expose pca954x_select api (#167)

PR accompanying to ARTIQ's PCA954X support (#1860).
Co-authored-by: mwojcik <mw@m-labs.hk>
Co-committed-by: mwojcik <mw@m-labs.hk>

src/libboard_artiq/src/drtioaux_proto.rs

@@ -47,6 +47,7 @@ pub enum Packet {
     I2cReadRequest { destination: u8, busno: u8, ack: bool },
     I2cReadReply { succeeded: bool, data: u8 },
     I2cBasicReply { succeeded: bool },
+    I2cSwitchSelectRequest { destination: u8, busno: u8, address: u8, mask: u8 },
 
     SpiSetConfigRequest { destination: u8, busno: u8, flags: u8, length: u8, div: u8, cs: u8 },
     SpiWriteRequest { destination: u8, busno: u8, data: u32 },
@@ -152,6 +153,12 @@ impl Packet {
             0x87 => Packet::I2cBasicReply {
                 succeeded: reader.read_bool()?
             },
+            0x88 => Packet::I2cSwitchSelectRequest {
+                destination: reader.read_u8()?,
+                busno: reader.read_u8()?,
+                address: reader.read_u8()?,
+                mask: reader.read_u8()?
+            },
 
             0x90 => Packet::SpiSetConfigRequest {
                 destination: reader.read_u8()?,
@@ -301,6 +308,13 @@ impl Packet {
                 writer.write_u8(0x87)?;
                 writer.write_bool(succeeded)?;
             },
+            Packet::I2cSwitchSelectRequest { destination, busno, address, mask } => {
+                writer.write_u8(0x88)?;
+                writer.write_u8(destination)?;
+                writer.write_u8(busno)?;
+                writer.write_u8(address)?;
+                writer.write_u8(mask)?;
+            },
 
             Packet::SpiSetConfigRequest { destination, busno, flags, length, div, cs } => {
                 writer.write_u8(0x90)?;

src/runtime/src/i2c.rs

@@ -60,6 +60,29 @@ pub extern fn read(busno: i32, ack: bool) -> i32 {
     }
 }
 
+pub extern fn switch_select(busno: i32, address: i32, mask: i32) {
+    if busno > 0 {
+        artiq_raise!("I2CError", "I2C bus could not be accessed");
+    }
+    let ch = match mask { //decode from mainline, PCA9548-centric API
+        0x00 => None,
+        0x01 => Some(0),
+        0x02 => Some(1),
+        0x04 => Some(2),
+        0x08 => Some(3),
+        0x10 => Some(4),
+        0x20 => Some(5),
+        0x40 => Some(6),
+        0x80 => Some(7),
+        _ => artiq_raise!("I2CError", "switch select supports only one channel")
+    };
+    unsafe {
+        if (&mut I2C_BUS).as_mut().unwrap().pca954x_select(address as u8, ch).is_err() {
+            artiq_raise!("I2CError", "switch select failed");
+        }
+    }
+}
+
 pub fn init() {
     let mut i2c = libboard_zynq::i2c::I2c::i2c0();
     i2c.init().expect("I2C bus initialization failed");

src/runtime/src/kernel/api.rs

@@ -116,6 +116,7 @@ pub fn resolve(required: &[u8]) -> Option<u32> {
         api!(i2c_stop = i2c::stop),
         api!(i2c_write = i2c::write),
         api!(i2c_read = i2c::read),
+        api!(i2c_switch_select = i2c::switch_select),
 
         // Double-precision floating-point arithmetic helper functions
         // RTABI chapter 4.1.2, Table 2

src/satman/src/main.rs

@@ -282,6 +282,23 @@ fn process_aux_packet(_repeaters: &mut [repeater::Repeater],
                     &drtioaux::Packet::I2cReadReply { succeeded: false, data: 0xff })
             }
         }
+        drtioaux::Packet::I2cSwitchSelectRequest { destination: _destination, busno: _busno, address, mask } => {
+            forward!(_routing_table, _destination, *_rank, _repeaters, &packet, timer);
+            ch = match mask { //decode from mainline, PCA9548-centric API
+                0x00 => None,
+                0x01 => Some(0),
+                0x02 => Some(1),
+                0x04 => Some(2),
+                0x08 => Some(3),
+                0x10 => Some(4),
+                0x20 => Some(5),
+                0x40 => Some(6),
+                0x80 => Some(7),
+                _ => { return drtioaux::send(0, &drtioaux::Packet::I2cBasicReply { succeeded: false }); }
+            };
+            let succeeded = i2c.pca954x_select(address, ch).is_ok();
+            drtioaux::send(0, &drtioaux::Packet::I2cBasicReply { succeeded: succeeded })
+        }
 
         drtioaux::Packet::SpiSetConfigRequest { destination: _destination, busno: _busno, 
                                                 flags: _flags, length: _length, div: _div, cs: _cs } => {