On Thu, 28 Mar 2019 14:53:28 -0700, Dave Stevens said:
> In the article below about kernel updates is a reference to a driver for
> a Plantower PMS7003 particulate matter sensor. I'm using this series in
> air pollution monitoring and its usual interface to the computer
> is over a serial line. I consequently am very curious about how and why
> it would need a specific kernel module.
A quick look at the driver shows that it apparently does at least
a little bit of the heavy lifting for you - rather than you have to do all the
serial I/O interpretation yourself in userspace, it will handle checksums and
channels and so on for you.
+enum pms7003_cmd {
+ CMD_WAKEUP,
+ CMD_ENTER_PASSIVE_MODE,
+ CMD_READ_PASSIVE,
+ CMD_SLEEP,
+};
+
+/*
+ * commands have following format:
+ *
+ * +------+------+-----+------+-----+-----------+-----------+
+ * | 0x42 | 0x4d | cmd | 0x00 | arg | cksum msb | cksum lsb |
+ * +------+------+-----+------+-----+-----------+-----------+
+ */
+static const u8 pms7003_cmd_tbl[][PMS7003_CMD_LENGTH] = {
+ [CMD_WAKEUP] = { 0x42, 0x4d, 0xe4, 0x00, 0x01, 0x01, 0x74 },
+ [CMD_ENTER_PASSIVE_MODE] = { 0x42, 0x4d, 0xe1, 0x00, 0x00, 0x01, 0x70 },
+ [CMD_READ_PASSIVE] = { 0x42, 0x4d, 0xe2, 0x00, 0x00, 0x01, 0x71 },
+ [CMD_SLEEP] = { 0x42, 0x4d, 0xe4, 0x00, 0x00, 0x01, 0x73 },
+};
So you can send 'wakeup' or 'read' and it will send the strings, and
then read back data and complete the I/O when enough bytes have
arrived.
There's also some probing in there to deal with device tree etc.
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