linux: implement i2c

Signed-off-by:  Eric Callahan <arksine.code@gmail.com>

1 files changed, 101 insertions, 0 deletions

diff --git a/src/linux/i2c.c b/src/linux/i2c.c
new file mode 100644
index 00000000..b8e8f253
--- /dev/null
+++ b/src/linux/i2c.c
@@ -0,0 +1,101 @@
+// Linux i2c implementation
+//
+// Copyright (C) 2020  Eric Callahan <arksine.code@gmail.com>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+#include <fcntl.h> // open
+#include <linux/i2c-dev.h> // I2C_SLAVE
+#include <stdio.h> // snprintf
+#include <sys/ioctl.h> // ioctl
+#include <unistd.h> // write
+#include "gpio.h" // i2c_setup
+#include "command.h" // shutdown
+#include "internal.h" // report_errno
+#include "sched.h" // sched_shutdown
+
+DECL_ENUMERATION_RANGE("i2c_bus", "i2c.0", 0, 2);
+
+struct i2c_s {
+    uint32_t bus;
+    uint8_t addr;
+    int fd;
+};
+
+static struct i2c_s devices[16];
+static int devices_count;
+
+static int
+i2c_open(uint32_t bus, uint8_t addr)
+{
+    // Find existing device (if already opened)
+    int i;
+    for (i=0; i<devices_count; i++) {
+        if (devices[i].bus == bus && devices[i].addr == addr) {
+            return devices[i].fd;
+        }
+    }
+
+    char fname[256];
+    snprintf(fname, sizeof(fname), "/dev/i2c-%d", bus);
+    int fd = open(fname, O_RDWR|O_CLOEXEC);
+    if (fd < 0) {
+        report_errno("open i2c", fd);
+        goto fail;
+    }
+    int ret = ioctl(fd, I2C_SLAVE, addr);
+    if (ret < 0) {
+        report_errno("ioctl i2c", fd);
+        goto fail;
+    }
+    ret = set_non_blocking(fd);
+    if (ret < 0)
+        goto fail;
+
+    devices[devices_count].bus = bus;
+    devices[devices_count].addr = addr;
+    devices[devices_count].fd = fd;
+    devices_count++;
+
+    return fd;
+
+fail:
+    if (fd >= 0)
+        close(fd);
+    shutdown("Unable to open i2c device");
+}
+
+struct i2c_config
+i2c_setup(uint32_t bus, uint32_t rate, uint8_t addr)
+{
+    // Note:  The rate is set by the kernel driver, for a Raspberry Pi this
+    // is done with the following setting in /boot/config.txt:
+    //
+    // dtparam=i2c_baudrate=<rate>
+
+    int fd = i2c_open(bus, addr);
+    return (struct i2c_config){.fd=fd};
+}
+
+void
+i2c_write(struct i2c_config config, uint8_t write_len, uint8_t *data)
+{
+    int ret = write(config.fd, data, write_len);
+    if (ret != write_len) {
+        if (ret < 0)
+            report_errno("write value i2c", ret);
+        try_shutdown("Unable write i2c device");
+    }
+}
+
+void
+i2c_read(struct i2c_config config, uint8_t reg_len, uint8_t *reg
+         , uint8_t read_len, uint8_t *data)
+{
+    i2c_write(config, reg_len, reg);
+    int ret = read(config.fd, data, read_len);
+    if (ret != read_len) {
+        if (ret < 0)
+            report_errno("read value i2c", ret);
+        try_shutdown("Unable to read i2c device");
+    }
+}