode, uint8_t chord[MAX_STROKE_SIZE]);
 ```
 
 This function is called when a chord is about to be sent. Mode will be one of `STENO_MODE_BOLT` or `STENO_MODE_GEMINI`. This represents the actual chord that would be sent via whichever protocol. You can modify the chord provided to alter what gets sent. Remember to return true if you want the regular sending process to happen.
@@ -72,15 +133,23 @@ bool process_steno_user(uint16_t keycode, keyrecord_t *record) { return true; }
 This function is called when a keypress has come in, before it is processed. The keycode should be one of `QK_STENO_BOLT`, `QK_STENO_GEMINI`, or one of the `STN_*` key values.
 
 ```c
-bool postprocess_steno_user(uint16_t keycode, keyrecord_t *record, steno_mode_t mode, uint8_t chord[6], int8_t pressed);
+bool postprocess_steno_user(uint16_t keycode, keyrecord_t *record, steno_mode_t mode, uint8_t chord[MAX_STROKE_SIZE], int8_t n_pressed_keys);
 ```
 
-This function is called after a key has been processed, but before any decision about whether or not to send a chord. If `IS_PRESSED(record->event)` is false, and `pressed` is 0 or 1, the chord will be sent shortly, but has not yet been sent. This is where to put hooks for things like, say, live displays of steno chords or keys.
+This function is called after a key has been processed, but before any decision about whether or not to send a chord. This is where to put hooks for things like, say, live displays of steno chords or keys.
+
+If `IS_PRESSED(record->event)` is false, and `n_pressed_keys` is 0 or 1, the chord will be sent shortly, but has not yet been sent. This relieves you of the need of keeping track of where a packet ends and another begins.
+
+The `chord` argument contains the packet of the current chord as specified by the protocol in use. This is *NOT* simply a list of chorded steno keys of the form `[STN_E, STN_U, STN_BR, STN_GR]`. Refer to the appropriate protocol section of this document to learn more about the format of the packets in your steno protocol/mode of choice.
 
+The `n_pressed_keys` argument is the number of physical keys actually being held down.
+This is not always equal to the number of bits set to 1 (aka the [Hamming weight](https://en.wikipedia.org/wiki/Hamming_weight)) in `chord` because it is possible to simultaneously press down four keys, then release three of those four keys and then press yet another key while the fourth finger is still holding down its key.
+At the end of this scenario given as an example, `chord` would have five bits set to 1 but
+`n_pressed_keys` would be set to 2 because there are only two keys currently being pressed down.
 
 ## Keycode Reference :id=keycode-reference
 
-As defined in `keymap_steno.h`.
+You must include `keymap_steno.h` to your `keymap.c` with `#include "keymap_steno.h"` before you can use these keycodes
 
 > Note: TX Bolt does not support the full set of keys. The TX Bolt implementation in QMK will map the GeminiPR keys to the nearest TX Bolt key so that one key map will work for both.
 
@@ -124,10 +193,10 @@ As defined in `keymap_steno.h`.
 |`STN_SR`|`STN_SR`| `-S`|
 |`STN_DR`|`STN_DR`| `-D`|
 |`STN_ZR`|`STN_ZR`| `-Z`|
-|`STN_FN`|| (GeminiPR only)|
-|`STN_RES1`||(GeminiPR only)|
-|`STN_RES2`||(GeminiPR only)|
-|`STN_PWR`||(GeminiPR only)|
+|`STN_FN`|| (Function)|
+|`STN_RES1`||(Reset 1)|
+|`STN_RES2`||(Reset 2)|
+|`STN_PWR`||(Power)|
 
 If you do not want to hit two keys with one finger combined keycodes can be used. These are also defined in `keymap_steno.h`, and causes both keys to be reported as pressed or released. To use these keycodes define `STENO_COMBINEDMAP` in your `config.h` file.
 
diff --git a/quantum/keyboard.c b/quantum/keyboard.c
index a65f9d6d18..8273299a9a 100644
--- a/quantum/keyboard.c
+++ b/quantum/keyboard.c
@@ -381,7 +381,7 @@ void keyboard_init(void) {
 #ifdef ENCODER_ENABLE
     encoder_init();
 #endif
-#ifdef STENO_ENABLE
+#ifdef STENO_ENABLE_ALL
     steno_init();
 #endif
 #ifdef POINTING_DEVICE_ENABLE
diff --git a/quantum/keymap_extras/keymap_steno.h b/quantum/keymap_extras/keymap_steno.h
index e888ccd643..07d96b7465 100644
--- a/quantum/keymap_extras/keymap_steno.h
+++ b/quantum/keymap_extras/keymap_steno.h
@@ -89,3 +89,31 @@ enum steno_combined_keycodes {
     STN_COMB_MAX = STN_EU,
 };
 #endif
+
+#ifdef STENO_ENABLE_BOLT
+// TxBolt Codes
+#    define TXB_NUL 0
+#    define TXB_S_L 0b00000001
+#    define TXB_T_L 0b00000010
+#    define TXB_K_L 0b00000100
+#    define TXB_P_L 0b00001000
+#    define TXB_W_L 0b00010000
+#    define TXB_H_L 0b00100000
+#    define TXB_R_L 0b01000001
+#    define TXB_A_L 0b01000010
+#    define TXB_O_L 0b01000100
+#    define TXB_STR 0b01001000
+#    define TXB_E_R 0b01010000
+#    define TXB_U_R 0b01100000
+#    define TXB_F_R 0b10000001
+#    define TXB_R_R 0b10000010
+#    define TXB_P_R 0b10000100
+#    define TXB_B_R 0b10001000
+#    define TXB_L_R 0b10010000
+#    define TXB_G_R 0b10100000
+#    define TXB_T_R 0b11000001
+#    define TXB_S_R 0b11000010
+#    define TXB_D_R 0b11000100
+#    define TXB_Z_R 0b11001000
+#    define TXB_NUM 0b11010000
+#endif // STENO_ENABLE_BOLT
diff --git a/quantum/process_keycode/process_steno.c b/quantum/process_keycode/process_steno.c
index 12ee898212..20b8b9db4b 100644
--- a/quantum/process_keycode/process_steno.c
+++ b/quantum/process_keycode/process_steno.c
@@ -1,4 +1,4 @@
-/* Copyright 2017 Joseph Wasson
+/* Copyright 2017, 2022 Joseph Wasson, Vladislav Kucheriavykh
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -15,77 +15,118 @@
  */
 #include "process_steno.h"
 #include "quantum_keycodes.h"
-#include "eeprom.h"
 #include "keymap_steno.h"
-#include "virtser.h"
 #include <string.h>
+#ifdef VIRTSER_ENABLE
+#    include "virtser.h"
+#endif
+#ifdef STENO_ENABLE_ALL
+#    include "eeprom.h"
+#endif
 
-// TxBolt Codes
-#define TXB_NUL 0
-#define TXB_S_L 0b00000001
-#define TXB_T_L 0b00000010
-#define TXB_K_L 0b00000100
-#define TXB_P_L 0b00001000
-#define TXB_W_L 0b00010000
-#define TXB_H_L 0b00100000
-#define TXB_R_L 0b01000001
-#define TXB_A_L 0b01000010
-#define TXB_O_L 0b01000100
-#define TXB_STR 0b01001000
-#define TXB_E_R 0b01010000
-#define TXB_U_R 0b01100000
-#define TXB_F_R 0b10000001
-#define TXB_R_R 0b10000010
-#define TXB_P_R 0b10000100
-#define TXB_B_R 0b10001000
-#define TXB_L_R 0b10010000
-#define TXB_G_R 0b10100000
-#define TXB_T_R 0b11000001
-#define TXB_S_R 0b11000010
-#define TXB_D_R 0b11000100
-#define TXB_Z_R 0b11001000
-#define TXB_NUM 0b11010000
-
-#define TXB_GRP0 0b00000000
-#define TXB_GRP1 0b01000000
-#define TXB_GRP2 0b10000000
-#define TXB_GRP3 0b11000000
-#define TXB_GRPMASK 0b11000000
-
-#define TXB_GET_GROUP(code) ((code & TXB_GRPMASK) >> 6)
-
-#define BOLT_STATE_SIZE 4
-#define GEMINI_STATE_SIZE 6
-#define MAX_STATE_SIZE GEMINI_STATE_SIZE
-
-static uint8_t      state[MAX_STATE_SIZE] = {0};
-static uint8_t      chord[MAX_STATE_SIZE] = {0};
-static int8_t       pressed               = 0;
+// All steno keys that have been pressed to form this chord,
+// stored in MAX_STROKE_SIZE groups of 8-bit arrays.
+static uint8_t chord[MAX_STROKE_SIZE] = {0};
+// The number of physical keys actually being held down.
+// This is not always equal to the number of 1 bits in `chord` because it is possible to
+// simultaneously press down four keys, then release three of those four keys and then press yet
+// another key while the fourth finger is still holding down its key.
+// At the end of this scenario given as an example, `chord` would have five bits set to 1 but
+// `n_pressed_keys` would be set to 2 because there are only two keys currently being pressed down.
+static int8_t n_pressed_keys = 0;
+
+#ifdef STENO_ENABLE_ALL
 static steno_mode_t mode;
-
-static const uint8_t boltmap[64] PROGMEM = {TXB_NUL, TXB_NUM, TXB_NUM, TXB_NUM, TXB_NUM, TXB_NUM, TXB_NUM, TXB_S_L, TXB_S_L, TXB_T_L, TXB_K_L, TXB_P_L, TXB_W_L, TXB_H_L, TXB_R_L, TXB_A_L, TXB_O_L, TXB_STR, TXB_STR, TXB_NUL, TXB_NUL, TXB_NUL, TXB_STR, TXB_STR, TXB_E_R, TXB_U_R, TXB_F_R, TXB_R_R, TXB_P_R, TXB_B_R, TXB_L_R, TXB_G_R, TXB_T_R, TXB_S_R, TXB_D_R, TXB_NUM, TXB_NUM, TXB_NUM, TXB_NUM, TXB_NUM, TXB_NUM, TXB_Z_R};
-
-#ifdef STENO_COMBINEDMAP
-/* Used to look up when pressing the middle row key to combine two consonant or vowel keys */
-static const uint16_t combinedmap_first[] PROGMEM  = {STN_S1, STN_TL, STN_PL, STN_HL, STN_FR, STN_PR, STN_LR, STN_TR, STN_DR, STN_A, STN_E};
-static const uint16_t combinedmap_second[] PROGMEM = {STN_S2, STN_KL, STN_WL, STN_RL, STN_RR, STN_BR, STN_GR, STN_SR, STN_ZR, STN_O, STN_U};
+#elif defined(STENO_ENABLE_GEMINI)
+static const steno_mode_t mode = STENO_MODE_GEMINI;
+#elif defined(STENO_ENABLE_BOLT)
+static const steno_mode_t mode = STENO_MODE_BOLT;
 #endif
 
-static void steno_clear_state(void) {
-    memset(state, 0, sizeof(state));
+static inline void steno_clear_chord(void) {
     memset(chord, 0, sizeof(chord));
 }
 
-static void send_steno_state(uint8_t size, bool send_empty) {
-    for (uint8_t i = 0; i < size; ++i) {
-        if (chord[i] || send_empty) {
-#ifdef VIRTSER_ENABLE
+#ifdef STENO_ENABLE_GEMINI
+
+#    ifdef VIRTSER_ENABLE
+void send_steno_chord_gemini(void) {
+    // Set MSB to 1 to indicate the start of packet
+    chord[0] |= 0x80;
+    for (uint8_t i = 0; i < GEMINI_STROKE_SIZE; ++i) {
+        virtser_send(chord[i]);
+    }
+}
+#    else
+#        pragma message "VIRTSER_ENABLE = yes is required for Gemini PR to work properly out of the box!"
+#    endif // VIRTSER_ENABLE
+
+/**
+ * @precondition: `key` is pressed
+ */
+bool add_gemini_key_to_chord(uint8_t key) {
+    // Although each group of the packet is 8 bits long, the MSB is reserved
+    // to indicate whether that byte is the first byte of the packet (MSB=1)
+    // or one of the remaining five bytes of the packet (MSB=0).
+    // As a consequence, only 7 out of the 8 bits are left to be used as a bit array
+    // for the steno keys of that group.
+    const int group_idx       = key / 7;
+    const int intra_group_idx = key - group_idx * 7;
+    // The 0th steno key of the group has bit=0b01000000, the 1st has bit=0b00100000, etc.
+    const uint8_t bit = 1 << (6 - intra_group_idx);
+    chord[group_idx] |= bit;
+    return false;
+}
+#endif // STENO_ENABLE_GEMINI
+
+#ifdef STENO_ENABLE_BOLT
+
+#    define TXB_GRP0 0b00000000
+#    define TXB_GRP1 0b01000000
+#    define TXB_GRP2 0b10000000
+#    define TXB_GRP3 0b11000000
+#    define TXB_GRPMASK 0b11000000
+
+#    define TXB_GET_GROUP(code) ((code & TXB_GRPMASK) >> 6)
+
+static const uint8_t boltmap[64] PROGMEM = {TXB_NUL, TXB_NUM, TXB_NUM, TXB_NUM, TXB_NUM, TXB_NUM, TXB_NUM, TXB_S_L, TXB_S_L, TXB_T_L, TXB_K_L, TXB_P_L, TXB_W_L, TXB_H_L, TXB_R_L, TXB_A_L, TXB_O_L, TXB_STR, TXB_STR, TXB_NUL, TXB_NUL, TXB_NUL, TXB_STR, TXB_STR, TXB_E_R, TXB_U_R, TXB_F_R, TXB_R_R, TXB_P_R, TXB_B_R, TXB_L_R, TXB_G_R, TXB_T_R, TXB_S_R, TXB_D_R, TXB_NUM, TXB_NUM, TXB_NUM, TXB_NUM, TXB_NUM, TXB_NUM, TXB_Z_R};
+
+#    ifdef VIRTSER_ENABLE
+static void send_steno_chord_bolt(void) {
+    for (uint8_t i = 0; i < BOLT_STROKE_SIZE; ++i) {
+        // TX Bolt uses variable length packets where each byte corresponds to a bit array of certain keys.
+        // If a user chorded the keys of the first group with keys of the last group, for example, there
+        // would be bytes of 0x00 in `chord` for the middle groups which we mustn't send.
+        if (chord[i]) {
             virtser_send(chord[i]);
-#endif
         }
     }
+    // Sending a null packet is not always necessary, but it is simpler and more reliable
+    // to unconditionally send it every time instead of keeping track of more states and
+    // creating more branches in the execution of the program.
+    virtser_send(0);
 }
+#    else
+#        pragma message "VIRTSER_ENABLE = yes is required for TX Bolt to work properly out of the box!"
+#    endif // VIRTSER_ENABLE
+
+/**
+ * @precondition: `key` is pressed
+ */
+static bool add_bolt_key_to_chord(uint8_t key) {
+    uint8_t boltcode = pgm_read_byte(boltmap + key);
+    chord[TXB_GET_GROUP(boltcode)] |= boltcode;
+    return false;
+}
+#endif // STENO_ENABLE_BOLT
+
+#ifdef STENO_COMBINEDMAP
+/* Used to look up when pressing the middle row key to combine two consonant or vowel keys */
+static const uint16_t combinedmap_first[] PROGMEM  = {STN_S1, STN_TL, STN_PL, STN_HL, STN_FR, STN_PR, STN_LR, STN_TR, STN_DR, STN_A, STN_E};
+static const uint16_t combinedmap_second[] PROGMEM = {STN_S2, STN_KL, STN_WL, STN_RL, STN_RR, STN_BR, STN_GR, STN_SR, STN_ZR, STN_O, STN_U};
+#endif
 
+#ifdef STENO_ENABLE_ALL
 void steno_init() {
     if (!eeconfig_is_enabled()) {
         eeconfig_init();
@@ -94,19 +135,20 @@ void steno_init() {
 }
 
 void steno_set_mode(steno_mode_t new_mode) {
-    steno_clear_state();
+    steno_clear_chord();
     mode = new_mode;
     eeprom_update_byte(EECONFIG_STENOMODE, mode);
 }
+#endif // STENO_ENABLE_ALL
 
 /* override to intercept chords right before they get sent.
  * return zero to suppress normal sending behavior.
  */
-__attribute__((weak)) bool send_steno_chord_user(steno_mode_t mode, uint8_t chord[6]) {
+__attribute__((weak)) bool send_steno_chord_user(steno_mode_t mode, uint8_t chord[MAX_STROKE_SIZE]) {
     return true;
 }
 
-__attribute__((weak)) bool postprocess_steno_user(uint16_t keycode, keyrecord_t *record, steno_mode_t mode, uint8_t chord[6], int8_t pressed) {
+__attribute__((weak)) bool postprocess_steno_user(uint16_t keycode, keyrecord_t *record, steno_mode_t mode, uint8_t chord[MAX_STROKE_SIZE], int8_t n_pressed_keys) {
     return true;
 }
 
@@ -114,108 +156,94 @@ __attribute__((weak)) bool process_steno_user(uint16_t keycode, keyrecord_t *rec
     return true;
 }
 
-static void send_steno_chord(void) {
-    if (send_steno_chord_user(mode, chord)) {
-        switch (mode) {
-            case STENO_MODE_BOLT:
-                send_steno_state(BOLT_STATE_SIZE, false);
-#ifdef VIRTSER_ENABLE
-                virtser_send(0); // terminating byte
-#endif
-                break;
-            case STENO_MODE_GEMINI:
-                chord[0] |= 0x80; // Indicate start of packet
-                send_steno_state(GEMINI_STATE_SIZE, true);
-                break;
-        }
+bool process_steno(uint16_t keycode, keyrecord_t *record) {
+    if (keycode < QK_STENO || keycode > QK_STENO_MAX) {
+        return true; // Not a steno key, pass it further along the chain
+        /*
+         * Clearing or sending the chord state is not necessary as we intentionally ignore whatever
+         * normal keyboard keys the user may have tapped while chording steno keys.
+         */
     }
-    steno_clear_state();
-}
-
-uint8_t *steno_get_state(void) {
-    return &state[0];
-}
-
-uint8_t *steno_get_chord(void) {
-    return &chord[0];
-}
-
-static bool update_state_bolt(uint8_t key, bool press) {
-    uint8_t boltcode = pgm_read_byte(boltmap + key);
-    if (press) {
-        state[TXB_GET_GROUP(boltcode)] |= boltcode;
-        chord[TXB_GET_GROUP(boltcode)] |= boltcode;
-    } else {
-        state[TXB_GET_GROUP(boltcode)] &= ~boltcode;
+    if (IS_NOEVENT(record->event)) {
+        return true;
     }
-    return false;
-}
-
-static bool update_state_gemini(uint8_t key, bool press) {
-    int     idx = key / 7;
-    uint8_t bit = 1 << (6 - (key % 7));
-    if (press) {
-        state[idx] |= bit;
-        chord[idx] |= bit;
-    } else {
-        state[idx] &= ~bit;
+    if (!process_steno_user(keycode, record)) {
+        return false; // User fully processed the steno key themselves
     }
-    return false;
-}
-
-bool process_steno(uint16_t keycode, keyrecord_t *record) {
     switch (keycode) {
+#ifdef STENO_ENABLE_ALL
         case QK_STENO_BOLT:
-            if (!process_steno_user(keycode, record)) {
-                return false;
-            }
             if (IS_PRESSED(record->event)) {
                 steno_set_mode(STENO_MODE_BOLT);
             }
             return false;
 
         case QK_STENO_GEMINI:
-            if (!process_steno_user(keycode, record)) {
-                return false;
-            }
             if (IS_PRESSED(record->event)) {
                 steno_set_mode(STENO_MODE_GEMINI);
             }
             return false;
+#endif // STENO_ENABLE_ALL
 
 #ifdef STENO_COMBINEDMAP
         case QK_STENO_COMB ... QK_STENO_COMB_MAX: {
-            uint8_t result;
-            result = process_steno(combinedmap_first[keycode - QK_STENO_COMB], record);
-            result &= process_steno(combinedmap_second[keycode - QK_STENO_COMB], record);
-            return result;
+            bool first_result  = process_steno(combinedmap_first[keycode - QK_STENO_COMB], record);
+            bool second_result = process_steno(combinedmap_second[keycode - QK_STENO_COMB], record);
+            return first_result && second_result;
         }
-#endif
+#endif // STENO_COMBINEDMAP
         case STN__MIN ... STN__MAX:
-            if (!process_steno_user(keycode, record)) {
-                return false;
-            }
-            switch (mode) {
-                case STENO_MODE_BOLT:
-                    update_state_bolt(keycode - QK_STENO, IS_PRESSED(record->event));
-                    break;
-                case STENO_MODE_GEMINI:
-                    update_state_gemini(keycode - QK_STENO, IS_PRESSED(record->event));
-                    break;
-            }
-            // allow postprocessing hooks
-            if (postprocess_steno_user(keycode, record, mode, chord, pressed)) {
-                if (IS_PRESSED(record->event)) {
-                    ++pressed;
-                } else {
-                    --pressed;
-                    if (pressed <= 0) {
-                        pressed = 0;
-                        send_steno_chord();
-                    }
+            if (IS_PRESSED(record->event)) {
+                n_pressed_keys++;
+                switch (mode) {
+#ifdef STENO_ENABLE_BOLT
+                    case STENO_MODE_BOLT:
+                        add_bolt_key_to_chord(keycode - QK_STENO);
+                        break;
+#endif // STENO_ENABLE_BOLT
+#ifdef STENO_ENABLE_GEMINI
+                    case STENO_MODE_GEMINI:
+                        add_gemini_key_to_chord(keycode - QK_STENO);
+                        break;
+#endif // STENO_ENABLE_GEMINI
+                    default:
+                        return false;
                 }
+                if (!postprocess_steno_user(keycode, record, mode, chord, n_pressed_keys)) {
+                    return false;
+                }
+            } else { // is released
+                n_pressed_keys--;
+                if (!postprocess_steno_user(keycode, record, mode, chord, n_pressed_keys)) {
+                    return false;
+                }
+                if (n_pressed_keys > 0) {
+                    // User hasn't released all keys yet,
+                    // so the chord cannot be sent
+                    return false;
+                }
+                n_pressed_keys = 0;
+                if (!send_steno_chord_user(mode, chord)) {
+                    steno_clear_chord();
+                    return false;
+                }
+                switch (mode) {
+#if defined(STENO_ENABLE_BOLT) && defined(VIRTSER_ENABLE)
+                    case STENO_MODE_BOLT:
+                        send_steno_chord_bolt();
+                        break;
+#endif // STENO_ENABLE_BOLT && VIRTSER_ENABLE
+#if defined(STENO_ENABLE_GEMINI) && defined(VIRTSER_ENABLE)
+                    case STENO_MODE_GEMINI:
+                        send_steno_chord_gemini();
+                        break;
+#endif // STENO_ENABLE_GEMINI && VIRTSER_ENABLE
+                    default:
+                        break;
+                }
+                steno_clear_chord();
             }
-            return false;
+            break;
     }
-    return true;
+    return false;
 }
diff --git a/quantum/process_keycode/process_steno.h b/quantum/process_keycode/process_steno.h
index d11fd40af0..68d6097b9b 100644
--- a/quantum/process_keycode/process_steno.h
+++ b/quantum/process_keycode/process_steno.h
@@ -18,10 +18,22 @@
 
 #include "quantum.h"
 
-typedef enum { STENO_MODE_BOLT, STENO_MODE_GEMINI } steno_mode_t;
+#define BOLT_STROKE_SIZE 4
+#define GEMINI_STROKE_SIZE 6
 
-bool     process_steno(uint16_t keycode, keyrecord_t *record);
-void     steno_init(void);
-void     steno_set_mode(steno_mode_t mode);
-uint8_t *steno_get_state(void);
-uint8_t *steno_get_chord(void);
+#ifdef STENO_ENABLE_GEMINI
+#    define MAX_STROKE_SIZE GEMINI_STROKE_SIZE
+#else
+#    define MAX_STROKE_SIZE BOLT_STROKE_SIZE
+#endif
+
+typedef enum {
+    STENO_MODE_GEMINI,
+    STENO_MODE_BOLT,
+} steno_mode_t;
+
+bool process_steno(uint16_t keycode, keyrecord_t *record);
+#ifdef STENO_ENABLE_ALL
+void steno_init(void);
+void steno_set_mode(steno_mode_t mode);
+#endif // STENO_ENABLE_ALL