Add CRC8 calculation subsystem to quantum

* Intended usage is data validation in split transport code.
* Default space efficient algorithm.
* Opt-in fast table based algorithmn with #define CRC8_USE_TABLE switch.
* Define switches for size and speed optimized versions, the default is size
  optimized by using uint_least8_t as datatype for calculations.
  * #define CRC8_OPTIMIZE_SPEED uses uint_fast8_t as datatype for
    calculations, this only affects 32-bit Archs like ARM and RISC-V.
* Placeholder crc_init() function for hardware backed crc calculation,
  not implemented yet.

common_features.mk

@@ -519,6 +519,7 @@ endif
 ifeq ($(strip $(SPLIT_KEYBOARD)), yes)
     POST_CONFIG_H += $(QUANTUM_DIR)/split_common/post_config.h
     OPT_DEFS += -DSPLIT_KEYBOARD
+    CRC_ENABLE := yes
 
     # Include files used by all split keyboards
     QUANTUM_SRC += $(QUANTUM_DIR)/split_common/split_util.c
@@ -546,6 +547,11 @@ ifeq ($(strip $(SPLIT_KEYBOARD)), yes)
     COMMON_VPATH += $(QUANTUM_PATH)/split_common
 endif
 
+ifeq ($(strip $(CRC_ENABLE)), yes)
+    OPT_DEFS += -DCRC_ENABLE
+    QUANTUM_LIB_SRC += crc.c
+endif
+
 HAPTIC_ENABLE ?= no
 ifneq ($(strip $(HAPTIC_ENABLE)),no)
     COMMON_VPATH += $(DRIVER_PATH)/haptic

quantum/crc.c

@@ -0,0 +1,59 @@
+/* Copyright 2021 QMK
+ *
+ * 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
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "crc.h"
+
+__attribute__((weak)) void crc_init(void){
+    /* Software implementation nothing todo here. */
+};
+
+#if defined(CRC8_USE_TABLE)
+/**
+ * Static table used for the table_driven implementation.
+ */
+static const crc_t crc_table[256] = {0x00, 0x07, 0x0e, 0x09, 0x1c, 0x1b, 0x12, 0x15, 0x38, 0x3f, 0x36, 0x31, 0x24, 0x23, 0x2a, 0x2d, 0x70, 0x77, 0x7e, 0x79, 0x6c, 0x6b, 0x62, 0x65, 0x48, 0x4f, 0x46, 0x41, 0x54, 0x53, 0x5a, 0x5d, 0xe0, 0xe7, 0xee, 0xe9, 0xfc, 0xfb, 0xf2, 0xf5, 0xd8, 0xdf, 0xd6, 0xd1, 0xc4, 0xc3, 0xca, 0xcd, 0x90, 0x97, 0x9e, 0x99, 0x8c, 0x8b, 0x82, 0x85, 0xa8, 0xaf, 0xa6, 0xa1, 0xb4, 0xb3, 0xba, 0xbd, 0xc7, 0xc0, 0xc9, 0xce, 0xdb, 0xdc, 0xd5, 0xd2, 0xff, 0xf8, 0xf1, 0xf6, 0xe3, 0xe4, 0xed, 0xea, 0xb7, 0xb0, 0xb9, 0xbe, 0xab, 0xac, 0xa5, 0xa2, 0x8f, 0x88, 0x81, 0x86, 0x93, 0x94, 0x9d, 0x9a, 0x27, 0x20, 0x29, 0x2e, 0x3b, 0x3c, 0x35, 0x32, 0x1f, 0x18, 0x11, 0x16, 0x03, 0x04, 0x0d, 0x0a, 0x57, 0x50, 0x59, 0x5e, 0x4b, 0x4c, 0x45, 0x42, 0x6f, 0x68, 0x61, 0x66, 0x73, 0x74, 0x7d, 0x7a,
+                                     0x89, 0x8e, 0x87, 0x80, 0x95, 0x92, 0x9b, 0x9c, 0xb1, 0xb6, 0xbf, 0xb8, 0xad, 0xaa, 0xa3, 0xa4, 0xf9, 0xfe, 0xf7, 0xf0, 0xe5, 0xe2, 0xeb, 0xec, 0xc1, 0xc6, 0xcf, 0xc8, 0xdd, 0xda, 0xd3, 0xd4, 0x69, 0x6e, 0x67, 0x60, 0x75, 0x72, 0x7b, 0x7c, 0x51, 0x56, 0x5f, 0x58, 0x4d, 0x4a, 0x43, 0x44, 0x19, 0x1e, 0x17, 0x10, 0x05, 0x02, 0x0b, 0x0c, 0x21, 0x26, 0x2f, 0x28, 0x3d, 0x3a, 0x33, 0x34, 0x4e, 0x49, 0x40, 0x47, 0x52, 0x55, 0x5c, 0x5b, 0x76, 0x71, 0x78, 0x7f, 0x6a, 0x6d, 0x64, 0x63, 0x3e, 0x39, 0x30, 0x37, 0x22, 0x25, 0x2c, 0x2b, 0x06, 0x01, 0x08, 0x0f, 0x1a, 0x1d, 0x14, 0x13, 0xae, 0xa9, 0xa0, 0xa7, 0xb2, 0xb5, 0xbc, 0xbb, 0x96, 0x91, 0x98, 0x9f, 0x8a, 0x8d, 0x84, 0x83, 0xde, 0xd9, 0xd0, 0xd7, 0xc2, 0xc5, 0xcc, 0xcb, 0xe6, 0xe1, 0xe8, 0xef, 0xfa, 0xfd, 0xf4, 0xf3};
+
+__attribute__((weak)) uint8_t crc8(const void *data, size_t data_len) {
+    const uint8_t *d   = (const uint8_t *)data;
+    crc_t          crc = 0xff;
+    size_t         tbl_idx;
+
+    while (data_len--) {
+        tbl_idx = crc ^ *d;
+        crc     = crc_table[tbl_idx] & 0xff;
+        d++;
+    }
+    return crc & 0xff;
+}
+#else
+__attribute__((weak)) uint8_t crc8(const void *data, size_t data_len) {
+    const uint8_t *d   = (const uint8_t *)data;
+    crc_t          crc = 0xff;
+    size_t         i, j;
+
+    for (i = 0; i < data_len; i++) {
+        crc ^= d[i];
+        for (j = 0; j < 8; j++) {
+            if ((crc & 0x80) != 0)
+                crc = (crc_t)((crc << 1) ^ 0x31);
+            else
+                crc <<= 1;
+        }
+    }
+    return crc;
+}
+#endif

quantum/crc.h

@@ -0,0 +1,44 @@
+/* Copyright 2021 QMK
+ *
+ * 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
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include "quantum.h"
+
+/**
+ * The type of the CRC values.
+ *
+ * This type must be big enough to contain at least 8 bits.
+ */
+#if defined(CRC8_OPTIMIZE_SPEED)
+typedef uint_fast8_t crc_t;
+#else
+typedef uint_least8_t crc_t;
+#endif
+
+/**
+ * Initialize crc subsystem.
+ */
+__attribute__((weak)) void crc_init(void);
+
+/**
+ * Generate CRC8 value from given data.
+ *
+ * \param[in] data     Pointer to a buffer of \a data_len bytes.
+ * \param[in] data_len Number of bytes in the \a data buffer.
+ * \return             The calculated crc value.
+ */
+__attribute__((weak)) uint8_t crc8(const void *data, size_t data_len);

tmk_core/common/keyboard.c

@@ -100,6 +100,9 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #ifdef EEPROM_DRIVER
 #    include "eeprom_driver.h"
 #endif
+#if defined(CRC_ENABLE)
+#    include "crc.h"
+#endif
 
 static uint32_t last_input_modification_time = 0;
 uint32_t        last_input_activity_time(void) { return last_input_modification_time; }
@@ -288,6 +291,9 @@ void keyboard_init(void) {
     timer_init();
     sync_timer_init();
     matrix_init();
+#if defined(CRC_ENABLE)
+    crc_init();
+#endif
 #ifdef VIA_ENABLE
     via_init();
 #endif