Add rgeorge/model_c keyboard by rgeorge1926-oss · Pull Request #26341 · qmk/qmk_firmware

rgeorge1926-oss · 2026-07-18T15:45:45Z

Description

Adds the Model-C keyboard — a custom IBM Model M compatible keyboard controller using QMK firmware.

Hardware

ATmega32U4 (Arduino Pro Micro) microcontroller
Two MCP23S17 SPI port expanders for 8x16 matrix scanning
Standard IBM Model M connector pinout compatibility
Three status LEDs (caps lock, scroll lock, num lock)
German QWERTZ layout with umlaut support via unicode layer

Implementation

Uses CUSTOM_MATRIX=lite with MCP23S17 port expanders connected via hardware SPI. The matrix scanning uses high-impedance column deselection to avoid sneak paths in the diodeless matrix.

Checklist

I have read the Keyboard Templates and Keyboard Guidelines
This keyboard does not appear in the QMK Hardware Database
I have maintained a changelog
I have completed all of the primary items on the Keyboard Submission Checklist
I have tested the keyboard and it is working correctly
I have pointed the maintainer entry in the keyboard readme.md to myself and only myself

sigprof · 2026-07-18T16:43:45Z

This keyboard should be under ibm/model_m/ (see #14996 and other issues linked there).

Also https://github.com/rgeorge/model-c does not seem to be accessible at the moment.

sigprof · 2026-07-18T17:11:08Z

+/* Matrix pins are driven by MCP23S17 port expanders via SPI - NOT direct GPIO */
+#define MATRIX_ROW_PINS \
+    { NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN }
+#define MATRIX_COL_PINS \
+    { NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN }
+
+/* COL2ROW, ROW2COL */
+#define DIODE_DIRECTION ROW2COL
+


These definitions are not needed (only the default matrix implementation needs them, but your custom matrix implementation does not use them).

Suggested change

/* Matrix pins are driven by MCP23S17 port expanders via SPI - NOT direct GPIO */

#define MATRIX_ROW_PINS \

{ NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN }

#define MATRIX_COL_PINS \

{ NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN, NO_PIN }

/* COL2ROW, ROW2COL */

#define DIODE_DIRECTION ROW2COL

sigprof · 2026-07-18T17:12:47Z

+/* Bootmagic Lite config */
+#define BOOTMAGIC_LITE_ROW 0
+#define BOOTMAGIC_LITE_COLUMN 5
+


The bootmagic config should be moved to JSON (set bootmagic.matrix).

Suggested change

/* Bootmagic Lite config */

#define BOOTMAGIC_LITE_ROW 0

#define BOOTMAGIC_LITE_COLUMN 5

sigprof · 2026-07-18T17:13:49Z

+
+/* LED pins - active low (sinking current to VDD) */
+#define LED1_PIN E6 /* Arduino D7 -> PE6 -> QMK E6 */
+#define LED2_PIN B4 /* Arduino D8 -> PB4 -> QMK B4 */
+#define LED3_PIN B5 /* Arduino D9 -> PB5 -> QMK B5 */


LEDs also should be configured in JSON (indicators.{caps_lock,num_lock,scroll_lock,on_state}).

Suggested change

/* LED pins - active low (sinking current to VDD) */

#define LED1_PIN E6 /* Arduino D7 -> PE6 -> QMK E6 */

#define LED2_PIN B4 /* Arduino D8 -> PB4 -> QMK B4 */

#define LED3_PIN B5 /* Arduino D9 -> PB5 -> QMK B5 */

sigprof · 2026-07-18T17:18:10Z

+    "vid": "0x04D8",
+    "pid": "0xED10",


This VID belongs to Microchip Technology Inc.; did you actually request and receive a PID from them? If not, the common convention used in QMK is to select a random unregistered VID value above 0x4000 which does not collide with anything in https://yanfali.github.io/qmk_usb_usage/ and https://www.the-sz.com/products/usbid/, and any PID value you like. Alternatively, there are some places which can hand out presumably unique USB VID:PID combinations for Open Hardware projects.

sigprof · 2026-07-18T17:22:15Z

The custom matrix implementation should be placed in a file named matrix.c.

Any other custom code should be placed in a *.c file with exactly the same name as the last component of the keyboard name (for the currently used name it would be model_c.c, not model-c.c); this file should not be mentioned in SRC (it would be used automatically). However, you may not need such a file at all (the code which inits the matrix pins could be moved to matrix_init_custom(), and the custom LED code won't be needed if you move the LED pin definitions into JSON).

sigprof · 2026-07-18T17:38:55Z

+
+CUSTOM_MATRIX = lite
+
+SRC += model-c.c


Suggested change

SRC += model-c.c

SRC += matrix.c

The custom matrix implementation should be moved to matrix.c, and even if you end up needing <keyboard>.c, it does not need to be mentioned in SRC.

sigprof · 2026-07-18T17:44:08Z

https://docs.qmk.fm/pr_checklist#keyboard-prs:

default keymaps should be "pristine"

So you should not have your Unicode setup in the default keymap — just make a plain QWERTY keymap.

And also your LAYOUT macro included from model-c.h is completely wrong — you should use #include QMK_KEYBOARD_H to get the generated macro (which would expect key mappings in the same order as defined in JSON, which should roughly match the physical keyboard layout, not the electrical one).

sigprof · 2026-07-18T17:48:20Z

Use qmk format-json to reformat keyboard.json, so that the file (especially the layout section) would be more readable.

sigprof · 2026-07-18T17:54:54Z

+    "bootmagic": true,
+    "command": true,
+    "extrakey": true,
+    "ghost": false,


Suggested change

"ghost": false,

features.ghost does not exist, so this definition just does nothing. The proper JSON key is matrix_pins.ghost, and I suspect that you actually need to set it to true (because the ghosting behavior when pressing multiple keys at once would be present in a diodeless matrix; the high-impedance deselection which you use only avoids overloading the chip outputs when multiple outputs get connected together).

sigprof · 2026-07-18T17:56:34Z

+    "extrakey": true,
+    "ghost": false,
+    "mousekey": true,
+    "nkro": true


This is probably useless if your hardware is actually 2KRO.

drashna · 2026-07-19T06:44:30Z

+  "processor": "atmega32u4",
+  "bootloader": "caterina",


Suggested change

"processor": "atmega32u4",

"bootloader": "caterina",

"development_board": "promicro",

This will set the controller and bootloader, and setup compatibility with converters.

IBM Model M compatible keyboard controller using ATmega32U4 (Arduino Pro Micro) with two MCP23S17 SPI port expanders to scan the 8x16 key matrix.

…, name HAEN constant

zvecr

The folder structure here is incorrect. The files need to be inside a sub-folder of keyboards/ibm/model_m and the keymaps need to be within a keymaps folder.

zvecr · 2026-07-19T18:10:37Z

+// Custom Matrix Implementation
+//------------------------------------------------------------------------------
+
+void matrix_init_custom(void) {


Suggested change

void matrix_init_custom(void) {

void matrix_init_custom(void) {

// Initialize SPI master

spi_init();

// Set chip select pins as output

gpio_set_pin_output(MCP23S17_CS1_PIN);

gpio_set_pin_output(MCP23S17_CS2_PIN);

// Deselect both chips (active low, so write HIGH)

gpio_write_pin_high(MCP23S17_CS1_PIN);

gpio_write_pin_high(MCP23S17_CS2_PIN);

zvecr · 2026-07-19T18:11:01Z

+void keyboard_pre_init_kb(void) {
+    // Initialize SPI master
+    spi_init();
+
+    // Set chip select pins as output
+    gpio_set_pin_output(MCP23S17_CS1);
+    gpio_set_pin_output(MCP23S17_CS2);
+
+    // Deselect both chips (active low, so write HIGH)
+    gpio_write_pin_high(MCP23S17_CS1);
+    gpio_write_pin_high(MCP23S17_CS2);
+
+    keyboard_pre_init_user();
+}
+


Suggested change

void keyboard_pre_init_kb(void) {

// Initialize SPI master

spi_init();

// Set chip select pins as output

gpio_set_pin_output(MCP23S17_CS1);

gpio_set_pin_output(MCP23S17_CS2);

// Deselect both chips (active low, so write HIGH)

gpio_write_pin_high(MCP23S17_CS1);

gpio_write_pin_high(MCP23S17_CS2);

keyboard_pre_init_user();

}

zvecr · 2026-07-19T18:12:06Z

+#define MCP23S17_CS1_PIN C6 /* D5 -> PC6 (CS1 - Expander A for columns) */
+#define MCP23S17_CS2_PIN D7 /* D6 -> PD7 (CS2 - Expander B for rows) */


Doesnt really add value as the only file thats ever going to use it is the keyboards matrix.c

Suggested change

#define MCP23S17_CS1_PIN C6 /* D5 -> PC6 (CS1 - Expander A for columns) */

#define MCP23S17_CS2_PIN D7 /* D6 -> PD7 (CS2 - Expander B for rows) */

zvecr · 2026-07-19T18:17:16Z

+
+// MCP23S17 chip select pins (for two expanders)
+#define MCP23S17_CS1 (uint8_t) MCP23S17_CS1_PIN // CS for expander A (columns), address 0x01
+#define MCP23S17_CS2 (uint8_t) MCP23S17_CS2_PIN // CS for expander B (rows), address 0x00


Suggested change

#define MCP23S17_CS2 (uint8_t) MCP23S17_CS2_PIN // CS for expander B (rows), address 0x00

#define MCP23S17_CS1_PIN C6 /* D5 -> PC6 (CS1 - Expander A for columns) */

#define MCP23S17_CS2_PIN D7 /* D6 -> PD7 (CS2 - Expander B for rows) */

zvecr · 2026-07-19T18:17:30Z

+static void    mcp23s17_init_expander(uint8_t cs_pin, uint8_t addr, uint8_t iodir_a, uint8_t iodir_b);
+static void    mcp23s17_write_reg(uint8_t cs_pin, uint8_t addr, uint8_t reg_addr, uint8_t data);
+static uint8_t mcp23s17_read_reg(uint8_t cs_pin, uint8_t addr, uint8_t reg_addr);


Suggested change

static void mcp23s17_init_expander(uint8_t cs_pin, uint8_t addr, uint8_t iodir_a, uint8_t iodir_b);

static void mcp23s17_write_reg(uint8_t cs_pin, uint8_t addr, uint8_t reg_addr, uint8_t data);

static uint8_t mcp23s17_read_reg(uint8_t cs_pin, uint8_t addr, uint8_t reg_addr);

static void mcp23s17_init_expander(pin_t cs_pin, uint8_t addr, uint8_t iodir_a, uint8_t iodir_b);

static void mcp23s17_write_reg(pin_t cs_pin, uint8_t addr, uint8_t reg_addr, uint8_t data);

static uint8_t mcp23s17_read_reg(pin_t cs_pin, uint8_t addr, uint8_t reg_addr);

zvecr · 2026-07-19T18:19:01Z

+    mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_IODIRA, 0xFF);
+    mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_IODIRB, 0xFF);
+
+    if (col < 8) {
+        mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_GPIOA, ~(1 << col));
+        mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_IODIRA, ~(1 << col));
+    } else {
+        mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_GPIOB, ~(1 << (col - 8)));
+        mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_IODIRB, ~(1 << (col - 8)));


Suggested change

mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_IODIRA, 0xFF);

mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_IODIRB, 0xFF);

if (col < 8) {

mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_GPIOA, ~(1 << col));

mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_IODIRA, ~(1 << col));

} else {

mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_GPIOB, ~(1 << (col - 8)));

mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_IODIRB, ~(1 << (col - 8)));

mcp23s17_write_reg(MCP23S17_CS1_PIN, 0x01, MCP23S17_IODIRA, 0xFF);

mcp23s17_write_reg(MCP23S17_CS1_PIN, 0x01, MCP23S17_IODIRB, 0xFF);

if (col < 8) {

mcp23s17_write_reg(MCP23S17_CS1_PIN, 0x01, MCP23S17_GPIOA, ~(1 << col));

mcp23s17_write_reg(MCP23S17_CS1_PIN, 0x01, MCP23S17_IODIRA, ~(1 << col));

} else {

mcp23s17_write_reg(MCP23S17_CS1_PIN, 0x01, MCP23S17_GPIOB, ~(1 << (col - 8)));

mcp23s17_write_reg(MCP23S17_CS1_PIN, 0x01, MCP23S17_IODIRB, ~(1 << (col - 8)));

zvecr · 2026-07-19T18:19:48Z

+    mcp23s17_write_reg(MCP23S17_CS2, 0x00, MCP23S17_IOCON, MCP23S17_IOCON_HAEN);
+    mcp23s17_write_reg(MCP23S17_CS1, 0x00, MCP23S17_IOCON, MCP23S17_IOCON_HAEN);
+
+    // Expander B (CS2, addr 0x00) - Short 8-pin connector (Rows), all inputs
+    mcp23s17_init_expander(MCP23S17_CS2, 0x00, 0xFF, 0xFF);
+    // Enable pull-ups on row expander GPA0-GPA7
+    mcp23s17_write_reg(MCP23S17_CS2, 0x00, MCP23S17_GPPUA, 0xFF);
+
+    // Expander A (CS1, addr 0x01) - Long 16-pin connector (Columns)
+    // First init as all outputs with OLAT=0xFF (HIGH) so the output latches are set,
+    // then switch to all inputs (high-impedance) for diodeless-safe scanning.
+    mcp23s17_init_expander(MCP23S17_CS1, 0x01, 0x00, 0x00);
+    mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_IODIRA, 0xFF);
+    mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_IODIRB, 0xFF);


Suggested change

mcp23s17_write_reg(MCP23S17_CS2, 0x00, MCP23S17_IOCON, MCP23S17_IOCON_HAEN);

mcp23s17_write_reg(MCP23S17_CS1, 0x00, MCP23S17_IOCON, MCP23S17_IOCON_HAEN);

// Expander B (CS2, addr 0x00) - Short 8-pin connector (Rows), all inputs

mcp23s17_init_expander(MCP23S17_CS2, 0x00, 0xFF, 0xFF);

// Enable pull-ups on row expander GPA0-GPA7

mcp23s17_write_reg(MCP23S17_CS2, 0x00, MCP23S17_GPPUA, 0xFF);

// Expander A (CS1, addr 0x01) - Long 16-pin connector (Columns)

// First init as all outputs with OLAT=0xFF (HIGH) so the output latches are set,

// then switch to all inputs (high-impedance) for diodeless-safe scanning.

mcp23s17_init_expander(MCP23S17_CS1, 0x01, 0x00, 0x00);

mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_IODIRA, 0xFF);

mcp23s17_write_reg(MCP23S17_CS1, 0x01, MCP23S17_IODIRB, 0xFF);

mcp23s17_write_reg(MCP23S17_CS2_PIN, 0x00, MCP23S17_IOCON, MCP23S17_IOCON_HAEN);

mcp23s17_write_reg(MCP23S17_CS1_PIN, 0x00, MCP23S17_IOCON, MCP23S17_IOCON_HAEN);

// Expander B (CS2, addr 0x00) - Short 8-pin connector (Rows), all inputs

mcp23s17_init_expander(MCP23S17_CS2_PIN, 0x00, 0xFF, 0xFF);

// Enable pull-ups on row expander GPA0-GPA7

mcp23s17_write_reg(MCP23S17_CS2_PIN, 0x00, MCP23S17_GPPUA, 0xFF);

// Expander A (CS1, addr 0x01) - Long 16-pin connector (Columns)

// First init as all outputs with OLAT=0xFF (HIGH) so the output latches are set,

// then switch to all inputs (high-impedance) for diodeless-safe scanning.

mcp23s17_init_expander(MCP23S17_CS1_PIN, 0x01, 0x00, 0x00);

mcp23s17_write_reg(MCP23S17_CS1_PIN, 0x01, MCP23S17_IODIRA, 0xFF);

mcp23s17_write_reg(MCP23S17_CS1_PIN, 0x01, MCP23S17_IODIRB, 0xFF);

zvecr · 2026-07-19T18:20:51Z

This file should be removed.

zvecr · 2026-07-19T18:21:00Z

This file should be removed.

zvecr · 2026-07-19T18:21:20Z

This file should be removed.

github-actions Bot added keyboard keymap labels Jul 18, 2026

rgeorge1926-oss force-pushed the add-model-c-keyboard branch 3 times, most recently from 6dbbe29 to b09c38e Compare July 18, 2026 16:31

sigprof requested changes Jul 18, 2026

View reviewed changes

drashna reviewed Jul 19, 2026

View reviewed changes

Add ibm/model_m keyboard

27367e2

IBM Model M compatible keyboard controller using ATmega32U4 (Arduino Pro Micro) with two MCP23S17 SPI port expanders to scan the 8x16 key matrix.

rgeorge1926-oss force-pushed the add-model-c-keyboard branch from b09c38e to 27367e2 Compare July 19, 2026 15:21

richard added 3 commits July 19, 2026 17:51

Fix capslayer readme: add missing trailing newline

6b086e6

Rename keymaps to rgeorge and add README with PCB hardware link

8051308

Address remaining review feedback: remove redundant SPI pins, fix VID…

1690888

…, name HAEN constant

zvecr requested changes Jul 19, 2026

View reviewed changes

	/* Bootmagic Lite config */
	#define BOOTMAGIC_LITE_ROW 0
	#define BOOTMAGIC_LITE_COLUMN 5

	"processor": "atmega32u4",
	"bootloader": "caterina",
	"development_board": "promicro",

		#define MCP23S17_CS1_PIN C6 /* D5 -> PC6 (CS1 - Expander A for columns) */
		#define MCP23S17_CS2_PIN D7 /* D6 -> PD7 (CS2 - Expander B for rows) */

	#define MCP23S17_CS2 (uint8_t) MCP23S17_CS2_PIN // CS for expander B (rows), address 0x00
	#define MCP23S17_CS1_PIN C6 /* D5 -> PC6 (CS1 - Expander A for columns) */
	#define MCP23S17_CS2_PIN D7 /* D6 -> PD7 (CS2 - Expander B for rows) */

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Description

Hardware

Implementation

Checklist

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sigprof commented Jul 18, 2026

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rgeorge1926-oss commented Jul 18, 2026 •

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