87 lines
3.7 KiB
Rust
87 lines
3.7 KiB
Rust
use super::{Channel, Error};
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/// Provide an interface for managing digital attenuators on Pounder hardware.
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///
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/// Note: The digital attenuators do not allow read-back of attenuation. To circumvent this, this
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/// driver maintains the attenuation code in both the shift register as well as the latched output
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/// register of the attenuators. This allows the "active" attenuation code to be read back by
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/// reading the shfit register. The downside of this approach is that any read is destructive, so a
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/// read-writeback approach is employed.
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pub trait AttenuatorInterface {
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/// Set the attenuation of a single channel.
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///
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/// Args:
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/// * `channel` - The pounder channel to configure the attenuation of.
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/// * `attenuation` - The desired attenuation of the channel in dB. This has a resolution of
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/// 0.5dB.
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fn set_attenuation(
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&mut self,
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channel: Channel,
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attenuation: f32,
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) -> Result<f32, Error> {
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if !(0.0..=31.5).contains(&attenuation) {
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return Err(Error::Bounds);
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}
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// Calculate the attenuation code to program into the attenuator. The attenuator uses a
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// code where the LSB is 0.5 dB.
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let attenuation_code = (attenuation * 2.0) as u8;
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// Read all the channels, modify the channel of interest, and write all the channels back.
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// This ensures the staging register and the output register are always in sync.
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let mut channels = [0_u8; 4];
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self.read_all_attenuators(&mut channels)?;
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// The lowest 2 bits of the 8-bit shift register on the attenuator are ignored. Shift the
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// attenuator code into the upper 6 bits of the register value. Note that the attenuator
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// treats inputs as active-low, so the code is inverted before writing.
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channels[channel as usize] = (!attenuation_code) << 2;
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self.write_all_attenuators(&channels)?;
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// Finally, latch the output of the updated channel to force it into an active state.
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self.latch_attenuators(channel)?;
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Ok(attenuation_code as f32 / 2.0)
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}
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/// Get the attenuation of a channel.
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///
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/// Args:
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/// * `channel` - The channel to get the attenuation of.
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///
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/// Returns:
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/// The programmed attenuation of the channel in dB.
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fn get_attenuation(&mut self, channel: Channel) -> Result<f32, Error> {
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let mut channels = [0_u8; 4];
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// Reading the data always shifts data out of the staging registers, so we perform a
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// duplicate write-back to ensure the staging register is always equal to the output
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// register.
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self.read_all_attenuators(&mut channels)?;
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self.write_all_attenuators(&channels)?;
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// The attenuation code is stored in the upper 6 bits of the register, where each LSB
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// represents 0.5 dB. The attenuator stores the code as active-low, so inverting the result
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// (before the shift) has the affect of transforming the bits of interest (and the
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// dont-care bits) into an active-high state and then masking off the don't care bits. If
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// the shift occurs before the inversion, the upper 2 bits (which would then be don't
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// care) would contain erroneous data.
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let attenuation_code = (!channels[channel as usize]) >> 2;
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// Convert the desired channel code into dB of attenuation.
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Ok(attenuation_code as f32 / 2.0)
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}
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fn reset_attenuators(&mut self) -> Result<(), Error>;
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fn latch_attenuators(&mut self, channel: Channel) -> Result<(), Error>;
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fn read_all_attenuators(
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&mut self,
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channels: &mut [u8; 4],
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) -> Result<(), Error>;
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fn write_all_attenuators(
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&mut self,
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channels: &[u8; 4],
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) -> Result<(), Error>;
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}
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