Fix UART bugs

6 files changed, 67 insertions, 81 deletions

diff --git a/Makefile b/Makefile
index bc5bc31..3529884 100644
--- a/Makefile
+++ b/Makefile
@@ -1,17 +1,17 @@
 all: build
 
-build: blink.uf2
+build: echo.uf2
 
-blink.uf2: blink.elf
-	./elf2uf2 blink.elf blink.uf2
+echo.uf2: echo.elf
+	./elf2uf2 echo.elf echo.uf2
 
-objects = main.o blink.o clocks.o gpio.o pll.o uart.o xosc.o
+objects = main.o xosc.o clocks.o gpio.o uart.o
 
-blink.elf: $(objects)
-	arm-none-eabi-ld -T pico_ram_only.ld -o blink.elf $(objects)
+echo.elf: $(objects)
+	arm-none-eabi-ld -T pico_ram_only.ld -o echo.elf $(objects)
 
 $(objects): %.o: %.s
 	arm-none-eabi-as -o $@ $<
 
 clean:
-	rm blink.elf blink.uf2 *.o
+	rm echo.elf echo.uf2 *.o
diff --git a/clocks.s b/clocks.s
index 74bd215..83bc9ff 100644
--- a/clocks.s
+++ b/clocks.s
@@ -3,16 +3,29 @@
 .thumb
 
 .equ CLOCKS_BASE, 0x40008000
-.equ CLK_REF_CTRL_OFST, 0x30
-.equ CLK_SYS_CTRL_OFST, 0x3c
+.equ CLK_REF_CTRL_OFST,  0x30
+.equ CLK_SYS_CTRL_OFST,  0x3c
+.equ CLK_PERI_CTRL_OFST, 0x48
 
 .type setup_clocks, %function
 .global setup_clocks
 
 setup_clocks:
+
   ldr r1, =CLOCKS_BASE
-  movs r0, 2 // use xosc (=0x2) as clk_ref source
+
+  // Reference clock
+  movs r0, 0x2 // src = xosc
   str r0, [r1, CLK_REF_CTRL_OFST]
-  movs r0, 1 // use auxsrc (default pll_sys, =0x1) as clk_sys source
+
+  // System clock
+  movs r0, 0x0 // src = clk_ref
   str r0, [r1, CLK_SYS_CTRL_OFST]
+
+  // Peripheral clock
+  movs r0, 1 // set enable
+  lsls r0, 11
+  adds r0, 0x4 << 5 // src = xosc
+  str r0, [r1, CLK_PERI_CTRL_OFST]
+
   bx lr
diff --git a/gpio.s b/gpio.s
index 1ef296c..32e2c37 100644
--- a/gpio.s
+++ b/gpio.s
@@ -2,7 +2,7 @@
 .cpu cortex-m0plus
 .thumb
 
-.equ RESETS_BASE,     0x4000c000
+.equ RESETS_BASE, 0x4000c000
 .equ RESET_OFST,      0x0
 .equ RESET_DONE_OFST, 0x8
 
@@ -12,14 +12,12 @@
 .global setup_gpio
 
 setup_gpio:
-  // clear reset
   ldr r1, =(RESETS_BASE + ATOMIC_CLEAR)
-  movs r0, 0x20 // IO_BANK0 is bit 5
+  movs r0, 0b1 << 5 // IO_BANK0
   str r0, [r1, RESET_OFST]
   ldr r1, =RESETS_BASE
 1:
   ldr r2, [r1, RESET_DONE_OFST]
-  tst r0, r2 // IO_BANK0 is still bit 5
-  // wait for reset done
+  tst r2, r0
   beq 1b
   bx lr
diff --git a/main.s b/main.s
index 8f72dfe..5e294d4 100644
--- a/main.s
+++ b/main.s
@@ -7,8 +7,10 @@
 
 main:
   bl start_xosc
-  bl start_pll
   bl setup_clocks
   bl setup_gpio
-  bl setup_led
-  b led_on
+  bl setup_uart
+1:
+  bl uart_recv
+  bl uart_send
+  b 1b
diff --git a/uart.s b/uart.s
index c2af3b3..19a2882 100644
--- a/uart.s
+++ b/uart.s
@@ -2,86 +2,59 @@
 .cpu cortex-m0plus
 .thumb
 
-.equ RESETS_BASE,     0x4000c000
+.equ RESETS_BASE, 0x4000c000
 .equ RESET_OFST,      0x0
 .equ RESET_DONE_OFST, 0x8
 
-.equ CLOCKS_BASE, 0x40008000
-.equ CLK_REF_CTRL_OFST, 0x30
-.equ CLK_SYS_CTRL_OFST, 0x3c
-.equ CLK_PERI_CTRL_OFST, 0x48
-
-.equ UART0_BASE, 0x40034000
-.equ UARTDR_OFST, 0x00
-.equ UARTFR_OFST, 0x18
-.equ UARTIBRD_OFST, 0x24
-.equ UARTFBRD_OFST, 0x28
-.equ UARTLCR_H_OFST, 0x2c
-.equ UARTCR_OFST, 0x30
-
 .equ IO_BANK0_BASE, 0x40014000
 .equ GPIO0_CTRL_OFST, 0x04
 .equ GPIO1_CTRL_OFST, 0x0c
 
+.equ UART0_BASE, 0x40034000
+.equ UARTDR_OFST,     0x00
+.equ UARTFR_OFST,     0x18
+.equ UARTIBRD_OFST,   0x24
+.equ UARTFBRD_OFST,   0x28
+.equ UARTLCR_H_OFST,  0x2c
+.equ UARTCR_OFST,     0x30
+
 .equ ATOMIC_SET,    0x2000
-.equ ATOMIC_CLEAR,    0x3000
+.equ ATOMIC_CLEAR,  0x3000
 
 .type setup_uart, %function
 .global setup_uart
 
 setup_uart:
 
-  // Enable clk_peri
-  movs r0, 0x1 // set enable bit (0x1 << 11)
-  lsls r0, 11
-  movs r1, 0x4 // use xosc (=0x4 << 5) as clk_ref source
-  lsls r1, 5
-  orrs r0, r1
-  ldr r1, =CLOCKS_BASE
-  str r0, [r1, CLK_PERI_CTRL_OFST]
-
-  // Reset UART0
-  movs r0, 1
-  lsls r0, r0, 22 // UART0 is bit 22
-
-  // Assert the reset
-  ldr r1, =(RESETS_BASE + ATOMIC_SET)
-  str r0, [r1, RESET_OFST]
-
-  // Deassert the reset
+  // Deassert reset
   ldr r1, =(RESETS_BASE + ATOMIC_CLEAR)
+  movs r0, 0b1 // UART0
+  lsls r0, 22
   str r0, [r1, RESET_OFST]
-
-  // Check if reset done
   ldr r1, =RESETS_BASE
 1:
   ldr r2, [r1, RESET_DONE_OFST]
-  tst r0, r2
+  tst r2, r0
   beq 1b
 
-  // Configure GPIO 0 and 1 as UART0
+  // Configure and enable
+  ldr r1, =UART0_BASE
+  movs r0, 6
+  str r0, [r1, UARTIBRD_OFST]
+  movs r0, 33
+  str r0, [r1, UARTFBRD_OFST]
+  movs r0, 0b111 << 4 // 0b11 = word len 8 bits, 0b1 = FIFO enabled
+  str r0, [r1, UARTLCR_H_OFST]
+  ldr r1, =(UART0_BASE + ATOMIC_SET)
+  movs r0, 0b1 // UART enable
+  str r0, [r1, UARTCR_OFST]
+
+  // Configure GPIO 0 and 1 as TX and RX
   ldr r1, =IO_BANK0_BASE
-  movs r0, 2 // UART function = 2
+  movs r0, 2 // UART function
   str r0, [r1, GPIO0_CTRL_OFST]
   str r0, [r1, GPIO1_CTRL_OFST]
 
-  // Set the baud rate divisors
-  movs r0, 6 // integer baud rate = 6
-  ldr r0, [r1, UARTIBRD_OFST]
-  movs r0, 33 // fractional baud rate = 33
-  ldr r0, [r1, UARTFBRD_OFST]
-
-  // Enable the FIFOs and set the format
-  movs r0, 0x70 // word len 8 bits (bits 6:5 = 0b11), bit 4 (FIFO en)
-  str r0, [r1, UARTLCR_H_OFST]
-
-  // Set enable bits in the control register
-  ldr r1, =UART0_BASE
-  movs r0, 0x3
-  lsls r0, 8 // set bits 8 and 9 (TX and RX enable)
-  adds r0, 0x1 // set bit 0 (UART enable)
-  str r0, [r1, UARTCR_OFST]
-
   bx lr
 
 .type uart_send, %function
@@ -89,11 +62,11 @@ setup_uart:
 
 uart_send:
   ldr r1, =UART0_BASE
-poll_TXFF:
+1:
   ldr r2, [r1, UARTFR_OFST]
-  movs r3, 0x20 // bit 5 (TX FIFO full)
+  movs r3, 0b1 << 5 // TX FIFO full
   tst r2, r3
-  bne poll_TXFF
+  bne 1b
   movs r2, 0xff
   ands r0, r2
   str r0, [r1, UARTDR_OFST]
@@ -104,10 +77,10 @@ poll_TXFF:
 
 uart_recv:
   ldr r1, =UART0_BASE
-poll_RXFE:
+1:
   ldr r2, [r1, UARTFR_OFST]
-  movs r3, 0x10 // bit 4 (RX FIFO empty)
+  movs r3, 0b1 << 4 // RX FIFO empty
   tst r2, r3
-  bne poll_RXFE
+  bne 1b
   ldr r0, [r1, UARTDR_OFST]
   bx lr
diff --git a/xosc.s b/xosc.s
index acfc577..883200f 100644
--- a/xosc.s
+++ b/xosc.s
@@ -18,6 +18,6 @@ start_xosc:
   str r0, [r1, CTRL_OFST]
 1:
   ldr r0, [r1, STATUS_OFST]
-  lsrs r0, r0, 31 // poll status bit
+  lsrs r0, 31 // stable bit
   beq 1b
   bx lr