diff --git a/examples/tcp_stm32f407.rs b/examples/tcp_stm32f407.rs
index b841517..80e3278 100644
--- a/examples/tcp_stm32f407.rs
+++ b/examples/tcp_stm32f407.rs
@@ -80,7 +80,9 @@ use stm32f4xx_hal::{
 };
 type BoosterSpiEth = enc424j600::SpiEth<
     Spi<SPI1, (PA5<Alternate<AF5>>, PA6<Alternate<AF5>>, PA7<Alternate<AF5>>)>,
-    PA4<Output<PushPull>>>;
+    PA4<Output<PushPull>>,
+    fn(u32) -> ()
+>;
 
 pub struct NetStorage {
     ip_addrs: [IpCidr; 1],
@@ -153,11 +155,15 @@ const APP: () = {
                     enc424j600::spi::interfaces::SPI_MODE,
                     Hertz(enc424j600::spi::interfaces::SPI_CLOCK_FREQ),
                     clocks);
-                enc424j600::SpiEth::new(spi_eth_port, spi1_nss)
+
+                let delay_ns_fp: fn(u32) -> () = |time_ns| {
+                    cortex_m::asm::delay((time_ns*21)/125 + 1)
+                };
+                enc424j600::SpiEth::new(spi_eth_port, spi1_nss, delay_ns_fp)
             };
 
             // Init controller
-            match spi_eth.init_dev(&mut delay) {
+            match spi_eth.init_dev() {
                 Ok(_) => {
                     iprintln!(stim0, "Initializing Ethernet...")
                 }
diff --git a/examples/tx_stm32f407.rs b/examples/tx_stm32f407.rs
index 4dd10ac..268e254 100644
--- a/examples/tx_stm32f407.rs
+++ b/examples/tx_stm32f407.rs
@@ -30,7 +30,8 @@ use stm32f4xx_hal::{
 };
 type BoosterSpiEth = enc424j600::SpiEth<
     Spi<SPI1, (PA5<Alternate<AF5>>, PA6<Alternate<AF5>>, PA7<Alternate<AF5>>)>,
-    PA4<Output<PushPull>>>;
+    PA4<Output<PushPull>>,
+    fn(u32)>;
 
 #[rtic::app(device = stm32f4xx_hal::stm32, peripherals = true, monotonic = rtic::cyccnt::CYCCNT)]
 const APP: () = {
@@ -82,11 +83,15 @@ const APP: () = {
                 enc424j600::spi::interfaces::SPI_MODE,
                 Hertz(enc424j600::spi::interfaces::SPI_CLOCK_FREQ),
                 clocks);
-            enc424j600::SpiEth::new(spi_eth_port, spi1_nss)
+
+            let delay_ns: fn(u32) -> () = |time_ns| {
+                cortex_m::asm::delay((time_ns*21)/125 + 1)
+            };
+            enc424j600::SpiEth::new(spi_eth_port, spi1_nss, delay_ns)
         };
 
         // Init
-        match spi_eth.init_dev(&mut delay) {
+        match spi_eth.init_dev() {
             Ok(_) => {
                 iprintln!(stim0, "Initializing Ethernet...")
             }
diff --git a/src/lib.rs b/src/lib.rs
index af883e9..71e6e7c 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -4,7 +4,6 @@ pub mod spi;
 use embedded_hal::{
     blocking::{
         spi::Transfer,
-        delay::DelayUs,
     },
     digital::v2::OutputPin,
 };
@@ -19,7 +18,7 @@ pub mod smoltcp_phy;
 pub const RAW_FRAME_LENGTH_MAX: usize = 1518;
 
 pub trait EthController {
-    fn init_dev(&mut self, delay: &mut impl DelayUs<u16>) -> Result<(), EthControllerError>;
+    fn init_dev(&mut self) -> Result<(), EthControllerError>;
     fn init_rxbuf(&mut self) -> Result<(), EthControllerError>;
     fn init_txbuf(&mut self) -> Result<(), EthControllerError>;
     fn receive_next(&mut self, is_poll: bool) -> Result<rx::RxPacket, EthControllerError>;
@@ -45,17 +44,19 @@ impl From<spi::SpiPortError> for EthControllerError {
 
 /// Ethernet controller using SPI interface
 pub struct SpiEth<SPI: Transfer<u8>,
-                  NSS: OutputPin> {
-    spi_port: spi::SpiPort<SPI, NSS>,
+                  NSS: OutputPin,
+                  F: FnMut(u32) -> ()> {
+    spi_port: spi::SpiPort<SPI, NSS, F>,
     rx_buf: rx::RxBuffer,
     tx_buf: tx::TxBuffer
 }
 
 impl <SPI: Transfer<u8>,
-      NSS: OutputPin> SpiEth<SPI, NSS> {
-    pub fn new(spi: SPI, nss: NSS) -> Self {
+      NSS: OutputPin,
+      F: FnMut(u32) -> ()> SpiEth<SPI, NSS, F> {
+    pub fn new(spi: SPI, nss: NSS, delay_ns: F) -> Self {
         SpiEth {
-            spi_port: spi::SpiPort::new(spi, nss),
+            spi_port: spi::SpiPort::new(spi, nss, delay_ns),
             rx_buf: rx::RxBuffer::new(),
             tx_buf: tx::TxBuffer::new()
         }
@@ -63,8 +64,9 @@ impl <SPI: Transfer<u8>,
 }
 
 impl <SPI: Transfer<u8>,
-      NSS: OutputPin> EthController for SpiEth<SPI, NSS> {
-    fn init_dev(&mut self, delay: &mut impl DelayUs<u16>) -> Result<(), EthControllerError> {
+      NSS: OutputPin,
+      F: FnMut(u32) -> ()> EthController for SpiEth<SPI, NSS, F> {
+    fn init_dev(&mut self) -> Result<(), EthControllerError> {
         // Write 0x1234 to EUDAST
         self.spi_port.write_reg_16b(spi::addrs::EUDAST, 0x1234)?;
         // Verify that EUDAST is 0x1234
@@ -80,15 +82,13 @@ impl <SPI: Transfer<u8>,
         // Set ETHRST (ECON2<4>) to 1
         let econ2 = self.spi_port.read_reg_8b(spi::addrs::ECON2)?;
         self.spi_port.write_reg_8b(spi::addrs::ECON2, 0x10 | (econ2 & 0b11101111))?;
-        // Wait for 25us
-        delay.delay_us(25_u16);
+        self.spi_port.delay_us(25);
         // Verify that EUDAST is 0x0000
         eudast = self.spi_port.read_reg_16b(spi::addrs::EUDAST)?;
         if eudast != 0x0000 {
             return Err(EthControllerError::GeneralError)
         }
-        // Wait for 256us
-        delay.delay_us(256_u16);
+        self.spi_port.delay_us(256);
         Ok(())
     }
 
diff --git a/src/spi.rs b/src/spi.rs
index c2f5dcc..a5dd23c 100644
--- a/src/spi.rs
+++ b/src/spi.rs
@@ -52,9 +52,11 @@ pub mod addrs {
 /// Struct for SPI I/O interface on ENC424J600
 /// Note: stm32f4xx_hal::spi's pins include: SCK, MISO, MOSI
 pub struct SpiPort<SPI: Transfer<u8>,
-                   NSS: OutputPin> {
+                   NSS: OutputPin,
+                   F: FnMut(u32) -> ()> {
     spi: SPI,
     nss: NSS,
+    delay_ns: F,
 }
 
 pub enum SpiPortError {
@@ -63,14 +65,16 @@ pub enum SpiPortError {
 
 #[allow(unused_must_use)]
 impl <SPI: Transfer<u8>,
-      NSS: OutputPin> SpiPort<SPI, NSS> {
+      NSS: OutputPin,
+      F: FnMut(u32) -> ()> SpiPort<SPI, NSS, F> {
     // TODO: return as Result()
-    pub fn new(spi: SPI, mut nss: NSS) -> Self {
+    pub fn new(spi: SPI, mut nss: NSS, delay_ns: F) -> Self {
         nss.set_high();
 
         SpiPort {
             spi,
-            nss
+            nss,
+            delay_ns,
         }
     }
 
@@ -115,6 +119,10 @@ impl <SPI: Transfer<u8>,
         Ok(())
     }
 
+    pub fn delay_us(&mut self, duration: u32) {
+        (self.delay_ns)(duration * 1000)
+    }
+
     // TODO: Generalise transfer functions
     // TODO: (Make data read/write as reference to array)
     // Currently requires 1-byte addr, read/write data is only 1-byte
@@ -131,17 +139,17 @@ impl <SPI: Transfer<u8>,
         match self.spi.transfer(&mut buf) {
             Ok(_) => {
                 // Disable chip select
-                cortex_m::asm::delay(10_u32);
+                (self.delay_ns)(60);
                 self.nss.set_high();
-                cortex_m::asm::delay(5_u32);
+                (self.delay_ns)(30);
                 Ok(buf[2])
             },
             // TODO: Maybe too naive?
             Err(_) => {
                 // Disable chip select
-                cortex_m::asm::delay(10_u32);
+                (self.delay_ns)(60);
                 self.nss.set_high();
-                cortex_m::asm::delay(5_u32);
+                (self.delay_ns)(30);
                 Err(SpiPortError::TransferError)
             }
         }