examples/tcp_stm32f407.rs

@@ -17,7 +17,8 @@ use stm32f4xx_hal::{
     spi::Spi,
     time::Hertz
 };
-use enc424j600::smoltcp_phy;
+use enc424j600;
+use enc424j600::{smoltcp_phy, EthController};
 
 use smoltcp::wire::{
     EthernetAddress, IpAddress, IpCidr, Ipv6Cidr
@@ -77,7 +78,7 @@ use stm32f4xx_hal::{
         Alternate, AF5, Output, PushPull
     }
 };
-type SpiEth = enc424j600::Enc424j600<
+type BoosterSpiEth = enc424j600::SpiEth<
     Spi<SPI1, (PA5<Alternate<AF5>>, PA6<Alternate<AF5>>, PA7<Alternate<AF5>>)>,
     PA4<Output<PushPull>>,
     fn(u32) -> ()
@@ -101,7 +102,7 @@ const APP: () = {
     struct Resources {
         eth_iface: EthernetInterface<
             'static,
-            smoltcp_phy::SmoltcpDevice<SpiEth>>,
+            smoltcp_phy::SmoltcpDevice<BoosterSpiEth>>,
         itm: ITM
     }
 
@@ -156,11 +157,11 @@ const APP: () = {
                 let delay_ns_fp: fn(u32) -> () = |time_ns| {
                     cortex_m::asm::delay((time_ns*21)/125 + 1)
                 };
-                SpiEth::new(spi_eth_port, spi1_nss, delay_ns_fp)
+                enc424j600::SpiEth::new(spi_eth_port, spi1_nss, delay_ns_fp)
             };
 
             // Init controller
-            match spi_eth.reset() {
+            match spi_eth.init_dev() {
                 Ok(_) => {
                     iprintln!(stim0, "Initializing Ethernet...")
                 }
@@ -171,7 +172,7 @@ const APP: () = {
 
             // Read MAC
             let mut eth_mac_addr: [u8; 6] = [0; 6];
-            spi_eth.read_mac_addr(&mut eth_mac_addr);
+            spi_eth.read_from_mac(&mut eth_mac_addr);
             for i in 0..6 {
                 let byte = eth_mac_addr[i];
                 match i {

examples/tx_stm32f407.rs

@@ -17,7 +17,8 @@ use stm32f4xx_hal::{
     spi::Spi,
     time::Hertz
 };
-use enc424j600::EthPhy;
+use enc424j600;
+use enc424j600::EthController;
 
 ///
 use stm32f4xx_hal::{
@@ -27,16 +28,15 @@ use stm32f4xx_hal::{
         Alternate, AF5, Output, PushPull
     },
 };
-type SpiEth = enc424j600::Enc424j600<
+type BoosterSpiEth = enc424j600::SpiEth<
     Spi<SPI1, (PA5<Alternate<AF5>>, PA6<Alternate<AF5>>, PA7<Alternate<AF5>>)>,
     PA4<Output<PushPull>>,
-    fn(u32) -> ()
+    fn(u32)>;
->;
 
 #[rtic::app(device = stm32f4xx_hal::stm32, peripherals = true, monotonic = rtic::cyccnt::CYCCNT)]
 const APP: () = {
     struct Resources {
-        spi_eth: SpiEth,
+        spi_eth: BoosterSpiEth,
         delay: Delay,
         itm: ITM,
     }
@@ -87,11 +87,11 @@ const APP: () = {
             let delay_ns: fn(u32) -> () = |time_ns| {
                 cortex_m::asm::delay((time_ns*21)/125 + 1)
             };
-            SpiEth::new(spi_eth_port, spi1_nss, delay_ns)
+            enc424j600::SpiEth::new(spi_eth_port, spi1_nss, delay_ns)
         };
 
         // Init
-        match spi_eth.reset() {
+        match spi_eth.init_dev() {
             Ok(_) => {
                 iprintln!(stim0, "Initializing Ethernet...")
             }
@@ -102,7 +102,7 @@ const APP: () = {
 
         // Read MAC
         let mut eth_mac_addr: [u8; 6] = [0; 6];
-        spi_eth.read_mac_addr(&mut eth_mac_addr);
+        spi_eth.read_from_mac(&mut eth_mac_addr);
         for i in 0..6 {
             let byte = eth_mac_addr[i];
             match i {
@@ -157,7 +157,7 @@ const APP: () = {
                     _ => ()
                 };
             }
-            c.resources.spi_eth.send_packet(&eth_tx_packet);
+            c.resources.spi_eth.send_raw_packet(&eth_tx_packet);
             iprintln!(stim0, "Packet sent");
             c.resources.delay.delay_ms(100_u32);
         }

src/lib.rs

@@ -20,31 +20,36 @@ pub mod nal;
 /// Max raw frame array size
 pub const RAW_FRAME_LENGTH_MAX: usize = 1518;
 
-/// Trait representing PHY layer of ENC424J600
+pub trait EthController {
-pub trait EthPhy {
+    fn init_dev(&mut self) -> Result<(), EthControllerError>;
-    fn recv_packet(&mut self, is_poll: bool) -> Result<rx::RxPacket, Error>;
+    fn init_rxbuf(&mut self) -> Result<(), EthControllerError>;
-    fn send_packet(&mut self, packet: &tx::TxPacket) -> Result<(), Error>;
+    fn init_txbuf(&mut self) -> Result<(), EthControllerError>;
+    fn receive_next(&mut self, is_poll: bool) -> Result<rx::RxPacket, EthControllerError>;
+    fn send_raw_packet(&mut self, packet: &tx::TxPacket) -> Result<(), EthControllerError>;
+    fn set_promiscuous(&mut self) -> Result<(), EthControllerError>;
+    fn read_from_mac(&mut self, mac: &mut [u8]) -> Result<(), EthControllerError>;
+    fn write_mac_address(&mut self, mac: &[u8]) -> Result<(), EthControllerError>;
 }
 
 /// TODO: Improve these error types
 #[derive(Debug)]
-pub enum Error {
+pub enum EthControllerError {
     SpiPortError,
-    RegisterError,
+    GeneralError,
     // TODO: Better name?
     NoRxPacketError
 }
 
-impl From<spi::Error> for Error {
+impl From<spi::SpiPortError> for EthControllerError {
-    fn from(_: spi::Error) -> Error {
+    fn from(_: spi::SpiPortError) -> EthControllerError {
-        Error::SpiPortError
+        EthControllerError::SpiPortError
     }
 }
 
-/// ENC424J600 controller in SPI mode
+/// Ethernet controller using SPI interface
-pub struct Enc424j600<SPI: Transfer<u8>,
+pub struct SpiEth<SPI: Transfer<u8>,
-                      NSS: OutputPin,
+                  NSS: OutputPin,
-                      F: FnMut(u32) -> ()> {
+                  F: FnMut(u32) -> ()> {
     spi_port: spi::SpiPort<SPI, NSS, F>,
     rx_buf: rx::RxBuffer,
     tx_buf: tx::TxBuffer
@@ -52,29 +57,26 @@ pub struct Enc424j600<SPI: Transfer<u8>,
 
 impl <SPI: Transfer<u8>,
       NSS: OutputPin,
-      F: FnMut(u32) -> ()> Enc424j600<SPI, NSS, F> {
+      F: FnMut(u32) -> ()> SpiEth<SPI, NSS, F> {
     pub fn new(spi: SPI, nss: NSS, delay_ns: F) -> Self {
-        Enc424j600 {
+        SpiEth {
             spi_port: spi::SpiPort::new(spi, nss, delay_ns),
             rx_buf: rx::RxBuffer::new(),
             tx_buf: tx::TxBuffer::new()
         }
     }
+}
 
-    pub fn init(&mut self) -> Result<(), Error> {
+impl <SPI: Transfer<u8>,
-        self.reset()?;
+      NSS: OutputPin,
-        self.init_rxbuf()?;
+      F: FnMut(u32) -> ()> EthController for SpiEth<SPI, NSS, F> {
-        self.init_txbuf()?;
+    fn init_dev(&mut self) -> Result<(), EthControllerError> {
-        Ok(())
-    }
-
-    pub fn reset(&mut self) -> Result<(), Error> {
         // Write 0x1234 to EUDAST
         self.spi_port.write_reg_16b(spi::addrs::EUDAST, 0x1234)?;
         // Verify that EUDAST is 0x1234
         let mut eudast = self.spi_port.read_reg_16b(spi::addrs::EUDAST)?;
         if eudast != 0x1234 {
-            return Err(Error::RegisterError)
+            return Err(EthControllerError::GeneralError)
         }
         // Poll CLKRDY (ESTAT<12>) to check if it is set
         loop {
@@ -88,13 +90,13 @@ impl <SPI: Transfer<u8>,
         // Verify that EUDAST is 0x0000
         eudast = self.spi_port.read_reg_16b(spi::addrs::EUDAST)?;
         if eudast != 0x0000 {
-            return Err(Error::RegisterError)
+            return Err(EthControllerError::GeneralError)
         }
         self.spi_port.delay_us(256);
         Ok(())
     }
 
-    pub fn init_rxbuf(&mut self) -> Result<(), Error> {
+    fn init_rxbuf(&mut self) -> Result<(), EthControllerError> {
         // Set ERXST pointer
         self.spi_port.write_reg_16b(spi::addrs::ERXST, self.rx_buf.get_wrap_addr())?;
         // Set ERXTAIL pointer
@@ -107,57 +109,22 @@ impl <SPI: Transfer<u8>,
         Ok(())
     }
 
-    pub fn init_txbuf(&mut self) -> Result<(), Error> {
+    fn init_txbuf(&mut self) -> Result<(), EthControllerError> {
         // Set EGPWRPT pointer
         self.spi_port.write_reg_16b(spi::addrs::EGPWRPT, 0x0000)?;
         Ok(())
     }
 
-    /// Set controller to Promiscuous Mode
-    pub fn set_promiscuous(&mut self) -> Result<(), Error> {
-        // From Section 10.12, ENC424J600 Data Sheet:
-        // "To accept all incoming frames regardless of content (Promiscuous mode),
-        // set the CRCEN, RUNTEN, UCEN, NOTMEEN and MCEN bits."
-        let erxfcon_lo = self.spi_port.read_reg_8b(spi::addrs::ERXFCON)?;
-        self.spi_port.write_reg_8b(spi::addrs::ERXFCON, 0b0101_1110 | (erxfcon_lo & 0b1010_0001))?;
-        Ok(())
-    }
-
-    /// Read MAC to [u8; 6]
-    pub fn read_mac_addr(&mut self, mac: &mut [u8]) -> Result<(), Error> {
-        mac[0] = self.spi_port.read_reg_8b(spi::addrs::MAADR1)?;
-        mac[1] = self.spi_port.read_reg_8b(spi::addrs::MAADR1 + 1)?;
-        mac[2] = self.spi_port.read_reg_8b(spi::addrs::MAADR2)?;
-        mac[3] = self.spi_port.read_reg_8b(spi::addrs::MAADR2 + 1)?;
-        mac[4] = self.spi_port.read_reg_8b(spi::addrs::MAADR3)?;
-        mac[5] = self.spi_port.read_reg_8b(spi::addrs::MAADR3 + 1)?;
-        Ok(())
-    }
-
-    pub fn write_mac_addr(&mut self, mac: &[u8]) -> Result<(), Error> {
-        self.spi_port.write_reg_8b(spi::addrs::MAADR1, mac[0])?;
-        self.spi_port.write_reg_8b(spi::addrs::MAADR1 + 1, mac[1])?;
-        self.spi_port.write_reg_8b(spi::addrs::MAADR2, mac[2])?;
-        self.spi_port.write_reg_8b(spi::addrs::MAADR2 + 1, mac[3])?;
-        self.spi_port.write_reg_8b(spi::addrs::MAADR3, mac[4])?;
-        self.spi_port.write_reg_8b(spi::addrs::MAADR3 + 1, mac[5])?;
-        Ok(())
-    }
-}
-
-impl <SPI: Transfer<u8>,
-      NSS: OutputPin,
-      F: FnMut(u32) -> ()> EthPhy for Enc424j600<SPI, NSS, F> {
     /// Receive the next packet and return it
     /// Set is_poll to true for returning until PKTIF is set;
     /// Set is_poll to false for returning Err when PKTIF is not set
-    fn recv_packet(&mut self, is_poll: bool) -> Result<rx::RxPacket, Error> {
+    fn receive_next(&mut self, is_poll: bool) -> Result<rx::RxPacket, EthControllerError> {
         // Poll PKTIF (EIR<4>) to check if it is set
         loop {
             let eir = self.spi_port.read_reg_16b(spi::addrs::EIR)?;
             if eir & 0x40 == 0x40 { break }
             if !is_poll {
-                return Err(Error::NoRxPacketError)
+                return Err(EthControllerError::NoRxPacketError)
             }
         }
         // Set ERXRDPT pointer to next_addr
@@ -193,7 +160,7 @@ impl <SPI: Transfer<u8>,
     }
 
     /// Send an established packet
-    fn send_packet(&mut self, packet: &tx::TxPacket) -> Result<(), Error> {
+    fn send_raw_packet(&mut self, packet: &tx::TxPacket) -> Result<(), EthControllerError> {
         // Set EGPWRPT pointer to next_addr
         self.spi_port.write_reg_16b(spi::addrs::EGPWRPT, self.tx_buf.get_next_addr())?;
         // Copy packet data to SRAM Buffer
@@ -220,4 +187,35 @@ impl <SPI: Transfer<u8>,
             tx::GPBUFEN_DEFAULT);
         Ok(())
     }
+
+    /// Set controller to Promiscuous Mode
+    fn set_promiscuous(&mut self) -> Result<(), EthControllerError> {
+        // From Section 10.12, ENC424J600 Data Sheet:
+        // "To accept all incoming frames regardless of content (Promiscuous mode),
+        // set the CRCEN, RUNTEN, UCEN, NOTMEEN and MCEN bits."
+        let erxfcon_lo = self.spi_port.read_reg_8b(spi::addrs::ERXFCON)?;
+        self.spi_port.write_reg_8b(spi::addrs::ERXFCON, 0b0101_1110 | (erxfcon_lo & 0b1010_0001))?;
+        Ok(())
+    }
+
+    /// Read MAC to [u8; 6]
+    fn read_from_mac(&mut self, mac: &mut [u8]) -> Result<(), EthControllerError> {
+        mac[0] = self.spi_port.read_reg_8b(spi::addrs::MAADR1)?;
+        mac[1] = self.spi_port.read_reg_8b(spi::addrs::MAADR1 + 1)?;
+        mac[2] = self.spi_port.read_reg_8b(spi::addrs::MAADR2)?;
+        mac[3] = self.spi_port.read_reg_8b(spi::addrs::MAADR2 + 1)?;
+        mac[4] = self.spi_port.read_reg_8b(spi::addrs::MAADR3)?;
+        mac[5] = self.spi_port.read_reg_8b(spi::addrs::MAADR3 + 1)?;
+        Ok(())
+    }
+
+    fn write_mac_address(&mut self, mac: &[u8]) -> Result<(), EthControllerError> {
+        self.spi_port.write_reg_8b(spi::addrs::MAADR1, mac[0])?;
+        self.spi_port.write_reg_8b(spi::addrs::MAADR1 + 1, mac[1])?;
+        self.spi_port.write_reg_8b(spi::addrs::MAADR2, mac[2])?;
+        self.spi_port.write_reg_8b(spi::addrs::MAADR2 + 1, mac[3])?;
+        self.spi_port.write_reg_8b(spi::addrs::MAADR3, mac[4])?;
+        self.spi_port.write_reg_8b(spi::addrs::MAADR3 + 1, mac[5])?;
+        Ok(())
+    }
 }

src/nal.rs

@@ -24,7 +24,7 @@ pub enum NetworkError {
 pub type NetworkInterface<SPI, NSS> = net::iface::EthernetInterface<
     'static,
     crate::smoltcp_phy::SmoltcpDevice<
-        crate::Enc424j600<SPI, NSS, fn(u32)>
+        crate::SpiEth<SPI, NSS, fn(u32)>
     >,
 >;
 

src/smoltcp_phy.rs

@@ -1,5 +1,5 @@
 use crate::{
-    EthPhy, tx, RAW_FRAME_LENGTH_MAX
+    EthController, tx, RAW_FRAME_LENGTH_MAX
 };
 use core::cell;
 use smoltcp::{
@@ -8,25 +8,25 @@ use smoltcp::{
     Error
 };
 
-pub struct SmoltcpDevice<E: EthPhy> {
+pub struct SmoltcpDevice<EC: EthController> {
-    pub eth_phy: cell::RefCell<E>,
+    pub eth_controller: cell::RefCell<EC>,
     rx_packet_buf: [u8; RAW_FRAME_LENGTH_MAX],
     tx_packet_buf: [u8; RAW_FRAME_LENGTH_MAX]
 }
 
-impl<E: EthPhy> SmoltcpDevice<E> {
+impl<EC: EthController> SmoltcpDevice<EC> {
-    pub fn new(eth_phy: E) -> Self {
+    pub fn new(eth_controller: EC) -> Self {
         SmoltcpDevice {
-            eth_phy: cell::RefCell::new(eth_phy),
+            eth_controller: cell::RefCell::new(eth_controller),
             rx_packet_buf: [0; RAW_FRAME_LENGTH_MAX],
             tx_packet_buf: [0; RAW_FRAME_LENGTH_MAX]
         }
     }
 }
 
-impl<'a, E: 'a + EthPhy> Device<'a> for SmoltcpDevice<E> {
+impl<'a, EC: 'a + EthController> Device<'a> for SmoltcpDevice<EC> {
     type RxToken = EthRxToken<'a>;
-    type TxToken = EthTxToken<'a, E>;
+    type TxToken = EthTxToken<'a, EC>;
 
     fn capabilities(&self) -> DeviceCapabilities {
         let mut caps = DeviceCapabilities::default();
@@ -35,8 +35,8 @@ impl<'a, E: 'a + EthPhy> Device<'a> for SmoltcpDevice<E> {
     }
 
     fn receive(&'a mut self) -> Option<(Self::RxToken, Self::TxToken)> {
-        let self_p = (&mut *self) as *mut SmoltcpDevice<E>;
+        let self_p = (&mut *self) as *mut SmoltcpDevice<EC>;
-        match self.eth_phy.borrow_mut().recv_packet(false) {
+        match self.eth_controller.borrow_mut().receive_next(false) {
             Ok(rx_packet) => {
                 // Write received packet to RX packet buffer
                 rx_packet.write_frame_to(&mut self.rx_packet_buf);
@@ -57,7 +57,7 @@ impl<'a, E: 'a + EthPhy> Device<'a> for SmoltcpDevice<E> {
     }
 
     fn transmit(&'a mut self) -> Option<Self::TxToken> {
-        let self_p = (&mut *self) as *mut SmoltcpDevice<E>;
+        let self_p = (&mut *self) as *mut SmoltcpDevice<EC>;
         // Construct a blank TxToken
         let tx_token = EthTxToken {
             buf: &mut self.tx_packet_buf,
@@ -81,12 +81,12 @@ impl<'a> RxToken for EthRxToken<'a> {
     }
 }
 
-pub struct EthTxToken<'a, E: EthPhy> {
+pub struct EthTxToken<'a, EC: EthController> {
     buf: &'a mut [u8],
-    dev: *mut SmoltcpDevice<E>
+    dev: *mut SmoltcpDevice<EC>
 }
 
-impl<'a, E: 'a + EthPhy> TxToken for EthTxToken<'a, E> {
+impl<'a, EC: 'a + EthController> TxToken for EthTxToken<'a, EC> {
     fn consume<R, F>(self, _timestamp: Instant, len: usize, f: F) -> Result<R, Error>
     where
         F: FnOnce(&mut [u8]) -> Result<R, Error>,
@@ -97,10 +97,10 @@ impl<'a, E: 'a + EthPhy> TxToken for EthTxToken<'a, E> {
         // Update frame length and write frame bytes
         tx_packet.update_frame(&mut self.buf[..len], len);
         // Send the packet as raw
-        let eth_phy = unsafe {
+        let eth_controller = unsafe {
-            &mut (*self.dev).eth_phy
+            &mut (*self.dev).eth_controller
         };
-        match eth_phy.borrow_mut().send_packet(&tx_packet) {
+        match eth_controller.borrow_mut().send_raw_packet(&tx_packet) {
             Ok(_) => { result },
             Err(_) => Err(Error::Exhausted)
         }

src/spi.rs

@@ -59,7 +59,7 @@ pub struct SpiPort<SPI: Transfer<u8>,
     delay_ns: F,
 }
 
-pub enum Error {
+pub enum SpiPortError {
     TransferError
 }
 
@@ -78,13 +78,13 @@ impl <SPI: Transfer<u8>,
         }
     }
 
-    pub fn read_reg_8b(&mut self, addr: u8) -> Result<u8, Error> {
+    pub fn read_reg_8b(&mut self, addr: u8) -> Result<u8, SpiPortError> {
         // Using RCRU instruction to read using unbanked (full) address
         let r_data = self.rw_addr_u8(opcodes::RCRU, addr, 0)?;
         Ok(r_data)
     }
 
-    pub fn read_reg_16b(&mut self, lo_addr: u8) -> Result<u16, Error> {
+    pub fn read_reg_16b(&mut self, lo_addr: u8) -> Result<u16, SpiPortError> {
         let r_data_lo = self.read_reg_8b(lo_addr)?;
         let r_data_hi = self.read_reg_8b(lo_addr + 1)?;
         // Combine top and bottom 8-bit to return 16-bit
@@ -93,7 +93,7 @@ impl <SPI: Transfer<u8>,
 
     // Currently requires manual slicing (buf[1..]) for the data read back
     pub fn read_rxdat<'a>(&mut self, buf: &'a mut [u8], data_length: usize)
-                         -> Result<(), Error> {
+                         -> Result<(), SpiPortError> {
         let r_valid = self.r_n(buf, opcodes::RERXDATA, data_length)?;
         Ok(r_valid)
     }
@@ -101,19 +101,19 @@ impl <SPI: Transfer<u8>,
     // Currenly requires actual data to be stored in buf[1..] instead of buf[0..]
     // TODO: Maybe better naming?
     pub fn write_txdat<'a>(&mut self, buf: &'a mut [u8], data_length: usize)
-                          -> Result<(), Error> {
+                          -> Result<(), SpiPortError> {
         let w_valid = self.w_n(buf, opcodes::WEGPDATA, data_length)?;
         Ok(w_valid)
     }
 
-    pub fn write_reg_8b(&mut self, addr: u8, data: u8) -> Result<(), Error> {
+    pub fn write_reg_8b(&mut self, addr: u8, data: u8) -> Result<(), SpiPortError> {
         // TODO: addr should be separated from w_data
         // Using WCRU instruction to write using unbanked (full) address
         self.rw_addr_u8(opcodes::WCRU, addr, data)?;
         Ok(())
     }
 
-    pub fn write_reg_16b(&mut self, lo_addr: u8, data: u16) -> Result<(), Error> {
+    pub fn write_reg_16b(&mut self, lo_addr: u8, data: u16) -> Result<(), SpiPortError> {
         self.write_reg_8b(lo_addr, (data & 0xff) as u8)?;
         self.write_reg_8b(lo_addr + 1, ((data & 0xff00) >> 8) as u8)?;
         Ok(())
@@ -127,7 +127,7 @@ impl <SPI: Transfer<u8>,
     // TODO: (Make data read/write as reference to array)
     // Currently requires 1-byte addr, read/write data is only 1-byte
     fn rw_addr_u8(&mut self, opcode: u8, addr: u8, data: u8)
-                 -> Result<u8, Error> {
+                 -> Result<u8, SpiPortError> {
         // Enable chip select
         self.nss.set_low();
         // Start writing to SLAVE
@@ -150,7 +150,7 @@ impl <SPI: Transfer<u8>,
                 (self.delay_ns)(60);
                 self.nss.set_high();
                 (self.delay_ns)(30);
-                Err(Error::TransferError)
+                Err(SpiPortError::TransferError)
             }
         }
     }
@@ -161,7 +161,7 @@ impl <SPI: Transfer<u8>,
     // Note: buf must be at least (data_length + 1)-byte long
     // TODO: Check and raise error for array size < (data_length + 1)
     fn r_n<'a>(&mut self, buf: &'a mut [u8], opcode: u8, data_length: usize)
-              -> Result<(), Error> {
+              -> Result<(), SpiPortError> {
         // Enable chip select
         self.nss.set_low();
         // Start writing to SLAVE
@@ -176,7 +176,7 @@ impl <SPI: Transfer<u8>,
             Err(_) => {
                 // Disable chip select
                 self.nss.set_high();
-                Err(Error::TransferError)
+                Err(SpiPortError::TransferError)
             }
         }
     }
@@ -184,7 +184,7 @@ impl <SPI: Transfer<u8>,
     // Note: buf[0] is currently reserved for opcode to overwrite
     // TODO: Actual data should start from buf[0], not buf[1]
     fn w_n<'a>(&mut self, buf: &'a mut [u8], opcode: u8, data_length: usize)
-              -> Result<(), Error> {
+              -> Result<(), SpiPortError> {
         // Enable chip select
         self.nss.set_low();
         // Start writing to SLAVE
@@ -200,8 +200,8 @@ impl <SPI: Transfer<u8>,
             Err(_) => {
                 // Disable chip select
                 self.nss.set_high();
-                Err(Error::TransferError)
+                Err(SpiPortError::TransferError)
             }
         }
     }
-}
+}