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ARM7 BIOS: Difference between revisions

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m →SVC list: flagged HaltMaybe for checking, since it looks like the idle thread in ARM7 OS calls this in place of the CP15 stuff in ARM9. haven't looked very deep yet though
 
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== BIOS and Bootrom ==
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The ARM7 BIOS is split into two parts:
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# the actual BIOS which is 0x8000 bytes long and starts at 0x0
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# the bootrom which is probably also 0x8000 bytes long and starts at 0x8000
 
*The contents of 1) can only be read by instructions within the BIOS. It can therefore be dumped by applying some IRQ timer trick to find a usable ''ldr'' instruction or by just using the memcpy at 0x6bb0 with the usual arguments.
*The contents of 2) can only be read until bit 0 in register '''0x04004000 or 0x04004001 (?)''' is cleared. It is disabled after it has been executed and can never be read again until the device is reset.
 
== SVC list ==
The BIOS provides the following SVC functions. Every SVC not mentioned here just jumps to an infinite loop at 0x16c (b .)
 
Caution: In below table, "n/a" in the NAME column seems to mean "not altered" (ie. same as in NDS BIOS). Whilst "n/a" in the DESCRIPTION column seems to mean "not any" (ie. nobody has written a description yet).
 
{| class="wikitable sortable" width="55%"
|-
! SVC
! NAME
! DESCRIPTION
|-
|01
|n/a
|n/a
|-
|02
|n/a
|n/a
|- 
|03
|WaitByLoop
|n/a
|-
|04
|IntrWait
|n/a
|-
|05
|VSyncWait
|n/a
|-
|06
|HaltMaybe{{check}}
|n/a
|-
|07
|StopMaybe
|n/a
|-
|08
|n/a
|n/a
|-
|09
|n/a
|n/a
|-
|0b
|CPUSet
|n/a
|-
|0c
|CpuFastSet
|n/a
|-
|0d
|n/a
|n/a
|-
|0e
|CRC16
|n/a
|-
|10
|n/a
|n/a
|-
|11
|n/a
|n/a
|-
|12
|n/a
|n/a
|-
|13
|n/a
|n/a
|-
|14
|n/a
|n/a
|-
|15
|n/a
|n/a
|-
|19
|n/a
|n/a
|-
|1a
|GetSinTable
|n/a
|-
|1b
|GetPitchTable
|n/a
|-
|1c
|GetVolumeTable
|n/a
|-
|1d
|n/a
|n/a
|-
|1f
|CustomHalt
|n/a
|-
|20
|n/a
|n/a
|-
|21
|n/a
|n/a
|-
|22
|n/a
|n/a
|-
|23
|n/a
|n/a
|-
|24
|SHA1_init
|n/a
|-
|25
|SHA1_update
|n/a
|-
|26
|SHA1_finalize
|n/a
|-
|27
|SHA1
|n/a
|-
|28
|SHA1_compare
|n/a
|-
|29
|SHA1_random_maybe
|n/a
|}
 
== reset vectors et al ==
 
The first few words of the BIOS cannot be dumped. You can deduce them by tracing the code though (all values are noted in big endian here):
  ea000006
ea000006
ea00001f
ea000004
ea000003
eafffffe
ea000013
ea000000
 
== See Also ==
 
* [[ARM9 SWI Functions]]
* [[Bootloader]] (Stage 1 contained in BIOS ROMs)
Retrieved from "https://dsibrew.org/wiki/ARM7_BIOS"