manual: add short description of drivers, with replace support information. Closes #777

artiq/coredevice/ad5360.py

@@ -1,3 +1,11 @@
+"""
+Driver for the AD5360 DAC on RTIO.
+
+Output event replacement is not supported and issuing commands at the same
+time is an error.
+"""
+
+
 from artiq.language.core import (kernel, portable, delay_mu, delay)
 from artiq.language.units import ns, us
 from artiq.coredevice import spi

artiq/coredevice/dds.py

@@ -1,3 +1,11 @@
+"""
+Drivers for direct digital synthesis (DDS) chips on RTIO.
+
+Output event replacement is not supported and issuing commands at the same
+time is an error.
+"""
+
+
 from artiq.language.core import *
 from artiq.language.types import *
 from artiq.language.units import *

artiq/coredevice/i2c.py

@@ -1,3 +1,8 @@
+"""
+Non-realtime drivers for I2C chips on the core device.
+"""
+
+
 from artiq.language.core import syscall, kernel
 from artiq.language.types import TBool, TInt32, TNone
 from artiq.coredevice.exceptions import I2CError

artiq/coredevice/sawg.py

@@ -1,3 +1,13 @@
+"""
+Driver for the Smart Arbitrary Waveform Generator (SAWG) on RTIO.
+
+The SAWG is an "improved DDS" built in gateware and interfacing to
+high-speed DACs.
+
+Output event replacement is supported except on the configuration channel.
+"""
+
+
 from artiq.language.types import TInt32, TFloat
 from numpy import int32, int64
 from artiq.language.core import kernel, now_mu

artiq/coredevice/spi.py

@@ -1,3 +1,11 @@
+"""
+Driver for generic SPI on RTIO.
+
+Output event replacement is not supported and issuing commands at the same
+time is an error.
+"""
+
+
 import numpy
 
 from artiq.language.core import syscall, kernel, portable, now_mu, delay_mu

artiq/coredevice/ttl.py

@@ -1,3 +1,11 @@
+"""
+Drivers for TTL signals on RTIO.
+
+TTL channels (including the clock generator) all support output event
+replacement. For example, pulses of "zero" length (e.g. ``on()``
+immediately followed by ``off()``, without a delay) are suppressed.
+"""
+
 import numpy
 
 from artiq.language.core import *