Kernel Module for the SPCD Device, which exposes control point interfaces, but does not include control algorithms.
The driver implements a character buffer interface at /dev/spcd0 that supports select() polling for interrupt based inputs and a device command set.
Reads occur one byte at a time. Each byte is a packed bitmask. The high bit, (bit 7) is set at power-on as a one-shot read of the dealer_enable during driver initialization. If it's high, then the software should start into 'dealer' mode.
X preboot_stat
| | 12v
| | | failsafe
| | | | valve_open
| | | | | overpressure
| | | | | | stuck_on
| | | | | | | dealer_enable
| | | | | | | |
Bit: 7 6 5 4 3 2 1 0
Writes to the character device are commands. Each command has an expected structure:
One byte command followed by two u64 values representing nanoseconds of period and duty of the PWM.
| 0x01 | u64 (period) | u64 (duty cycle) |
One byte command followed by a list of valve PWM states to iterate in a loop. Each valve state has a period, duty-cycle, and duration to hold the state before progressing to the next state.
Command:
| 0x02 | u8 (number of cycles) | cycle_definition |
cycle_definition:
| u64 (period) | u64 (duty cycle) | u64 (duration) |
Example: Alternate the valve between two duty cycles every 5000000 ns: You'd write a u8, followed by
u8 Command
| u8 Cycle Count
| | (6) u64 defining the two cycles.
| | |
| 0x02 | 0x02 | 0x0000000001312D00 | 0x0000000002625A00 | 0x00000000004C4B40 | 0x000000000065B9AA | 0x0000000002625A00 | 0x00000000004C4B40 |
Single-byte command, 0x04.
Single-byte command, 0x08.
The sysfs interface populates a virtual filesystem under sysfs. Change the working directory to:
cd /sys/bus/platform/devices/spcd@0 (which is a link to /sys/devices/soc0/spcd@0) to see options you have for interacting with the spcd.
The following files are read-only inputs which will contain 0 or 1:
status_12v
stuck_on
valve_open
overpressure
mode_switch
preboot_stat
Example: To read the immediate value of mode_switch.
cat /sys/bus/platform/devices/spcd@0/mode_switch
The following files are read/write and will respond to 0 or 1 being written to the file:
pwr_hold
postboot_stat
one_min
The following outputs control the hardware PWM timers for the blower and valve.
blower_period
blower_duty_cycle
valve_period
valve_duty_cycle
These files are read/write, and specify the timing in nanoseconds for the PWM Square wave.
Example: Set blower 50% duty_cycle cycle at 100Hz
echo "10000000" > /sys/bus/platform/devices/spcd@0/blower_period
echo "5000000" > /sys/bus/platform/devices/spcd@0/blower_duty_cycle
Example: Read current settings of blower:
$ cat /sys/bus/platform/devices/spcd@0/blower_period
8675309
$ cat /sys/bus/platform/devices/spcd@0/blower_duty_cycle
1337
To disable PWM, set the duty cycles to zero.