Mon, 14 Jan 2013 09:22:12 +0000

Philip Pemberton <>
Mon, 14 Jan 2013 09:22:12 +0000
changeset 118
parent 91

More bus error fixes for FreeBee

I have fixed two more bus error handling bugs in FreeBee. First, the CPU core was executing the instruction regardless of whether a bus error occurs when fetching the opcode (which caused it to execute a bogus instruction in such cases). The other one was related to one of my previous fixes - the jump to the bus error vector was at the beginning of the main loop, so it wouldn't be called immediately after the bus error occurred if the timeslot expired, causing the return address to be off.

With these fixes, Unix now runs enough to get into userspace and run the install script (it is also possible to break out and get a shell prompt). However, many commands segfault semi-randomly (or more specifically, it seems that some child processes forked by the shell might be segfaulting before they can exec the command program), so installing the system isn't possible yet. I am not sure exactly what the bug is, but it seems to be related to some function in the shell returning null when the code calling it is assuming that it won't. What the function is, or why it is returning null, I'm not sure (the shell is built without the shared libc and is stripped, making identifying the function harder). I suspect that the function might be in libc, but that is hard to tell.

Author: Andrew Warkentin <andreww591 gmail com>

     1 #ifndef _KEYBOARD_H
     2 #define _KEYBOARD_H
     4 #include "SDL.h"
     6 /// Keyboard buffer size in bytes
     7 #define KEYBOARD_BUFFER_SIZE 256
     9 typedef struct {
    10 	/// Key states
    11 	int keystate[0x80];
    13 	/// Keyboard buffer
    14 	uint8_t buffer[KEYBOARD_BUFFER_SIZE];
    16 	/// Read pointer
    17 	size_t readp;
    19 	/// Write pointer
    20 	size_t writep;
    22 	/// Number of bytes in keyboard buffer
    23 	size_t buflen;
    25 	/// Transmit Interrupt Enable
    26 	bool txie;
    28 	/// Receive Interrupt Enable
    29 	bool rxie;
    31 	/// "Keyboard State Changed" flag
    32 	bool update_flag;
    35 /**
    36  * Initialise a keyboard state block.
    37  *
    38  * Call this once when the keyboard is added to the emulation.
    39  */
    40 void keyboard_init(KEYBOARD_STATE *ks);
    42 /**
    43  * SDL_Event delegation routine.
    44  *
    45  * Call this when an SDL keyup or keydown event is received.
    46  */
    47 void keyboard_event(KEYBOARD_STATE *ks, SDL_Event *ev);
    49 /**
    50  * Keyboard scan routine.
    51  *
    52  * Call this periodically to scan the keyboard. 60 times/sec should be fine.
    53  */
    54 void keyboard_scan(KEYBOARD_STATE *ks);
    56 bool keyboard_get_irq(KEYBOARD_STATE *ks);
    57 uint8_t keyboard_read(KEYBOARD_STATE *ks, uint8_t addr);
    58 void keyboard_write(KEYBOARD_STATE *ks, uint8_t addr, uint8_t val);
    60 #endif