From 86b72b11d6abcc602a93aa480f27644cc0b34373 Mon Sep 17 00:00:00 2001
From: Jacques Comeaux <jacquesrcomeaux@protonmail.com>
Date: Wed, 29 May 2024 08:15:09 -0500
Subject: Use absolute branches for subroutine calls

---
 assembler/uart.s | 107 ++++++++++++++++++++++++++++---------------------------
 1 file changed, 55 insertions(+), 52 deletions(-)

(limited to 'assembler/uart.s')

diff --git a/assembler/uart.s b/assembler/uart.s
index b845c8b..8dd6a68 100644
--- a/assembler/uart.s
+++ b/assembler/uart.s
@@ -7,59 +7,62 @@
 .equ UARTFR_OFST,     0x18
 
 .type uart_send, %function
-.global uart_send
-
-uart_send:
-  ldr r1, =UART0_BASE
-  movs r3, 0b1 << 5 // TX FIFO full
-1:
-  ldr r2, [r1, UARTFR_OFST]
-  tst r2, r3
-  bne 1b
-  strb r0, [r1, UARTDR_OFST]
-  bx lr
-
 .type uart_recv, %function
-.global uart_recv
-
-uart_recv:
-  ldr r1, =UART0_BASE
-  movs r3, 0b1 << 4 // RX FIFO empty
-1:
-  ldr r2, [r1, UARTFR_OFST]
-  tst r2, r3
-  bne 1b
-  ldrb r0, [r1, UARTDR_OFST]
-  bx lr
-
+.type get_char, %function
 .type send_hex, %function
+
+.global uart_send
+.global uart_recv
+.global get_char
 .global send_hex
 
-send_hex:
-  push {lr}
-  movs r4, r0
-  movs r0, '0
-  bl uart_send
-  movs r0, 'x
-  bl uart_send
-  movs r5, 8 // eight nibbles in a word
-0:
-  movs r0, 28 // rotate left 4
-  rors r4, r0
-  movs r0, 0xF // lowest nibble mask
-  ands r0, r4
-  cmp r0, 0x9 // number or letter?
-  bhi 1f
-  adds r0, '0
-  b 2f
-1:
-  adds r0, ('A - 0xA)
-2:
-  bl uart_send
-  subs r5, 1
-  bne 0b
-  movs r0, '\r
-  bl uart_send
-  movs r0, '\n
-  bl uart_send
-  pop {pc}
+uart_send:  LDR     R1, =UART0_BASE         // 0x0000 0x4917
+            MOVS    R3, 0b1 << 5            // 0x0002 0x2320  ; TX FIFO FULL
+1:          LDR     R2, [R1, UARTFR_OFST]   // 0x0004 0x670A
+            TST     R2, R3                  // 0x0006 0x421A
+            BNE     1b                      // 0x0008 0xD1FC
+            STRB    R0, [R1, UARTDR_OFST]   // 0x000A 0x7008
+            BX      LR                      // 0x000C 0x4770
+uart_recv:  LDR     R1, =UART0_BASE         // 0x000E 0x4914
+            MOVS    R3, 0b1 << 4            // 0x0010 0x2310  ; RX FIFO EMPTY
+1:          LDR     R2, [R1, UARTFR_OFST]   // 0x0012 0x670A
+            TST     R2, R3                  // 0x0014 0x421A
+            BNE     1b                      // 0x0016 0xF1FC
+            LDRB    R0, [R1, UARTDR_OFST]   // 0x0018 0x7808
+            BX      LR                      // 0x001A 0x4770
+get_char:   PUSH    {LR}                    // 0x001C 0xB500
+            BL      uart_recv               // 0x001E 0xF7FF
+                                            // 0x0020 0xFFF6
+            CMP     R0, R8                  // 0x0022 0x4540
+            POP     {PC}                    // 0x0024 0xBD00
+send_hex:   PUSH    {LR}                    // 0x0026 0xB500
+            MOVS    R4, R0                  // 0x0028 0x0004
+            MOVS    R0, '0                  // 0x002A 0x2030
+            BL      uart_send               // 0x002C 0xF7FF
+                                            // 0x002E 0xFFE8
+            MOVS    R0, 'x                  // 0x0030 0x2078
+            BL      uart_send               // 0x0032 0xF7FF
+                                            // 0x0034 0xFFE5
+            MOVS    R5, 8                   // 0x0036 0x2508 ; EIGHT NIBBLES IN A WORD
+0:          MOVS    R0, 28                  // 0x0038 0x201C ; ROTATE LEFT 4
+            RORS    R4, R0                  // 0x003A 0x41C4
+            MOVS    R0, 0xF                 // 0x003C 0x200F ; LOWEST NIBBLE MASK
+            ANDS    R0, R4                  // 0x003E 0x4020
+            CMP     R0, 0x9                 // 0x0040 0x0000 ; NUMBER OR LETTER?
+            BHI     1f                      // 0x0042 0xD801
+            ADDS    R0, '0                  // 0x0044 0x3030
+            B       2f                      // 0x0046 0xE000
+1:          ADDS    R0, ('A - 0xA)          // 0x0048 0x3037
+2:          BL      uart_send               // 0x004A 0xF7FF
+                                            // 0x004C 0xFFD9
+            SUBS    R5, 1                   // 0x004E 0x3D01
+            BNE     0b                      // 0x0050 0xD1F9
+            MOVS    R0, '\r                 // 0x0052 0x200D
+            BL      uart_send               // 0x0054 0xF7FF
+                                            // 0x0056 0xFFD4
+            MOVS    R0, '\n                 // 0x0058 0x200A
+            BL      uart_send               // 0x005A 0xF7FF
+                                            // 0x005C 0xFFD1
+            POP     {PC}                    // 0x005E 0xBD00
+                                            // 0x0060 0x4000 ; UART0_BASE
+                                            // 0x0062 0x4003
-- 
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