Hack out an initial i2c bus driver

display-i2c/main.c

@@ -1,5 +1,6 @@
 #include <display.h>
 #include <stdio.h>
+#include <i2c.h>
 
 int main(void) {
     display_t display = {

flake.nix

@@ -195,6 +195,21 @@
           ];
         };
 
+      packages."x86_64-linux"."i2c" =
+        { gcc, cflags }:
+        let
+          pkgs = import nixpkgs { system = "x86_64-linux"; };
+        in mkLibrary {
+          pkgs = pkgs;
+          gcc = gcc;
+          cflags = cflags;
+          pname = "i2c";
+          psrc = ./i2c;
+          pbuildInputs = [
+            (packages."x86_64-linux"."dio" { inherit gcc cflags; })
+          ];
+        };
+
       packages."x86_64-linux"."prime-tx" =
         { gcc, cflags }:
         let
@@ -304,9 +319,10 @@
 
           pbuildInputs = [
             (packages."x86_64-linux"."dio" { inherit gcc cflags; })
-            (packages."x86_64-linux"."spi" { inherit gcc cflags; })
-            (packages."x86_64-linux"."shift-register" { inherit gcc cflags; })
             (packages."x86_64-linux"."display" { inherit gcc cflags; })
+            (packages."x86_64-linux"."i2c" { inherit gcc cflags; })
+            (packages."x86_64-linux"."shift-register" { inherit gcc cflags; })
+            (packages."x86_64-linux"."spi" { inherit gcc cflags; })
           ];
         };
 

i2c/i2c.c

@@ -13,42 +13,185 @@ You should have received a copy of the GNU General Public License along with thi
 #include <util/delay.h>
 #include "i2c.h"
 
-void i2c_init_host(i2c_host_t *bus, i2c_error_e *error) {
-    dio_set_direction(&bus->sda, LINE_OUT);
-    dio_set(&bus->sda, 1);
-
-    dio_set_direction(&bus->scl, LINE_OUT);
-    dio_set(&bus->scl, 1);
+void i2c_delay(void) {
+    _delay_us(5);
 }
 
-void i2c_init_client(i2c_client_t *bus, i2c_error_e *error) {
+inline void set_sda(i2c_bus_t *bus) {
     dio_set_direction(&bus->sda, LINE_IN);
+}
+
+inline void clear_sda(i2c_bus_t *bus) {
+    dio_set(&bus->sda, 0);
+    dio_set_direction(&bus->sda, LINE_OUT);
+}
+
+inline uint8_t read_sda(i2c_bus_t *bus) {
+    return dio_read(&bus->sda);
+}
+
+inline void set_scl(i2c_bus_t *bus) {
     dio_set_direction(&bus->scl, LINE_IN);
 }
 
-void i2c_host_write_packet(i2c_host_t *bus, uint8_t value, i2c_error_e *error) {
-    dio_set(&bus->sda, 0);
+inline void clear_scl(i2c_bus_t *bus) {
     dio_set(&bus->scl, 0);
+    dio_set_direction(&bus->scl, LINE_OUT);
+}
+
+inline uint8_t read_scl(i2c_bus_t *bus) {
+    return dio_read(&bus->scl);
+}
+
+void i2c_init_host(i2c_bus_t *bus) {
+    set_sda(bus);
+    set_scl(bus);
+}
 
-    for (int i = 7; i >= 0; i--) {
-        dio_set(&bus->sda, value & _BV(i));
 /*
-        if (value & _BV(i)) {
-            dio_set(&bus->sda, 1);
-        } else {
-            dio_set(&bus->sda, 0);
+void i2c_init_client(i2c_client_t *bus) {
+    set_sda(bus);
+    set_scl(bus);
 }
 */
-        dio_set(&bus->scl, 1);
-        dio_set(&bus->scl, 0);
+
+void i2c_start_condition(i2c_bus_t *bus, i2c_error_e *error) {
+    if (*error != i2c_ok) return;
+
+    // TODO: handle the restart state
+
+    if (read_sda(bus) == 0) {
+        *error = i2c_arbitration_lost;
+        return;
     }
 
-    dio_set_direction(&bus->scl, LINE_IN);
-
+    clear_sda(bus);
+    i2c_delay();
+    clear_scl(bus);
 }
 
-void i2c_host_write(i2c_host_t *bus, uint8_t address, uint8_t *data, size_t length, i2c_error_e *error) {
-    if (*error) return;
+void i2c_end_condition(i2c_bus_t *bus, i2c_error_e *error) {
+    if (*error != i2c_ok) return;
+
+    clear_sda(bus);
+    i2c_delay();
+
+    set_scl(bus);
+
+    int count = 0;
+    while (read_scl(bus) == 0) {
+        if (count == 5) {
+            *error = i2c_timeout;
+            return;
+        }
+        count++;
+        i2c_delay();
+    }
+
+    i2c_delay();
+
+    set_sda(bus);
+    i2c_delay();
+
+    if (read_sda(bus) == 0) {
+        *error = i2c_arbitration_lost;
+    }
+}
+
+void i2c_write_bit(i2c_bus_t *bus, uint8_t value, i2c_error_e *error) {
+    if (*error != i2c_ok) return;
+
+    if (value) {
+        clear_sda(bus);
+    } else {
+        set_sda(bus);
+    }
+    i2c_delay();
+
+    set_scl(bus);
+    i2c_delay();
+
+    int count = 0;
+    while (read_scl(bus) == 0) {
+        if (count == 5) {
+            *error = i2c_timeout;
+            return;
+        }
+        count++;
+        i2c_delay();
+    }
+
+
+    if (value && (read_sda(bus) == 0)) {
+        *error = i2c_arbitration_lost;
+    }
+
+    clear_scl(bus);
+}
+
+uint8_t i2c_read_bit(i2c_bus_t *bus, i2c_error_e *error) {
+    uint8_t bit;
+
+    if (*error != i2c_ok) return 0;
+
+    set_sda(bus);
+    i2c_delay();
+
+    set_scl(bus);
+    int count = 0;
+    while (read_scl(bus) == 0) {
+        if (count == 5) {
+            *error = i2c_timeout;
+            return 0;
+        }
+        count++;
+        i2c_delay();
+    }
+    i2c_delay();
+
+    bit = read_sda(bus);
+    clear_scl(bus);
+    return bit;
+}
+
+void i2c_write_byte(i2c_bus_t *bus, uint8_t value, i2c_error_e *error) {
+    if (*error != i2c_ok) return;
+
+    for (int i = 7; i >= 0; i--) {
+        i2c_write_bit(bus, value & _BV(i), error);
+    }
+
+    uint8_t nak = i2c_read_bit(bus, error);
+    if (*error != i2c_ok) return;
+
+    if (nak) {
+        *error = i2c_nak;
+    }
+
+    return;
+}
+
+uint8_t i2c_read_byte(i2c_bus_t *bus, i2c_error_e *error) {
+    if (*error != i2c_ok) return 0;
+
+    uint8_t value = 0;
+    for (int i = 0; i < 8; i++) {
+        value = value << 1 | i2c_read_bit(bus, error);
+    }
+
+    if (*error != i2c_ok) {
+        i2c_error_e tmp_error;
+        i2c_write_bit(bus, 1, &tmp_error);
+        return 0;
+    }
+
+    i2c_write_bit(bus, 0, error);
+    return value;
+}
+
+/*
+void i2c_host_write(i2c_bus_t *bus, uint8_t address, uint8_t *data, size_t length, i2c_error_e *error) {
+    if (*error != i2c_ok) return;
 
     i2c_host_write_packet(bus, address << 1, error);
     if (*error != ok) return;
@@ -58,3 +201,4 @@ void i2c_host_write(i2c_host_t *bus, uint8_t address, uint8_t *data, size_t leng
         if (*error != ok) return;
     }
 }
+*/

i2c/i2c.h

@@ -13,27 +13,31 @@ You should have received a copy of the GNU General Public License along with thi
 #ifndef __I2C_H__
 #define __I2C_H__
 
-#include <base.h>
+#include <dio.h>
 
 typedef enum {
-    ok,
-    nak
+    i2c_ok,
+    i2c_arbitration_lost,
+    i2c_timeout,
+    i2c_nak,
 } i2c_error_e;
 
 typedef struct {
     dio_t sda;
-    dio_t clk;
-} i2c_host_t;
+    dio_t scl;
+} i2c_bus_t;
 
+/*
 typedef struct {
     dio_t sda;
-    dio_t clk;
+    dio_t scl;
     uint8_t addr;
-}
+} i2c_client_t;
+*/
 
-void i2c_init_host(i2c_host_t *, i2c_error_e *);
-void i2c_init_client(i2c_client_t *, i2c_error_e *); 
+void i2c_init_host(i2c_bus_t *);
+// void i2c_init_client(i2c_client_t *); 
 
-void i2c_host_write(i2c_host_t *, uint8_t, uint8_t, size_t, i2c_error_e);
+// void i2c_host_write(i2c_host_t *, uint8_t, uint8_t, size_t, i2c_error_e);
 
 #endif