From 40710a003ad55124d57bd52330cd90ce6afbae2b Mon Sep 17 00:00:00 2001
From: Martin Preuss <martin@aquamaniac.de>
Date: Sat, 4 Feb 2023 16:00:50 +0100
Subject: [PATCH] Utils: Added pseudo random generator.

---
 avr/utils.asm | 185 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 185 insertions(+)

diff --git a/avr/utils.asm b/avr/utils.asm
index 60f361b..0ea7d23 100644
--- a/avr/utils.asm
+++ b/avr/utils.asm
@@ -1,5 +1,9 @@
 
 
+; ***************************************************************************
+; macros
+
+
 
 ; ---------------------------------------------------------------------------
 ; Utils_WaitNanoSecs  waittime_in_ns , cyles_already_used , waitcount_register 
@@ -42,6 +46,81 @@
 
 
 
+; ***************************************************************************
+; data
+
+
+.dseg
+
+utilsDataBegin:
+  utilsSeed:     .byte 2
+utilsDataEnd:
+
+
+
+; ***************************************************************************
+; code
+
+
+.cseg
+
+utilsDateString:    .db "%YEAR%-%MONTH%-%DAY%-%HOUR%:%MINUTE%", 0, 0
+
+
+
+
+; ---------------------------------------------------------------------------
+; Utils_Init
+;
+; IN:
+; OUT:
+; - CFLAG: set if okay, clear on error
+; USED: R16, R17, R18, X, Y
+
+Utils_Init:
+  ; preset SRAM data area
+  ldi xh, HIGH(utilsDataBegin)
+  ldi xl, LOW(utilsDataBegin)
+  clr r16
+  ldi r17, (utilsDataEnd-utilsDataBegin)
+  rcall Utils_FillSram
+
+  ; generate initial seed from compile date string
+  ldi zl, LOW(utilsDateString*2)
+  ldi zh, HIGH(utilsDateString*2)
+  ldi r18, 0xe1
+  ldi r19, 0xac
+Utils_Init_l1:
+    lpm r16, Z+
+    tst r16
+    breq Utils_Init_l2
+    eor r18, r16
+    lsl r18
+    rol r19
+  rjmp Utils_Init_l1
+Utils_Init_l2:
+  sts utilsSeed, r18
+  sts utilsSeed+1, r19
+
+  sec
+  ret
+
+
+
+; ---------------------------------------------------------------------------
+; Utils_Fini
+;
+; IN:
+; OUT:
+; - CFLAG: set if okay, clear on error
+; USED: R16, R17, R18, X, Y
+
+
+Utils_Fini:
+  sec
+  ret
+
+
 
 ; ---------------------------------------------------------------------------
 ; Utils_FillSram
@@ -263,3 +342,109 @@ wait:                ; wait for possibly previous SPM to complete
 
 
 
+; ---------------------------------------------------------------------------
+; Utils_PseudoRandom
+;
+; Generate a pseudo random number.
+; (see https://www.avrfreaks.net/s/topic/a5C3l000000URNfEAO/t119045?comment=P-1021038)
+;
+; IN:
+; OUT:
+; - R16: 8 bit pseudo random number
+; REGS: R16, R17, R18, R19
+
+Utils_PseudoRandom:
+  lds r16, utilsSeed
+  lds r17, utilsSeed+1
+  ldi r18, 0x9c
+  ldi r19, 8
+Utils_PseudoRandom_step:
+  lsr   r17
+  ror   r16
+  brcc  Utils_PseudoRandom_nomask
+  eor   r17,    r18
+Utils_PseudoRandom_nomask:
+  dec   r19
+  brne  Utils_PseudoRandom_step
+  sts utilsSeed, r16
+  sts utilsSeed+1, r17
+  ret                    ; result in r16
+
+
+
+; ---------------------------------------------------------------------------
+; Utils_ReadUid
+;
+; Read UID from EEPROM.
+;
+; IN:
+; OUT:
+; - R18:R19:R20:R21: UID
+; REGS: R16, X
+
+Utils_ReadUid:
+  push r15
+    in r15, SREG
+    cli
+    ldi xl, LOW(EEPROM_OFFS_UUID)
+    ldi xh, HIGH(EEPROM_OFFS_UUID)
+    rcall Utils_ReadEeprom ; (R16)
+    mov r18, r16
+    adiw xh:xl, 1
+    rcall Utils_ReadEeprom ; (R16)
+    mov r19, r16
+    adiw xh:xl, 1
+    rcall Utils_ReadEeprom ; (R16)
+    mov r20, r16
+    adiw xh:xl, 1
+    rcall Utils_ReadEeprom ; (R16)
+    mov r21, r16
+  pop r15
+  out SREG, r15
+  ret
+
+
+
+; ---------------------------------------------------------------------------
+; Utils_SetupUid
+;
+; Reads UID from EEPROM. If not set generate a new one and store it in EEPROM.
+;
+; IN:
+; OUT:
+; - CFLAG set if new generated, cleared if there already was one.
+; REGS: R15, R16, R18, R19, R20, R21, X
+
+Utils_SetupUid:
+  in r15, SREG
+  cli
+  rcall Utils_ReadUid          ; R16, X
+  mov r16, r18                 ; all 0xff?
+  or r16, r19
+  or r16, r20
+  or r16, r21
+  breq Utils_SetupUid_generate ; yep, go generate one
+  out SREG, r15
+  clc
+  ret
+Utils_SetupUid_generate:
+  ldi xl, LOW(EEPROM_OFFS_UUID)
+  ldi xh, HIGH(EEPROM_OFFS_UUID)
+  rcall Utils_PseudoRandom      ; byte 0 (R16, R17, R18, R19)
+  inc r16
+  rcall Utils_WriteEeprom       ; (R17)
+  adiw xh:xl, 1
+  rcall Utils_PseudoRandom      ; byte 1
+  rcall Utils_WriteEeprom
+  adiw xh:xl, 1
+  rcall Utils_PseudoRandom      ; byte 2
+  rcall Utils_WriteEeprom
+  adiw xh:xl, 1
+  rcall Utils_PseudoRandom      ; byte 3
+  rcall Utils_WriteEeprom
+  adiw xh:xl, 1
+  out SREG, r15
+  sec
+  ret
+
+