diff --git a/sys/riscv/include/intr.h b/sys/riscv/include/intr.h
index 57d5e5db1b2..bc8c138ad01 100644
--- a/sys/riscv/include/intr.h
+++ b/sys/riscv/include/intr.h
@@ -60,6 +60,8 @@ enum {
 	IRQ_SOFTWARE,
 	IRQ_TIMER,
 	IRQ_HTIF,
+	IRQ_COP,	/* lowRISC only */
+	IRQ_UART,	/* lowRISC only */
 	NIRQS
 };
 
diff --git a/sys/riscv/include/riscvreg.h b/sys/riscv/include/riscvreg.h
index b411e1824f6..a71ee47e83f 100644
--- a/sys/riscv/include/riscvreg.h
+++ b/sys/riscv/include/riscvreg.h
@@ -47,7 +47,8 @@
 #define	ECALL_SEND_IPI		0x07
 #define	ECALL_CLEAR_IPI		0x08
 #define	ECALL_HTIF_LOWPUTC	0x09
-#define	ECALL_MIE_SET		0x10
+#define	ECALL_MIE_SET		0x0a
+#define	ECALL_IO_IRQ_MASK	0x0b
 
 #define	EXCP_SHIFT			0
 #define	EXCP_MASK			(0xf << EXCP_SHIFT)
@@ -119,6 +120,7 @@
 
 #define	NCSRS		4096
 #define	CSR_IPI		0x783
+#define	CSR_IO_IRQ	0x7c0	/* lowRISC only? */
 #define	XLEN		8
 #define	INSN_SIZE	4
 
diff --git a/sys/riscv/riscv/exception.S b/sys/riscv/riscv/exception.S
index f1f127a4b6a..54f4c76aadc 100644
--- a/sys/riscv/riscv/exception.S
+++ b/sys/riscv/riscv/exception.S
@@ -270,18 +270,27 @@ supervisor_trap:
 machine_interrupt:
 	/* Type of interrupt ? */
 	csrr	t0, mcause
-	andi	t0, t0, 3
+	andi	t0, t0, EXCP_MASK
 	li	t1, 0
 	beq	t1, t0, software_interrupt
 	li	t1, 1
 	beq	t1, t0, timer_interrupt
 	li	t1, 2
 	beq	t1, t0, htif_interrupt
+	li	t1, 4
+	beq	t1, t0, io_interrupt	/* lowRISC only */
 
 	/* not reached */
 1:
 	j	1b
 
+io_interrupt:
+	/* Disable IO interrupts so we can go to supervisor mode */
+	csrwi	CSR_IO_IRQ, 0
+
+	/* Handle the trap in supervisor mode */
+	j	exit_mrts
+
 software_interrupt:
 	li	t0, MIP_MSIP
 	csrc	mip, t0
@@ -307,7 +316,7 @@ software_interrupt:
 	j	exit
 
 1:
-	/* Serve a trap in supervisor mode */
+	/* Handle the trap in supervisor mode */
 	j	exit_mrts
 
 timer_interrupt:
@@ -415,6 +424,12 @@ supervisor_call:
 	beq	t5, t4, htif_lowputc
 	li	t4, ECALL_MIE_SET
 	beq	t5, t4, mie_set
+	li	t4, ECALL_IO_IRQ_MASK
+	beq	t5, t4, io_irq_mask
+	j	exit_next_instr
+
+io_irq_mask:
+	csrw	CSR_IO_IRQ, t6
 	j	exit_next_instr
 
 mie_set:
diff --git a/sys/riscv/riscv/intr_machdep.c b/sys/riscv/riscv/intr_machdep.c
index 5ed109fa519..ad30bf2f991 100644
--- a/sys/riscv/riscv/intr_machdep.c
+++ b/sys/riscv/riscv/intr_machdep.c
@@ -101,6 +101,9 @@ riscv_mask_irq(void *source)
 	case IRQ_SOFTWARE:
 		csr_clear(sie, SIE_SSIE);
 		break;
+	case IRQ_UART:
+		machine_command(ECALL_IO_IRQ_MASK, 0);
+		break;
 	default:
 		panic("Unknown irq %d\n", irq);
 	}
@@ -120,6 +123,9 @@ riscv_unmask_irq(void *source)
 	case IRQ_SOFTWARE:
 		csr_set(sie, SIE_SSIE);
 		break;
+	case IRQ_UART:
+		machine_command(ECALL_IO_IRQ_MASK, 1);
+		break;
 	default:
 		panic("Unknown irq %d\n", irq);
 	}
@@ -203,6 +209,7 @@ riscv_cpu_intr(struct trapframe *frame)
 	active_irq = (frame->tf_scause & EXCP_MASK);
 
 	switch (active_irq) {
+	case IRQ_UART:
 	case IRQ_SOFTWARE:
 	case IRQ_TIMER:
 		event = intr_events[active_irq];