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Comprehensive technical documentation covering: - Hardware: OCS/ECS/AGA custom chip registers, Copper & Blitter deep dives - Boot sequence: cold boot through startup-sequence - Binary format: HUNK executable spec, relocation, debug info - Linking & ABI: .fd files, LVO tables, register calling conventions - Exec kernel: tasks, interrupts, memory, signals, semaphores - AmigaDOS: file I/O, FFS/OFS layout, CLI/Shell scripting - Graphics: planar bitmaps, Copper programming, HAM/EHB modes - Intuition: screens, windows, IDCMP, BOOPSI - Devices: trackdisk, SCSI, serial, timer, audio, keyboard - Libraries: utility, expansion, IFFParse, locale, ARexx - Networking: bsdsocket API, SANA-II, TCP/IP stack comparison - Toolchain: GCC, vasm/vlink, SAS/C, NDK, debugging - Reverse engineering: IDA/Ghidra setup, compiler fingerprints, case studies - CPU & MMU: 68040/060 emulation libs, PMMU, cache management - Driver development: SANA-II, Picasso96/RTG, AHI audio All files include breadcrumb navigation. No local paths or proprietary content.
118 lines
3.2 KiB
Markdown
118 lines
3.2 KiB
Markdown
[← Home](../../README.md) · [Reverse Engineering](../README.md)
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# Serial Debugging — kprintf and Serial Output
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## Overview
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The Amiga's built-in serial port is the primary low-level debugging channel. `kprintf()` (kernel printf) and `RawPutChar()` write directly to the serial hardware, bypassing `dos.library` and working even from interrupt context or before OS initialization.
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---
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## `kprintf()` — Kernel Printf
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`kprintf()` is a ROM debug function present in Kickstart 1.3 and later debug ROMs. It formats a string and outputs each character via `RawPutChar`.
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```c
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/* Prototype (exec internal, not in NDK — declare manually): */
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void kprintf(const char *fmt, ...);
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/* Arguments in: D1=fmt, stack args (unlike standard AmigaOS register ABI) */
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```
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### Calling `kprintf` from Assembly
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```asm
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MOVEA.L 4.W, A6 ; SysBase
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LEA _fmt_str(PC), A0 ; format string
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MOVE.L A0, -(SP) ; push as stack argument
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MOVE.L A0, D1 ; some implementations use D1
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JSR (-$F0,A6) ; RawDoFmt or debug rom entry
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; OR for ROM debug builds:
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JSR _kprintf
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```
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> [!NOTE]
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> `kprintf` is **not available** in standard Kickstart 3.1 release ROMs. Use `debug.lib` stubs (`dprintf`) or `RawDoFmt + RawPutChar` instead.
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---
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## `RawDoFmt` + `RawPutChar` — Universal Approach
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This works on **all** Kickstart versions (1.2+):
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```c
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/* Format into a buffer and output via RawPutChar */
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static void serial_putchar(UBYTE c, APTR dummy) {
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/* write directly to serial data register */
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volatile UWORD *SERDATR = (UWORD *)0xDFF018;
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volatile UWORD *SERDATW = (UWORD *)0xDFF030;
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volatile UWORD *SERDATSTAT;
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/* Wait for TBE (transmit buffer empty) */
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while (!(*SERDATR & 0x2000));
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*SERDATW = 0x0100 | c; /* 8 bits + start bit */
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}
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void dbg_printf(const char *fmt, ...) {
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UBYTE buf[256];
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va_list args;
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va_start(args, fmt);
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/* RawDoFmt(fmt, args, putChar, buf) */
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RawDoFmt((STRPTR)fmt, &args,
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(VOID (*)())serial_putchar, buf);
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va_end(args);
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}
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```
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Or simpler — write to the serial hardware directly:
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```c
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static void SerPutChar(UBYTE c) {
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while (!(*((volatile UWORD *)0xDFF018) & 0x2000)); /* wait TBE */
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*((volatile UWORD *)0xDFF030) = 0x0100 | c;
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}
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```
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---
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## `debug.lib` (SAS/C)
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SAS/C ships `debug.lib` providing `dprintf`:
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```c
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#include <debug.h>
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dprintf("mylib: Open called, name=%s\n", name);
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```
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Output goes to the serial port at the rate set by SERPER (default 9600 baud on startup, 115200 if set).
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---
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## Setting Baud Rate
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```c
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/* Set serial to 115200 baud (PAL, 3.546895 MHz clock): */
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/* SERPER = (clock / (16 * baud)) - 1 */
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/* = (3546895 / (16 * 115200)) - 1 = 0 */
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volatile UWORD *SERPER = (UWORD *)0xDFF032;
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*SERPER = 0x0000; /* 115200 on PAL */
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```
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---
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## Host-Side Capture
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```bash
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# macOS (USB-serial adapter):
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screen /dev/cu.usbserial-XXXX 115200
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# or:
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stty -f /dev/cu.usbserial-XXXX 115200 raw && cat /dev/cu.usbserial-XXXX
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```
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MiSTer FPGA: the UART bridge is exposed on the MiSTer IO board or via the DE10-Nano UART.
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---
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## References
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- NDK39: `exec/execbase.h` — `RawDoFmt`, `RawPutChar` LVOs
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- `01_hardware/ocs_a500/paula_serial.md` — SERPER, SERDATR, SERDATW register details
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- Aminet: `debug/misc/dprintf.lha`
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