FreeCalypso > hg > fc-tourmaline
annotate src/gpf/osl/os_sem_ir.c @ 220:0ed36de51973
ABB semaphore protection overhaul
The ABB semaphone protection logic that came with TCS211 from TI
was broken in several ways:
* Some semaphore-protected functions were called from Application_Initialize()
context. NU_Obtain_Semaphore() called with NU_SUSPEND fails with
NU_INVALID_SUSPEND in this context, but the return value wasn't checked,
and NU_Release_Semaphore() would be called unconditionally at the end.
The latter call would increment the semaphore count past 1, making the
semaphore no longer binary and thus no longer effective for resource
protection. The fix is to check the return value from NU_Obtain_Semaphore()
and skip the NU_Release_Semaphore() call if the semaphore wasn't properly
obtained.
* Some SPI hardware manipulation was being done before entering the semaphore-
protected critical section. The fix is to reorder the code: first obtain
the semaphore, then do everything else.
* In the corner case of L1/DSP recovery, l1_abb_power_on() would call some
non-semaphore-protected ABB & SPI init functions. The fix is to skip those
calls in the case of recovery.
* A few additional corner cases existed, all of which are fixed by making
ABB semaphore protection 100% consistent for all ABB functions and code paths.
There is still one remaining problem of priority inversion: suppose a low-
priority task calls an ABB function, and some medium-priority task just happens
to preempt right in the middle of that semaphore-protected ABB operation. Then
the high-priority SPI task is locked out for a non-deterministic time until
that medium-priority task finishes its work and goes back to sleep. This
priority inversion problem remains outstanding for now.
author | Mychaela Falconia <falcon@freecalypso.org> |
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date | Mon, 26 Apr 2021 20:55:25 +0000 |
parents | 4e78acac3d88 |
children |
rev | line source |
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0
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1 /* |
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2 * This C module is a reconstruction based on the disassembly of |
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3 * os_sem.obj in frame_na7_db_ir.lib from the Leonardo package. |
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4 */ |
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5 |
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6 /* set of included headers from COFF symtab: */ |
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7 #include <stdio.h> |
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8 #include <string.h> |
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9 #include "nucleus.h" |
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10 #include "typedefs.h" |
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11 #include "os.h" |
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12 #include "gdi.h" |
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13 #include "os_types.h" |
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14 #include "os_glob.h" |
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15 |
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16 extern T_OS_SEM_TABLE_ENTRY SemTable[]; |
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17 extern unsigned os_time_to_tick_multiplier; |
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18 |
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19 int |
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20 ReleaseSemaphoreCB(NU_SEMAPHORE *SemCB) |
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21 { |
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22 if (NU_Release_Semaphore(SemCB) == NU_SUCCESS) |
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23 return(OS_OK); |
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24 else |
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25 return(OS_ERROR); |
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26 } |
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27 |
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28 GLOBAL LONG |
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29 os_ReleaseSemaphore(OS_HANDLE TaskHandle, OS_HANDLE SemHandle) |
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30 { |
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31 if (NU_Release_Semaphore(&SemTable[SemHandle].SemCB) == NU_SUCCESS) |
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32 return(OS_OK); |
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33 else |
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34 return(OS_ERROR); |
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35 } |
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36 |
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37 int |
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38 ObtainSemaphoreCB(NU_SEMAPHORE *SemCB, ULONG Timeout, USHORT wait_check) |
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39 { |
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40 UNSIGNED nu_timeout; |
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41 STATUS sts; |
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42 int ret; |
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43 |
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44 ret = OS_OK; |
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45 if (Timeout != OS_SUSPEND) |
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46 nu_timeout = TIME_TO_SYSTEM_TICKS(Timeout); |
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47 else if (wait_check == 1) |
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48 nu_timeout = 1; |
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49 else |
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50 nu_timeout = NU_SUSPEND; |
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51 for (;;) { |
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52 sts = NU_Obtain_Semaphore(SemCB, nu_timeout); |
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53 switch (sts) { |
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54 case NU_SUCCESS: |
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55 return(ret); |
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56 case NU_INVALID_SEMAPHORE: |
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57 return(OS_ERROR); |
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58 case NU_INVALID_SUSPEND: |
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59 nu_timeout = 0; |
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60 continue; |
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61 case NU_TIMEOUT: |
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62 case NU_UNAVAILABLE: |
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63 if (nu_timeout == 1 && wait_check == 1) { |
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64 nu_timeout = NU_SUSPEND; |
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65 ret = OS_WAITED; |
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66 continue; |
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67 } |
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68 return(OS_TIMEOUT); |
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69 default: |
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70 /* |
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71 * Disassembly reveals that the original code |
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72 * has an endless loop here, the equivalent |
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73 * of continue. My guess is that they simply |
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74 * forgot the default case, and so control |
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75 * falls onto the closing brace of the switch |
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76 * and then onto the closing brace of the for |
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77 * loop. But I prefer better error handling, |
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78 * hence the present addition. - Space Falcon |
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79 */ |
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80 return(OS_ERROR); |
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81 } |
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82 } |
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83 } |
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84 |
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85 GLOBAL LONG |
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86 os_ObtainSemaphore(OS_HANDLE TaskHandle, OS_HANDLE SemHandle, ULONG Timeout) |
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87 { |
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88 if (SemHandle > MaxSemaphores) |
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89 return(OS_ERROR); |
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90 return ObtainSemaphoreCB(&SemTable[SemHandle].SemCB, Timeout, 0); |
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91 } |