Microcomputertechnik lecture 6.5

Signed-off-by: Aaron Erhardt <aaron.erhardt@t-online.de>

Mikrocomputertechnik/asm.md

+# Assembler
+
+## Arithmetic
+
+### Add
+
+```asm
+add r0, r1, r2 ; ro = r1 + r2
+add r0, r1     ; ro = r0 + r1
+add r0, #1     ; ro = r0 + 1, for small constants
+```
+
+Set flags while adding
+
+```asm
+adds r0, r1, r2 ; ro = r1 + r2, also sets flags
+```
+
+### Subtract
+
+```asm
+sub r0, r1, r2 ; ro = r1 - r2
+```
+
+### Multiply
+
+```asm
+mul r0, r1, r2 ; ro = r1 * r2
+```
+
+### Divide
+
+```asm
+udiv r0, r1, r2 ; ro = r1 / r2, unsigned divide, always rounds down
+```
+
+## Logic
+
+### And
+
+```asm
+and r0, r1, r2 ; ro = r1 AND r2
+```
+
+### OR
+
+```asm
+orr r0, r1, r2 ; ro = r1 OR r2
+```
+
+### Exclusive or
+
+```asm
+eor r0, r1, r2 ; ro = r1 XOR r2
+```
+
+
+## Shift
+
+### Arithmetic shift right
+
+```asm
+asr r0, r1, r2 ; ro = r1 >> r2, keeps correct sign!
+```
+
+### Logical shift right
+
+```asm
+lsr r0, r1, r2 ; ro = r1 >> r2, fills with zeros and doesn't keep correct sign!
+```
+
+### Logical shift left
+
+```asm
+lsl r0, r1, r2 ; ro = r1 << r2, fills with zeros
+```
+
+### Rotate right
+
+```asm
+ror r0, r1, r2 ; ro = r1 >> r2, bits will wrap around
+```
+
 ## Load
 
 ```asm
@@ -15,25 +98,20 @@ MAX DCD 10
 ldr   r3, MAX
 ```
 
-## Move
-
-```asm
-mov r0, r1     ; r0 := r1
-mov rd, #const ; const max. 16-Bit, otherwise load
-```
-
-## Add
+### Store
 
 ```asm
-add r0, r1, r2 ; ro = r1 + r2
-add r0, r1     ; ro = r0 + r1
-add r0, #1     ; ro = r0 + 1, for small constants
+str r1, [r0]      ; store content of r1 into address of r0 
+str r1, [r0, #8]  ; same with offset
+str r1, [r0], #8  ; post-increment
+str r1, [r0, #8]! ; pre-increment
 ```
 
-Set flags while adding
+## Move
 
 ```asm
-adds r0, r1, r2 ; ro = r1 + r2, also sets flags
+mov r0, r1     ; r0 := r1
+mov rd, #const ; const max. 16-Bit, otherwise load
 ```
 
 ## Compare
@@ -92,7 +170,7 @@ push {lr, r3, r10-12} ; push lr, r3 and r10-r12
 pop  {lr, r3, r10-12} ; pop lr, r3 and r10-r12
 ```
 
-# Subroutines
+## Subroutines
 
 ```asm
 main
@@ -157,3 +235,92 @@ add_nums
     pop {lr, r0-r2}
     bx lr
 ```
+
+
+# IO
+
+IO is memory mapped, it is read and set just like a block of memory.
+
+## Typical register types
+
++ Control register (set behavior)
++ Status register
++ Data register
+
+## STM32
+
+### RCC (Reset and Control Logic)
+
+Used to explicitly turn on other I/O blocks by setting bits in the registers.
+
+### GPIO (General Purpose I/O)
+
+Configuration: 
+
++ Set RCC bits to enable I/O block
++ Set pins as input, output, alternate function (reserve pin for other I/O blocks) or analog with two bits in the MODER register
++ Adjust edge steepness (Flankensteilheit) with two bits in the OSPEEDR register
++ Set pull up resistance to NONE, UP or DOWN with two bits in the PUPDR register
+
+Output: Set bits of the ODR register to activate individual pins
+ 
+Input: Read bits of the IDR register to get values of individual pin
+
+**Example**
+
+```asm
+; define port addresses and register offsets (data sheet)...
+
+InitOutputPortB
+    push {r0, r3, r4, lr}
+
+    ; Enable I/O block for PortB
+    ldr r3, = RCC          ; Load start address of RCC registers into r3
+    ldr r0, [r3, #AHB1ENR] ; Load current register values
+    orr r0, r0, #IOPBEN    ; Use logical OR to enable the bit for GPIOBEN and leave the rest unchanged
+    str r0, [r3, #AHB1ENR] ; Store value into the register to enable I/O on PortB
+
+    ; Configure PortB
+    ldr r3, = GPIOB        ; Load start address of GPIOB registers into r3
+    ldr r0, = 0x00005555   ; Load values for configuring the MODER register, using 0x5 = 01_01 to set all pins as output
+    str r0, [r3, #MODER]   ; Store value into the register to enable configuration
+
+    ; Turn on LEDs
+    ldr r0, #3             ; Set first to bits
+    str r0, [r3, #ODR]     ; Load value into ODR register to enable the first to outputs (LEDs)
+
+    pop {r0, r3, r4, lr}
+```
+
+
+### Systick timer
+
+Counts down from a start value until it reaches zero. Then is sets a flag, invokes an interrupt, resets the start value and counts down again.
+
+STK_CTRL register:
+
++ COUNTFLAG: counter has reached zero
++ CLKSOURCE: select counter clock
++ TICKINT: enable interrupt
++ ENABLE: enable counter
+
+STK_LOAD register: 24 bit reset value
+
+STK_VAL register: current counter value
+
+
+### Capture/Compare-Timer
+
+CR1 register: configure timer
+
+CNT register: counter value
+
+ARR register: reset value
+
+PSC register: pre-scale value, divide clock frequency
+
+CCR1-CCR4 registers: 
+
++ compare with counter value and set output pin if counter surpasses the control value
++ on input (e. g. rising edge) capture the current counter value
+