From a639316cdf7b7f08f623b90828c29c6f01c1681b Mon Sep 17 00:00:00 2001
From: Martin Preuss <martin@aquamaniac.de>
Date: Thu, 16 Jan 2025 17:05:07 +0100
Subject: [PATCH] avr: added code for fixed buffers.

---
 avr/common/0BUILD           |   1 +
 avr/common/fixedbuffers.asm | 112 ++++++++++++++++++++++++++++++++++++
 2 files changed, 113 insertions(+)
 create mode 100644 avr/common/fixedbuffers.asm

diff --git a/avr/common/0BUILD b/avr/common/0BUILD
index dacfbb9..67ae26b 100644
--- a/avr/common/0BUILD
+++ b/avr/common/0BUILD
@@ -4,6 +4,7 @@
 
   <extradist>
     crc8.asm
+    fixedbuffers.asm
     m_ringbuffer.asm
     m_ringbuffer_y.asm
     ringbuffer.asm
diff --git a/avr/common/fixedbuffers.asm b/avr/common/fixedbuffers.asm
new file mode 100644
index 0000000..3ad19d2
--- /dev/null
+++ b/avr/common/fixedbuffers.asm
@@ -0,0 +1,112 @@
+; ***************************************************************************
+; copyright   : (C) 2025 by Martin Preuss
+; email       : martin@libchipcard.de
+;
+; ***************************************************************************
+; * This file is part of the project "AqHome".                              *
+; * Please see toplevel file COPYING of that project for license details.   *
+; ***************************************************************************
+
+
+; ---------------------------------------------------------------------------
+; @macro m_fixedbuf_init
+;
+; @param X pointer to start of buffers
+; @param %0 constant maxBytes per buffer (including statusbyte in front)
+; @param %1 constant maxBuffers
+; @clobbers r16, r17, X
+
+.macro m_fixedbuf_init
+  ldi r17, @1
+  clr r16
+l_loop:
+    st X, r16 ; unused
+    adiw xh:xl,@0
+    dec r17
+  brne l_loop
+.endmacro
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @macro m_fixedbuf_reserve
+;
+; @return CFLAG set if buffer available, cleared otherwise
+; @return r16 buffer num
+; @return X pointer to start of buffer
+; @param X pointer to start of buffers
+; @param %0 constant maxBytes per buffer (including statusbyte in front)
+; @param %1 constant maxBuffers
+; @clobbers r16, r17, X
+
+.macro m_fixedbuf_reserve
+  clr r17              ; loop var: current buffer num
+l_loop:
+    ld r16, X
+    tst r16
+    breq l_foundfree
+    adiw xh:xl, @0
+    inc r17
+    cpi r17, @1
+  brcs l_loop
+  rjmp l_end           ; use cleared CFLAG
+l_foundfree:
+  ldi r16, 0x80        ; mark as used
+  st X, r16
+  mov r16, r17
+  sec                  ; set CFLAG, return bufnum in r16, pointre in X
+l_end:
+.endmacro
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @macro m_fixedbuf_release
+;
+; @param X pointer to start of buffers
+; @param %0 constant maxBytes per buffer (including statusbyte in front)
+; @param %1 constant maxBuffers
+; @clobbers r16
+
+.macro m_fixedbuf_release
+  clr r16
+  st X, r16
+.endmacro
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @macro m_fixedbuf_locate
+;
+; use this routine only if you can't easily calculate the offset of the buffer
+; (e.g. by using shift operations for calculation)
+;
+; @return CFLAG set if buffer found, cleared otherwise
+; @return X pointer to start of located buffer (points to the statusbyte in front)
+; @param r16 buffer num
+; @param X pointer to start of buffers
+; @param %0 constant maxBytes per buffer
+; @param %1 constant maxBuffers
+; @clobbers r16, X
+
+.macro m_fixedbuf_locate:
+  cpi r16, @1
+  brcc l_end          ; idx out of range, use cleared CFLAG
+  tst r16             ; doesn't change CFLAG which is set from CPI above
+  breq l_end          ; buffer 0, return start of buffers
+l_loop:
+    adiw xh:xl, @0
+    dec r16
+  brne l_loop
+  sec
+l_end:
+.endmacro
+; @end
+
+
+
+
+