diff --git a/src/zynq/flash/mod.rs b/src/zynq/flash/mod.rs
index 7f678542..92de431c 100644
--- a/src/zynq/flash/mod.rs
+++ b/src/zynq/flash/mod.rs
@@ -17,7 +17,9 @@ const INST_RDCR: u8 = 0x35;
 /// Instruction: Read Identification
 const INST_RDID: u8 = 0x9F;
 
+/// Memory-mapped mode
 pub struct LinearAddressing;
+/// Manual I/O mode
 pub struct Manual;
 
 /// Flash Interface Driver
diff --git a/src/zynq/flash/regs.rs b/src/zynq/flash/regs.rs
index 4f9fb800..01a50ea4 100644
--- a/src/zynq/flash/regs.rs
+++ b/src/zynq/flash/regs.rs
@@ -79,9 +79,13 @@ register_bit!(config,
 
 register!(intr_status, IntrStatus, RW, u32);
 register_bit!(intr_status, rx_overflow, 0);
-register_bit!(intr_status, tx_fifo_not_full, 2);
+register_bit!(intr_status,
+              /// < tx_thres
+              tx_fifo_not_full, 2);
 register_bit!(intr_status, tx_fifo_full, 3);
-register_bit!(intr_status, rx_fifo_not_empty, 4);
+register_bit!(intr_status,
+              /// >= rx_thres
+              rx_fifo_not_empty, 4);
 register_bit!(intr_status, rx_fifo_full, 5);
 register_bit!(intr_status, tx_fifo_underflow, 6);