i2c fallback: add onekey scanner keymap

i2c scanner clone, configured for the fallback driver. ChibiOS only

keyboards/handwired/onekey/keymaps/i2c_scanner_fallback/config.h

@@ -0,0 +1,8 @@
+#pragma once
+
+// Default configuration using 100kHz on I2CD1
+#define SW_I2C_USE_I2C1 TRUE
+//#define I2C_CLOCK_FREQUENCY 100000
+//#define SW_I2C_USE_OSAL_DELAY TRUE
+//#define I2C1_SCL_PAL_MODE PAL_MODE_ALTERNATE_OPENDRAIN
+//#define I2C1_SDA_PAL_MODE PAL_MODE_ALTERNATE_OPENDRAIN

keyboards/handwired/onekey/keymaps/i2c_scanner_fallback/keymap.c

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+#include QMK_KEYBOARD_H
+
+#include "i2c_master.h"
+#include "debug.h"
+
+#define TIMEOUT 50
+
+// TODO: remove patch
+#ifdef PROTOCOL_CHIBIOS
+#    pragma message("ChibiOS is currently 'best effort' and might not report accurate results")
+
+#   if(SW_I2C_USE_OSAL_DELAY == FALSE)
+void i2c_sw_delay(void) {
+  // custom delay goes here
+}
+#   endif
+
+i2c_status_t i2c_start_bodge(uint8_t address, uint16_t timeout) {
+    i2c_start(address);
+
+    // except on ChibiOS where the only way is do do "something"
+    uint8_t data = 0;
+    return i2c_readReg(address, 0, &data, sizeof(data), TIMEOUT);
+}
+
+#    define i2c_start i2c_start_bodge
+#else
+#   pragma message("ChibiOS is currently the only supported platform")
+#endif
+
+const uint16_t PROGMEM keymaps[][MATRIX_ROWS][MATRIX_COLS] = {
+    LAYOUT_ortho_1x1(KC_A)
+};
+
+void do_scan(void) {
+    uint8_t nDevices = 0;
+
+    dprintf("Scanning...\n");
+
+    for (uint8_t address = 1; address < 127; address++) {
+        // The i2c_scanner uses the return value of
+        // i2c_start to see if a device did acknowledge to the address.
+        i2c_status_t error = i2c_start(address << 1, TIMEOUT);
+        if (error == I2C_STATUS_SUCCESS) {
+            i2c_stop();
+            dprintf("  I2C device found at address 0x%02X\n", address);
+            nDevices++;
+        } else {
+            // dprintf("  Unknown error (%u) at address 0x%02X\n", error, address);
+        }
+    }
+
+    if (nDevices == 0)
+        dprintf("No I2C devices found\n");
+    else
+        dprintf("done\n");
+}
+
+uint16_t scan_timer = 0;
+
+void matrix_scan_user(void) {
+    if (timer_elapsed(scan_timer) > 5000) {
+        do_scan();
+        scan_timer = timer_read();
+    }
+}
+
+void keyboard_post_init_user(void) {
+    debug_enable = true;
+    debug_matrix = true;
+
+    i2c_init();
+    scan_timer = timer_read();
+}

keyboards/handwired/onekey/keymaps/i2c_scanner_fallback/readme.md

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+# i2c_scanner_fallback
+
+Aiming to provide a more qmk friendly version of <https://playground.arduino.cc/Main/I2cScanner/>
+
+> This very simple ~~sketch~~ keymap scans the I2C-bus for devices. If a device is found, it is reported to the ~~Arduino serial monitor~~ console.
+
+ChibiOS only software bitbang using the I2C Fallback driver.
+
+## Flashing
+
+Pick a target that is aligned to the MCU you want to test:
+
+```console
+# ChibiOS is currently the only supported platform
+make handwired/onekey/proton_c:i2c_scanner:flash
+```
+
+others might work with additional configuration.
+
+## Usage
+
+Output is viewable through a compatible tool <https://docs.qmk.fm/#/newbs_testing_debugging?id=debugging-tools>.
+
+You can change the wires, and plug-in I2C devices while the i2c_scanner is running.
+
+The output of the console will look like this:
+
+```
+Listening:
+Scanning...
+  I2C device found at address 0x20
+done
+```

keyboards/handwired/onekey/keymaps/i2c_scanner_fallback/rules.mk

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+CONSOLE_ENABLE = yes
+
+I2C_DRIVER_REQUIRED = yes
+USE_HAL_I2C_FALLBACK = yes