xref: /openbmc/qemu/hw/nvram/eeprom93xx.c (revision b0e70950)
1 /*
2  * QEMU EEPROM 93xx emulation
3  *
4  * Copyright (c) 2006-2007 Stefan Weil
5  *
6  * This program is free software; you can redistribute it and/or modify
7  * it under the terms of the GNU General Public License as published by
8  * the Free Software Foundation; either version 2 of the License, or
9  * (at your option) any later version.
10  *
11  * This program is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
14  * GNU General Public License for more details.
15  *
16  * You should have received a copy of the GNU General Public License
17  * along with this program; if not, see <http://www.gnu.org/licenses/>.
18  */
19 
20 /* Emulation for serial EEPROMs:
21  * NMC93C06 256-Bit (16 x 16)
22  * NMC93C46 1024-Bit (64 x 16)
23  * NMC93C56 2028 Bit (128 x 16)
24  * NMC93C66 4096 Bit (256 x 16)
25  * Compatible devices include FM93C46 and others.
26  *
27  * Other drivers use these interface functions:
28  * eeprom93xx_new   - add a new EEPROM (with 16, 64 or 256 words)
29  * eeprom93xx_free  - destroy EEPROM
30  * eeprom93xx_read  - read data from the EEPROM
31  * eeprom93xx_write - write data to the EEPROM
32  * eeprom93xx_data  - get EEPROM data array for external manipulation
33  *
34  * Todo list:
35  * - No emulation of EEPROM timings.
36  */
37 
38 #include "qemu/osdep.h"
39 #include "hw/nvram/eeprom93xx.h"
40 #include "migration/qemu-file-types.h"
41 #include "migration/vmstate.h"
42 
43 /* Debug EEPROM emulation. */
44 //~ #define DEBUG_EEPROM
45 
46 #ifdef DEBUG_EEPROM
47 #define logout(fmt, ...) fprintf(stderr, "EEPROM\t%-24s" fmt, __func__, ## __VA_ARGS__)
48 #else
49 #define logout(fmt, ...) ((void)0)
50 #endif
51 
52 #define EEPROM_INSTANCE  0
53 #define OLD_EEPROM_VERSION 20061112
54 #define EEPROM_VERSION (OLD_EEPROM_VERSION + 1)
55 
56 #if 0
57 typedef enum {
58   eeprom_read  = 0x80,   /* read register xx */
59   eeprom_write = 0x40,   /* write register xx */
60   eeprom_erase = 0xc0,   /* erase register xx */
61   eeprom_ewen  = 0x30,   /* erase / write enable */
62   eeprom_ewds  = 0x00,   /* erase / write disable */
63   eeprom_eral  = 0x20,   /* erase all registers */
64   eeprom_wral  = 0x10,   /* write all registers */
65   eeprom_amask = 0x0f,
66   eeprom_imask = 0xf0
67 } eeprom_instruction_t;
68 #endif
69 
70 #ifdef DEBUG_EEPROM
71 static const char *opstring[] = {
72   "extended", "write", "read", "erase"
73 };
74 #endif
75 
76 struct _eeprom_t {
77     uint8_t  tick;
78     uint8_t  address;
79     uint8_t  command;
80     uint8_t  writable;
81 
82     uint8_t eecs;
83     uint8_t eesk;
84     uint8_t eedo;
85 
86     uint8_t  addrbits;
87     uint16_t size;
88     uint16_t data;
89     uint16_t contents[];
90 };
91 
92 /* Code for saving and restoring of EEPROM state. */
93 
94 /* Restore an uint16_t from an uint8_t
95    This is a Big hack, but it is how the old state did it.
96  */
97 
98 static int get_uint16_from_uint8(QEMUFile *f, void *pv, size_t size,
99                                  const VMStateField *field)
100 {
101     uint16_t *v = pv;
102     *v = qemu_get_ubyte(f);
103     return 0;
104 }
105 
106 static int put_unused(QEMUFile *f, void *pv, size_t size,
107                       const VMStateField *field, QJSON *vmdesc)
108 {
109     fprintf(stderr, "uint16_from_uint8 is used only for backwards compatibility.\n");
110     fprintf(stderr, "Never should be used to write a new state.\n");
111     exit(0);
112 
113     return 0;
114 }
115 
116 static const VMStateInfo vmstate_hack_uint16_from_uint8 = {
117     .name = "uint16_from_uint8",
118     .get  = get_uint16_from_uint8,
119     .put  = put_unused,
120 };
121 
122 #define VMSTATE_UINT16_HACK_TEST(_f, _s, _t)                           \
123     VMSTATE_SINGLE_TEST(_f, _s, _t, 0, vmstate_hack_uint16_from_uint8, uint16_t)
124 
125 static bool is_old_eeprom_version(void *opaque, int version_id)
126 {
127     return version_id == OLD_EEPROM_VERSION;
128 }
129 
130 static const VMStateDescription vmstate_eeprom = {
131     .name = "eeprom",
132     .version_id = EEPROM_VERSION,
133     .minimum_version_id = OLD_EEPROM_VERSION,
134     .fields = (VMStateField[]) {
135         VMSTATE_UINT8(tick, eeprom_t),
136         VMSTATE_UINT8(address, eeprom_t),
137         VMSTATE_UINT8(command, eeprom_t),
138         VMSTATE_UINT8(writable, eeprom_t),
139 
140         VMSTATE_UINT8(eecs, eeprom_t),
141         VMSTATE_UINT8(eesk, eeprom_t),
142         VMSTATE_UINT8(eedo, eeprom_t),
143 
144         VMSTATE_UINT8(addrbits, eeprom_t),
145         VMSTATE_UINT16_HACK_TEST(size, eeprom_t, is_old_eeprom_version),
146         VMSTATE_UNUSED_TEST(is_old_eeprom_version, 1),
147         VMSTATE_UINT16_EQUAL_V(size, eeprom_t, EEPROM_VERSION, NULL),
148         VMSTATE_UINT16(data, eeprom_t),
149         VMSTATE_VARRAY_UINT16_UNSAFE(contents, eeprom_t, size, 0,
150                                      vmstate_info_uint16, uint16_t),
151         VMSTATE_END_OF_LIST()
152     }
153 };
154 
155 void eeprom93xx_write(eeprom_t *eeprom, int eecs, int eesk, int eedi)
156 {
157     uint8_t tick = eeprom->tick;
158     uint8_t eedo = eeprom->eedo;
159     uint16_t address = eeprom->address;
160     uint8_t command = eeprom->command;
161 
162     logout("CS=%u SK=%u DI=%u DO=%u, tick = %u\n",
163            eecs, eesk, eedi, eedo, tick);
164 
165     if (!eeprom->eecs && eecs) {
166         /* Start chip select cycle. */
167         logout("Cycle start, waiting for 1st start bit (0)\n");
168         tick = 0;
169         command = 0x0;
170         address = 0x0;
171     } else if (eeprom->eecs && !eecs) {
172         /* End chip select cycle. This triggers write / erase. */
173         if (eeprom->writable) {
174             uint8_t subcommand = address >> (eeprom->addrbits - 2);
175             if (command == 0 && subcommand == 2) {
176                 /* Erase all. */
177                 for (address = 0; address < eeprom->size; address++) {
178                     eeprom->contents[address] = 0xffff;
179                 }
180             } else if (command == 3) {
181                 /* Erase word. */
182                 eeprom->contents[address] = 0xffff;
183             } else if (tick >= 2 + 2 + eeprom->addrbits + 16) {
184                 if (command == 1) {
185                     /* Write word. */
186                     eeprom->contents[address] &= eeprom->data;
187                 } else if (command == 0 && subcommand == 1) {
188                     /* Write all. */
189                     for (address = 0; address < eeprom->size; address++) {
190                         eeprom->contents[address] &= eeprom->data;
191                     }
192                 }
193             }
194         }
195         /* Output DO is tristate, read results in 1. */
196         eedo = 1;
197     } else if (eecs && !eeprom->eesk && eesk) {
198         /* Raising edge of clock shifts data in. */
199         if (tick == 0) {
200             /* Wait for 1st start bit. */
201             if (eedi == 0) {
202                 logout("Got correct 1st start bit, waiting for 2nd start bit (1)\n");
203                 tick++;
204             } else {
205                 logout("wrong 1st start bit (is 1, should be 0)\n");
206                 tick = 2;
207                 //~ assert(!"wrong start bit");
208             }
209         } else if (tick == 1) {
210             /* Wait for 2nd start bit. */
211             if (eedi != 0) {
212                 logout("Got correct 2nd start bit, getting command + address\n");
213                 tick++;
214             } else {
215                 logout("1st start bit is longer than needed\n");
216             }
217         } else if (tick < 2 + 2) {
218             /* Got 2 start bits, transfer 2 opcode bits. */
219             tick++;
220             command <<= 1;
221             if (eedi) {
222                 command += 1;
223             }
224         } else if (tick < 2 + 2 + eeprom->addrbits) {
225             /* Got 2 start bits and 2 opcode bits, transfer all address bits. */
226             tick++;
227             address = ((address << 1) | eedi);
228             if (tick == 2 + 2 + eeprom->addrbits) {
229                 logout("%s command, address = 0x%02x (value 0x%04x)\n",
230                        opstring[command], address, eeprom->contents[address]);
231                 if (command == 2) {
232                     eedo = 0;
233                 }
234                 address = address % eeprom->size;
235                 if (command == 0) {
236                     /* Command code in upper 2 bits of address. */
237                     switch (address >> (eeprom->addrbits - 2)) {
238                     case 0:
239                         logout("write disable command\n");
240                         eeprom->writable = 0;
241                         break;
242                     case 1:
243                         logout("write all command\n");
244                         break;
245                     case 2:
246                         logout("erase all command\n");
247                         break;
248                     case 3:
249                         logout("write enable command\n");
250                         eeprom->writable = 1;
251                         break;
252                     }
253                 } else {
254                     /* Read, write or erase word. */
255                     eeprom->data = eeprom->contents[address];
256                 }
257             }
258         } else if (tick < 2 + 2 + eeprom->addrbits + 16) {
259             /* Transfer 16 data bits. */
260             tick++;
261             if (command == 2) {
262                 /* Read word. */
263                 eedo = ((eeprom->data & 0x8000) != 0);
264             }
265             eeprom->data <<= 1;
266             eeprom->data += eedi;
267         } else {
268             logout("additional unneeded tick, not processed\n");
269         }
270     }
271     /* Save status of EEPROM. */
272     eeprom->tick = tick;
273     eeprom->eecs = eecs;
274     eeprom->eesk = eesk;
275     eeprom->eedo = eedo;
276     eeprom->address = address;
277     eeprom->command = command;
278 }
279 
280 uint16_t eeprom93xx_read(eeprom_t *eeprom)
281 {
282     /* Return status of pin DO (0 or 1). */
283     logout("CS=%u DO=%u\n", eeprom->eecs, eeprom->eedo);
284     return eeprom->eedo;
285 }
286 
287 #if 0
288 void eeprom93xx_reset(eeprom_t *eeprom)
289 {
290     /* prepare eeprom */
291     logout("eeprom = 0x%p\n", eeprom);
292     eeprom->tick = 0;
293     eeprom->command = 0;
294 }
295 #endif
296 
297 eeprom_t *eeprom93xx_new(DeviceState *dev, uint16_t nwords)
298 {
299     /* Add a new EEPROM (with 16, 64 or 256 words). */
300     eeprom_t *eeprom;
301     uint8_t addrbits;
302 
303     switch (nwords) {
304     case 16:
305     case 64:
306         addrbits = 6;
307         break;
308     case 128:
309     case 256:
310         addrbits = 8;
311         break;
312     default:
313         assert(!"Unsupported EEPROM size, fallback to 64 words!");
314         nwords = 64;
315         addrbits = 6;
316     }
317 
318     eeprom = (eeprom_t *)g_malloc0(sizeof(*eeprom) + nwords * 2);
319     eeprom->size = nwords;
320     eeprom->addrbits = addrbits;
321     /* Output DO is tristate, read results in 1. */
322     eeprom->eedo = 1;
323     logout("eeprom = 0x%p, nwords = %u\n", eeprom, nwords);
324     vmstate_register(VMSTATE_IF(dev), 0, &vmstate_eeprom, eeprom);
325     return eeprom;
326 }
327 
328 void eeprom93xx_free(DeviceState *dev, eeprom_t *eeprom)
329 {
330     /* Destroy EEPROM. */
331     logout("eeprom = 0x%p\n", eeprom);
332     vmstate_unregister(VMSTATE_IF(dev), &vmstate_eeprom, eeprom);
333     g_free(eeprom);
334 }
335 
336 uint16_t *eeprom93xx_data(eeprom_t *eeprom)
337 {
338     /* Get EEPROM data array. */
339     return &eeprom->contents[0];
340 }
341 
342 /* eof */
343