Mon, 14 Jan 2013 09:22:12 +0000
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 _WD279X_H
2 #define _WD279X_H
4 #include <stdbool.h>
5 #include <stddef.h>
6 #include <stdint.h>
7 #include <stdio.h>
9 /// WD279x registers
10 typedef enum {
11 WD2797_REG_STATUS = 0, ///< Status register
12 WD2797_REG_COMMAND = 0, ///< Command register
13 WD2797_REG_TRACK = 1, ///< Track register
14 WD2797_REG_SECTOR = 2, ///< Sector register
15 WD2797_REG_DATA = 3 ///< Data register
16 } WD2797_REG;
18 /// WD279x emulator error codes
19 typedef enum {
20 WD2797_ERR_OK = 0, ///< Operation succeeded
21 WD2797_ERR_BAD_GEOM = -1, ///< Bad geometry, or image file too small
22 WD2797_ERR_NO_MEMORY = -2 ///< Out of memory
23 } WD2797_ERR;
25 typedef struct {
26 // Current track, head and sector
27 int track, head, sector;
28 // Track and sector registers
29 int track_reg, sector_reg;
30 // Geometry of current disc
31 int geom_secsz, geom_spt, geom_heads, geom_tracks;
32 // IRQ status
33 bool irq;
34 // Status of last command
35 uint8_t status;
36 // Last command uses DRQ bit?
37 bool cmd_has_drq;
38 // The last value written to the data register
39 uint8_t data_reg;
40 // Last step direction. -1 for "towards zero", 1 for "away from zero"
41 int last_step_dir;
42 // Data buffer, current DRQ pointer and length
43 uint8_t *data;
44 size_t data_pos, data_len;
45 // Current disc image file
46 FILE *disc_image;
47 // Write protect flag
48 int writeable;
49 // LBA at which to start writing
50 int write_pos;
51 // True if a format command is in progress
52 int formatting;
53 } WD2797_CTX;
55 /**
56 * @brief Initialise a WD2797 context.
57 * @param ctx WD2797 context.
58 *
59 * This must be run once when the context is created.
60 */
61 void wd2797_init(WD2797_CTX *ctx);
63 /**
64 * @brief Reset a WD2797 context.
65 * @param ctx WD2797 context.
66 *
67 * This should be run if the WD2797 needs to be reset (nRST line toggled).
68 */
69 void wd2797_reset(WD2797_CTX *ctx);
71 /**
72 * Deinitialise a WD2797 context.
73 * @param ctx WD2797 context.
74 */
75 void wd2797_done(WD2797_CTX *ctx);
77 /**
78 * @brief Read IRQ Rising Edge status. Clears Rising Edge status if it is set.
79 * @note No more IRQs will be sent until the Status Register is read, or a new command is written to the CR.
80 * @param ctx WD2797 context.
81 */
82 bool wd2797_get_irq(WD2797_CTX *ctx);
84 /**
85 * @brief Read DRQ status.
86 * @param ctx WD2797 context.
87 */
88 bool wd2797_get_drq(WD2797_CTX *ctx);
90 /**
91 * @brief Assign a disc image to the WD2797.
92 * @param ctx WD2797 context.
93 * @param fp Disc image file, already opened in "r+b" mode.
94 * @param secsz Sector size: either 128, 256, 512 or 1024.
95 * @param spt Sectors per track.
96 * @param heads Number of heads (1 or 2).
97 * @return Error code; WD279X_E_OK if everything worked OK.
98 */
99 WD2797_ERR wd2797_load(WD2797_CTX *ctx, FILE *fp, int secsz, int spt, int heads, int writeable);
101 /**
102 * @brief Deassign the current image file.
103 * @param ctx WD2797 context.
104 */
105 void wd2797_unload(WD2797_CTX *ctx);
107 /**
108 * @brief Read WD279x register.
109 * @param ctx WD2797 context
110 * @param addr Register address (0, 1, 2 or 3)
111 */
112 uint8_t wd2797_read_reg(WD2797_CTX *ctx, uint8_t addr);
114 /**
115 * @brief Write WD279X register
116 * @param ctx WD2797 context
117 * @param addr Register address (0, 1, 2 or 3)
118 * @param val Value to write
119 */
120 void wd2797_write_reg(WD2797_CTX *ctx, uint8_t addr, uint8_t val);
122 void wd2797_dma_miss(WD2797_CTX *ctx);
123 #endif