Only clear uart interrupt when reading status register

Author: object-Object

README.md

@@ -76,7 +76,7 @@ Read/write pointers are stored modulo `capacity + 1`. A buffer is empty when `rp
 
 Note that the processor itself does not prevent code from overflowing the TX buffer. Users are expected to check the Status register and avoid writing too much data at once.
 
-If any UART interrupt is pending, `mip.MEIP` will become pending. To make UART interrupts visible to S-mode, M-mode software must either delegate `mip.MEIP` via `mideleg`, or manually update `mip.SEIP` in an M-mode interrupt handler. The interrupt for a given port is cleared when any register for that port is accessed.
+If any UART interrupt is pending, `mip.MEIP` will become pending. To make UART interrupts visible to S-mode, M-mode software must either delegate `mip.MEIP` via `mideleg`, or manually update `mip.SEIP` in an M-mode interrupt handler. The interrupt for a given port is cleared when the Status register for that port is accessed.
 
 Internally, UART interrupts are implemented using the `uart_flags` variable.
 

src/cpu/worker.mlog.jinja

@@ -809,21 +809,6 @@ access_uart:
 
     op add $$offset $$offset {{UART_RX_OFFSET}}
 
-#% do free_locals("$$uart")
-    # check if interrupt is pending for this port
-    op shl $mask 1 $$uart_shift
-    op and $mask uart_flags $mask
-    jump access_uart__no_clear_ip equal $mask 0
-
-    # clear pending interrupt
-    op not $mask $mask
-    op and uart_flags uart_flags $mask
-
-    # set interrupt_flags.poll
-    op or csr_mip csr_mip 0b10000000000000000000000000000000
-#% do declare_locals(access_uart_locals)
-access_uart__no_clear_ip:
-
     op add $$uart $$uart_shift {{UART_START_LINK}}
     getlink $$uart $$uart
 
@@ -1052,7 +1037,7 @@ load_mmio_word__not_zero:
 
 load_mmio_word__uart_status:
 #% do declare_locals(access_uart_locals)
-#% do free_locals("$$offset")
+#% do free_locals("$$offset", "$$uart")
     # interrupt enabled
     op shr result uart_flags $$uart_shift
     op and result result 0b10000
@@ -1079,6 +1064,19 @@ load_mmio_word__uart_status__rx_empty:
     op or result result 0b00010
 load_mmio_word__uart_status__rx_not_full:
 
+    # check if interrupt is pending for this port
+    op shl $mask 1 $$uart_shift
+    op and $mask uart_flags $mask
+    jump load_mmio_word__uart_status__no_clear_interrupt equal $mask 0
+
+    # clear pending interrupt
+    op not $mask $mask
+    op and uart_flags uart_flags $mask
+
+    # set interrupt_flags.poll
+    op or csr_mip csr_mip 0b10000000000000000000000000000000
+load_mmio_word__uart_status__no_clear_interrupt:
+
     set @counter ret
 
 # instruction decoder