comparison src/cs/system/main/gcc/irqfiq.S @ 78:95ef11e76c5b

src/cs/system/main/gcc: asm code pieced from Citrine
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 20 Jul 2018 06:46:56 +0000
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77:6b6675a07b70 78:95ef11e76c5b
1 /*
2 * This module contains the assembly shells for IRQ and FIQ, separated
3 * from the architectured vectors only by some simple unconditional
4 * branch instructions.
5 *
6 * Note that TI's way of handling interrupts sacrifices Nucleus' ability
7 * to nest interrupts and minimize the IRQ-disabled window: if my (Falcon's)
8 * understanding is correct, TI's code leaves all further IRQs disabled
9 * for the full execution duration of an IRQ handler. (IRQ handlers are
10 * really LISRs, but TI's GSM fw does not use Nucleus' LISR framework.)
11 */
12
13 .text
14 .code 32
15
16 .globl _INT_IRQ
17 _INT_IRQ:
18 STMDB sp!,{r0-r4} @ used to be a1-a4
19
20 /*
21 * Thanks to TI for discovering and documenting this apparent ARM7TDMI bug:
22
23 BUG correction 1st part -------------------
24 It looks like there is an issue with ARM7 IRQ masking in the CPSR register
25 which leads to crashes in Nucleus+ scheduler.
26 Basically the code below (correct as LOCKOUT = 0xC0) is used in many places by N+ but do not
27 prevent from having an interrupt after the execution of the third line (I mean execution, not
28 fetch).
29 MRS a1,CPSR ; Pickup current CPSR
30 ORR a1,a1,#LOCKOUT ; Build interrupt lockout value
31 MSR CPSR,a1 ; Lockout interrupts
32 * IRQ INTERRUPT ! *
33 Next instructions...
34
35 SW workaround:
36 When a task is interrupted at this point an interrupted context is stored on its task and will
37 be resumed later on at the next instruction but to make a long story short it leads to some
38 problem as the OS does not expect to be interrupted there.
39 Further testing tends to show that the CPSR *seems* to be loaded with the proper masking value
40 but that the IRQ is still triggered (has been hardwarewise requested during the instruction
41 exectution by the ARM7 core?)
42 */
43
44 MRS a1,spsr @ check for the IRQ bug:
45 TST a1,#0x80 @ if the I - flag is set,
46 BNE IRQBUG @ then postpone execution of this IRQ
47 /* Bug correction 1st part end --------------- */
48
49 SUB r4,lr,#4 @ Save IRQ's lr (return address)
50 BL TCT_Interrupt_Context_Save @ Call context save routine
51
52 BL IQ_IRQ_isr @ Call int. service routine
53
54 /* IRQ interrupt processing is complete. Restore context- Never
55 returns! */
56 B TCT_Interrupt_Context_Restore
57
58 /* BUG correction 2nd part ------------------ */
59 IRQBUG: LDMFD sp!,{r0-r4} @ return from interrupt
60 SUBS pc,r14,#4
61 /* BUG correction 2nd part end -------------- */
62
63 .globl _INT_FIQ
64 _INT_FIQ:
65 STMDB sp!,{r0-r4} @ used to be a1-a4
66 SUB r4,lr,#4 @ Save FIQ's lr (return address)
67 BL TCT_Interrupt_Context_Save @ Call context save routine
68
69 BL IQ_FIQ_isr @ Call the FIQ ISR
70
71 /* FIQ interrupt processing is complete. Restore context- Never
72 returns! */
73 B TCT_Interrupt_Context_Restore