Made use of the timer to control the time it blinks in microseconds

Author: apinsard

kernel.img

@@ -58,19 +58,32 @@ Disassembly of section .text:
     8098:	e3a00010 	mov	r0, #16	; 0x10
     809c:	e3a01000 	mov	r1, #0	; 0x0
     80a0:	ebffffeb 	bl	8054 <SetGpio>
-    80a4:	e3a0283f 	mov	r2, #4128768	; 0x3f0000
+    80a4:	e3a00001 	mov	r0, #1	; 0x1
+    80a8:	e1a00800 	lsl	r0, r0, #16
+    80ac:	eb000009 	bl	80d8 <Wait>
+    80b0:	e3a00010 	mov	r0, #16	; 0x10
+    80b4:	e3a01001 	mov	r1, #1	; 0x1
+    80b8:	ebffffe5 	bl	8054 <SetGpio>
+    80bc:	e3a00001 	mov	r0, #1	; 0x1
+    80c0:	e1a00980 	lsl	r0, r0, #19
+    80c4:	eb000003 	bl	80d8 <Wait>
+    80c8:	eafffff2 	b	8098 <mainloop$>
 
-000080a8 <wait1$>:
-    80a8:	e2422001 	sub	r2, r2, #1	; 0x1
-    80ac:	e3520000 	cmp	r2, #0	; 0x0
-    80b0:	1afffffc 	bne	80a8 <wait1$>
-    80b4:	e3a00010 	mov	r0, #16	; 0x10
-    80b8:	e3a01001 	mov	r1, #1	; 0x1
-    80bc:	ebffffe4 	bl	8054 <SetGpio>
-    80c0:	e3a0283f 	mov	r2, #4128768	; 0x3f0000
+000080cc <GetCounterValue>:
+    80cc:	e59f0028 	ldr	r0, [pc, #40]	; 80fc <waitLoop$+0x10>
+    80d0:	e1c000d4 	ldrd	r0, [r0, #4]
+    80d4:	e1a0f00e 	mov	pc, lr
 
-000080c4 <wait2$>:
-    80c4:	e2422001 	sub	r2, r2, #1	; 0x1
-    80c8:	e3520000 	cmp	r2, #0	; 0x0
-    80cc:	1afffffc 	bne	80c4 <wait2$>
-    80d0:	eafffff0 	b	8098 <mainloop$>
+000080d8 <Wait>:
+    80d8:	e92d4000 	push	{lr}
+    80dc:	e92d0001 	push	{r0}
+    80e0:	ebfffff9 	bl	80cc <GetCounterValue>
+    80e4:	e8bd0002 	pop	{r1}
+    80e8:	e0802001 	add	r2, r0, r1
+
+000080ec <waitLoop$>:
+    80ec:	ebfffff6 	bl	80cc <GetCounterValue>
+    80f0:	e1500002 	cmp	r0, r2
+    80f4:	9afffffc 	bls	80ec <waitLoop$>
+    80f8:	e8bd8000 	pop	{pc}
+    80fc:	20003000 	.word	0x20003000

kernel.list

@@ -21,6 +21,16 @@ Discarded input sections
  .janus_2cc_veneer
                 0x00000000        0x0 build/main.o
  .v4_bx         0x00000000        0x0 build/main.o
+ .data          0x00000000        0x0 build/timer.o
+ .bss           0x00000000        0x0 build/timer.o
+ .ARM.attributes
+                0x00000000        0x0 build/timer.o
+ .glue_7        0x00000000        0x0 build/timer.o
+ .glue_7t       0x00000000        0x0 build/timer.o
+ .vfp11_veneer  0x00000000        0x0 build/timer.o
+ .janus_2cc_veneer
+                0x00000000        0x0 build/timer.o
+ .v4_bx         0x00000000        0x0 build/timer.o
 
 Memory Configuration
 
@@ -31,19 +41,23 @@ Linker script and memory map
 
 LOAD build/gpio.o
 LOAD build/main.o
+LOAD build/timer.o
 
 .init           0x00008000        0x4
  *(.init)
  .init          0x00008000        0x4 build/main.o
                 0x00008000                _start
 
-.text           0x00008004       0xd0
+.text           0x00008004       0xfc
  *(.text)
  .text          0x00008004       0x84 build/gpio.o
                 0x0000800c                SetGpioFunction
                 0x00008004                GetGpioAddress
                 0x00008054                SetGpio
- .text          0x00008088       0x4c build/main.o
+ .text          0x00008088       0x44 build/main.o
+ .text          0x000080cc       0x34 build/timer.o
+                0x000080cc                GetCounterValue
+                0x000080d8                Wait
 
 /DISCARD/
  *(*)

kernel.map

@@ -26,7 +26,7 @@
 @ == r[1..3]
 GetGpioAddress:
   ldr r0, =GPIO_ADDR
-  mov pc, lr
+  mov pc, lr @ < Return
 
 @
 @ Apply a GPIO function to a pin.

src/gpio.s

@@ -31,12 +31,12 @@ mainloop$:
   .unreq pinNum
   .unreq pinVal
 
-  @ Wait a few time
-  mov r2,#0x3F0000
-  wait1$:
-    sub r2,#1
-    cmp r2,#0
-    bne wait1$
+  @ Wait ~1/20 second
+  nbUsec .req r0
+  mov nbUsec, #1
+  lsl nbUsec, #16
+  bl Wait
+  .unreq nbUsec
 
   @ Turn on the pin to turn off the ACT LED
   pinNum .req r0
@@ -47,12 +47,12 @@ mainloop$:
   .unreq pinNum
   .unreq pinVal
 
-  @ Wait a few time
-  mov r2,#0x3F0000
-  wait2$:
-    sub r2,#1
-    cmp r2,#0
-    bne wait2$
+  @ Wait ~1/2 second
+  nbUsec .req r0
+  mov nbUsec, #1
+  lsl nbUsec, #19
+  bl Wait
+  .unreq nbUsec
 
   b   mainloop$
 

src/main.s

@@ -0,0 +1,48 @@
+@ Distributed under the terms of the GNU General Public License v2
+.globl TIMER_ADDR
+.globl GetCounterValue
+.globl Wait
+
+.equiv TIMER_ADDR       , 0x20003000
+
+@
+@ Load the counter value in memory
+@ => r0: 4 lowest bits
+@ => r1: 4 highest bits
+@ == r[2..3]
+GetCounterValue:
+  counterValLo .req r0
+  counterValHi .req r1
+  ldr r0, =TIMER_ADDR
+  ldrd counterValLo, counterValHi, [r0,#4]
+  mov pc, lr @ < Return
+
+@
+@ Wait for nbUsec microseconds
+@ == r3
+Wait:
+  nbUsec .req r0 @ <- number of microseconds to wait [0, 2^32[
+
+  push {lr}
+
+  @ Retrieve the current value of the counter
+  push {nbUsec}
+  .unreq nbUsec
+  bl GetCounterValue
+  nbUsec .req r1
+  pop {nbUsec}
+  counterVal .req r0
+
+  @ Set the gap to wait
+  gapToWait .req r2
+  add gapToWait, counterVal, nbUsec
+  .unreq nbUsec
+
+  @ And finally, wait
+  waitLoop$:
+    bl GetCounterValue
+    cmp counterVal, gapToWait
+  bls waitLoop$
+
+  pop {pc} @ < Return
+