From 2953b35cea6515a5de73bba798583bbb4146bdce Mon Sep 17 00:00:00 2001
From: "B. Watson" <urchlay@slackware.uk>
Date: Mon, 6 Apr 2026 07:28:16 -0400
Subject: Rewrite txbuf_append_chr() in asm. 6795 bytes free.

---
 src/main.c  |  4 ----
 src/txbuf.s | 29 +++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+), 4 deletions(-)
 create mode 100644 src/txbuf.s

diff --git a/src/main.c b/src/main.c
index 318654d..66ced7f 100644
--- a/src/main.c
+++ b/src/main.c
@@ -29,10 +29,6 @@ char reconnect_timeout = 1;
 
 extern void ih();               // defined in intr.s
 
-void txbuf_append_chr(char c) {
-	tx_buf[txbuflen++] = c;
-}
-
 void txbuf_init(void) {
 	txbuflen = tx_buf[0] = 0;
 }
diff --git a/src/txbuf.s b/src/txbuf.s
new file mode 100644
index 0000000..4783660
--- /dev/null
+++ b/src/txbuf.s
@@ -0,0 +1,29 @@
+;; void txbuf_append_chr(char c) {
+;; 	tx_buf[txbuflen++] = c;
+;; }
+
+; compiles to 45 bytes. routine below is 29 bytes (~33% smaller)
+
+ tx_buf = $a200 ; MUST agree with src/rxtxbuf.h!
+
+ .import _txbuflen
+ .export _txbuf_append_chr
+ .importzp sreg ; avoid ptr1 & friends, callers may use
+
+_txbuf_append_chr:
+ tax
+ lda #<tx_buf
+ clc
+ adc _txbuflen
+ sta sreg
+ lda #>tx_buf
+ adc _txbuflen+1
+ sta sreg+1
+ ldy #0
+ txa
+ sta (sreg),y
+ inc _txbuflen
+ bne @ret
+ inc _txbuflen+1
+@ret:
+ rts
-- 
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