vhaudiquet
2dceb2c8a4
The diagnostic wrapper phase (magenta fill, 3-blink train, 5 s hold) is removed; the shim keeps only the load-bearing display revival (OVL_EN, OVL0_2L_EN, backlight GPIOs) and the patched branch to U-Boot. U-BOOT.md documents the boot chain, payload layout constants, build/flash/verify commands, recovery and the U-Boot tree state. U-Boot was rebuilt with the user's hand-tuned .config (16x32 font, CONFIG_CHROMEOS) without re-running the defconfig.
47 lines
1.6 KiB
ArmAsm
47 lines
1.6 KiB
ArmAsm
/*
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* krane payload entry shim — runs at 0x40000040 right after the
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* depthcharge handoff (MMU off, caches off; position-independent:
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* immediate-encoded addresses only).
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*
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* depthcharge's display_cleanup() stops the overlay engines and drops
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* the backlight before jumping to the payload; this shim undoes those
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* writes so the screen stays alive until U-Boot's scanout driver
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* probes (the driver repeats the revival itself). The shim cannot be
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* removed: depthcharge jumps to payload+0x40, while U-Boot's PIE
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* fixup needs its runtime _start 4K-aligned — so U-Boot sits at image
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* offset 0x1000 and this shim branches there (branch imm26 patched at
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* build time by build-uboot-payload.sh).
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*
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* Register sources (all verified on device, RESEARCH.md rounds 4/10):
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* OVL0 base 0x14008000: OVL_EN @ +0x000c, OVL0_2L_EN @ +0x100c
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* (device-era depthcharge mtk_ddp.c offsets).
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* GPIO controller 0x10005000, dout block +0x100, 16 B per 32-pin
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* group, set @ +4 (mt8183.h GpioRegs):
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* DISP_PWM = pin 43 (bit 11, set 0x10005114),
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* EN_LCD_BL = pin 176 (bit 16, set 0x10005154).
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*/
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.text
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.globl _start
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_start:
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/* OVL_EN = 1 */
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mov w2, #1
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mov w3, #0x800c
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movk w3, #0x1400, lsl #16
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str w2, [x3]
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/* OVL0_2L_EN = 1 */
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mov w3, #0x900c
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movk w3, #0x1400, lsl #16
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str w2, [x3]
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/* backlight on: pin 43 (DISP_PWM), dout set 0x10005114, bit 11 */
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mov w2, #0x800
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mov w3, #0x5114
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movk w3, #0x1000, lsl #16
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str w2, [x3]
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/* backlight on: pin 176 (EN_LCD_BL), dout set 0x10005154, bit 16 */
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mov w2, #0x10000
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mov w3, #0x5154
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movk w3, #0x1000, lsl #16
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str w2, [x3]
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1: b . /* PATCHED: branch to U-Boot entry */
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