Cache Control Register Bits: Difference between revisions

Revision as of 04:48, 23 October 2026 RemmyLee (Main page: drop the Hardware Tests lede)	Revision as of 05:11, 23 October 2026 RemmyLee (Hardware tests: 72 more test pages, listed on the main page by area; RUN.toml no longer published)
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	+	---
	+	title: Cache Control Register Bits
	+	type: test
	+	summary: Measures the effect of BCC bits 11 to 17 on bus, cache and DMA timing, and what narrow reads of BCC return.
	+	category: Hardware tests
	+	info: Machine = SCPH-5501
	+	info: Program = bcc-bits and bcc-narrow (pcsx-redux nugget)
	+	---
	+
	+	## Overview
	+
	+	The cache control register BCC sits at FFFE0130h, and the BIOS leaves it at 0001E988h. psx-spx names bits 12 to 17 INTP, RDPRI, NOPAD, BGNT, LDSCH and NOSTR after the LR33300 manual.[^srcb]
	+
	+	The bcc-bits program flips one bit at a time away from 0001E988h and times a fixed set of sequences against the unchanged value. Interrupts are masked, and root counter 2 counts system clock cycles. The sequences are a RAM load and its use, a RAM store, a store then a load, a RAM load and a NOP, a scratchpad access, an I/O access, uncached instruction fetch, and a DMA transfer running against the CPU. Each figure is the smallest of 8 runs, and each row is taken twice. The program prints UNSTABLE when the two passes differ, and MOVED when the row differs from the unchanged value. As a control it also clears bit 11, which turns the instruction cache off.[^srcb]
	+
	+	The bcc-narrow program reads BCC three times with LW, with LB at each byte offset and with LH at each halfword offset.[^runn]
	+
	+	## Results
	+
	+	### BCC Bits
	+
	+	Bits 12 (INTP), 13 (RDPRI) and 14 (NOPAD) changed no sequence by more than 3 counts, and neither did the unchanged value between its own two passes. The DMA row varied by a few counts in every row, so most rows are marked UNSTABLE.[^runb]
	+
	+	Table: Counts with one BCC bit changed
	+
	+	\| Value \| Bit \| RAM load and NOP \| Uncached fetch \| DMA against the CPU \|
	+	\| --- \| --- \| --- \| --- \| --- \|
	+	\| 0001E988h \| none \| 292 \| 590 \| 4647 to 4651 \|
	+	\| 0001F988h \| INTP \| 292 \| 592 \| 4650 \|
	+	\| 0001C988h \| RDPRI \| 292 \| 590 \| 4650 \|
	+	\| 0001A988h \| NOPAD \| 292 \| 591 \| 4650 to 4653 \|
	+	\| 00016988h \| BGNT \| 292 \| 591 \| never finished \|
	+	\| 0000E988h \| LDSCH \| 357 \| 591 \| 4652 to 4653 \|
	+	\| 0003E988h \| NOSTR \| 292 \| 624 \| 4646 to 4651 \|
	+	\| 0001E188h \| bit 11 cleared \| 1114 \| 590 \| 5110 to 5111 \|
	+
	+	Clearing BGNT (bit 15) stopped the DMA transfer from finishing: the channel was still busy when the program gave up, and it drained once BCC was restored. Clearing LDSCH (bit 16) slowed a RAM load followed by a NOP from 292 to 357 counts and added 1 or 2 counts to the other sequences. Setting NOSTR (bit 17) slowed uncached instruction fetch from 590 to 624 counts.[^runb]
	+
	+	Clearing bit 11 made every cached sequence run at the uncached speed: the RAM load and its use took 590 counts against 262, and the scratchpad sequence 592 against 100.[^runb]
	+
	+	### Narrow Reads of BCC
	+
	+	A word read of BCC returns 0001E988h. A byte read at offset 0 returns 88h, and byte reads at offsets 1, 2 and 3 return 00h. A halfword read at offset 0 returns E988h and at offset 2 returns 0000h. All three passes read the same values.[^runn]
	+
	+	## Runs
	+
	+	### 22 October 2026 (link-2)
	+
	+	[BCCBITS.txt](/tests/raw/20261022T2232Z-5501a-link-2/bccbits/BCCBITS.txt):
	+
	+	```
	+	BCCBITS-START bcc=0001e988
	+	BCC base set=0001e988 read=0001e988 ramLoadUse=262 ramStore=69 storeLoad=422 ramLoadNop=292 spad=100 mmio=163 ifetchUnc=590 dmaContend=262 dmaDone=4647/4650 UNSTABLE BASE
	+	BCC INTP set=0001f988 read=0001f988 ramLoadUse=262 ramStore=69 storeLoad=422 ramLoadNop=292 spad=100 mmio=163 ifetchUnc=592 dmaContend=262 dmaDone=4650/4650 UNSTABLE MOVED
	+	BCC RDPRI set=0001c988 read=0001c988 ramLoadUse=262 ramStore=69 storeLoad=422 ramLoadNop=292 spad=100 mmio=163 ifetchUnc=590 dmaContend=262 dmaDone=4650/4650 same
	+	BCC NOPAD set=0001a988 read=0001a988 ramLoadUse=262 ramStore=70 storeLoad=422 ramLoadNop=292 spad=100 mmio=163 ifetchUnc=591 dmaContend=262 dmaDone=4650/4653 UNSTABLE MOVED
	+	BCC BGNT set=00016988 read=00016988 ramLoadUse=262 ramStore=69 storeLoad=422 ramLoadNop=292 spad=100 mmio=163 ifetchUnc=591 dmaContend=262 dmaDone=65535/65535 dmaLeftBusy drainedAfterRestore UNSTABLE MOVED
	+	BCC LDSCH set=0000e988 read=0000e988 ramLoadUse=263 ramStore=70 storeLoad=424 ramLoadNop=357 spad=101 mmio=165 ifetchUnc=591 dmaContend=263 dmaDone=4653/4652 UNSTABLE MOVED
	+	BCC NOSTR set=0003e988 read=0003e988 ramLoadUse=262 ramStore=69 storeLoad=422 ramLoadNop=292 spad=100 mmio=163 ifetchUnc=624 dmaContend=262 dmaDone=4651/4646 UNSTABLE MOVED
	+	BCC ctl-IS1 set=0001e188 read=0001e188 ramLoadUse=590 ramStore=317 storeLoad=727 ramLoadNop=1114 spad=592 mmio=296 ifetchUnc=590 dmaContend=590 dmaDone=5110/5111 UNSTABLE MOVED
	+	BCC base set=0001e988 read=0001e988 ramLoadUse=262 ramStore=69 storeLoad=422 ramLoadNop=292 spad=100 mmio=163 ifetchUnc=590 dmaContend=262 dmaDone=4651/4651 UNSTABLE same
	+	BCCBITS-DONE
	+	ResetGraph:jtb=801e78b8,env=801e7900
	+	```
	+
	+	[bench.txt](/tests/raw/20261022T2232Z-5501a-link-2/bccbits/bench.txt):
	+
	+	```
	+	1668 bytes of TTY text in psx.log
	+	```
	+
	+	[when.txt](/tests/raw/20261022T2232Z-5501a-link-2/bccbits/when.txt):
	+
	+	```
	+	20261022T2232Z
	+	```
	+
	+	### 22 October 2026 (link-3)
	+
	+	[BCCNARROW.txt](/tests/raw/20261022T2232Z-5501a-link-3/bccnarrow/BCCNARROW.txt):
	+
	+	```
	+	BCCN-START
	+	BCCN rep=0 lw +0 0001e988
	+	BCCN rep=0 BEFORE lb +0
	+	BCCN rep=0 lb +0 88
	+	BCCN rep=0 BEFORE lb +1
	+	BCCN rep=0 lb +1 00
	+	BCCN rep=0 BEFORE lb +2
	+	BCCN rep=0 lb +2 00
	+	BCCN rep=0 BEFORE lb +3
	+	BCCN rep=0 lb +3 00
	+	BCCN rep=0 BEFORE lh +0
	+	BCCN rep=0 lh +0 e988
	+	BCCN rep=0 BEFORE lh +2
	+	BCCN rep=0 lh +2 0000
	+	BCCN rep=1 lw +0 0001e988
	+	BCCN rep=1 BEFORE lb +0
	+	BCCN rep=1 lb +0 88
	+	BCCN rep=1 BEFORE lb +1
	+	BCCN rep=1 lb +1 00
	+	BCCN rep=1 BEFORE lb +2
	+	BCCN rep=1 lb +2 00
	+	BCCN rep=1 BEFORE lb +3
	+	BCCN rep=1 lb +3 00
	+	BCCN rep=1 BEFORE lh +0
	+	BCCN rep=1 lh +0 e988
	+	BCCN rep=1 BEFORE lh +2
	+	BCCN rep=1 lh +2 0000
	+	BCCN rep=2 lw +0 0001e988
	+	BCCN rep=2 BEFORE lb +0
	+	BCCN rep=2 lb +0 88
	+	BCCN rep=2 BEFORE lb +1
	+	BCCN rep=2 lb +1 00
	+	BCCN rep=2 BEFORE lb +2
	+	BCCN rep=2 lb +2 00
	+	BCCN rep=2 BEFORE lb +3
	+	BCCN rep=2 lb +3 00
	+	BCCN rep=2 BEFORE lh +0
	+	BCCN rep=2 lh +0 e988
	+	BCCN rep=2 BEFORE lh +2
	+	BCCN rep=2 lh +2 0000
	+	BCCN-DONE
	+	ResetGraph:jtb=801e78b8,env=801e7900
	+	```
	+
	+	[bench.txt](/tests/raw/20261022T2232Z-5501a-link-3/bccnarrow/bench.txt):
	+
	+	```
	+	940 bytes of TTY text in psx.log
	+	```
	+
	+	Output files that match an earlier run: [when.txt](/tests/raw/20261022T2232Z-5501a-link-3/bccnarrow/when.txt) (as run 20261022T2232Z-5501a-link-2).
	+
	+	## References
	+
	+	[^srcb]: pcsx-redux nugget, tests/bcc-bits/bcc-bits.c, header comment and the ctl-IS1 control row. MIT License. https://github.com/pcsx-redux/nugget
	+	[^runb]: Hardware test run 20261022T2232Z-5501a-link-2 on the SCPH-5501: [BCCBITS.txt](/tests/raw/20261022T2232Z-5501a-link-2/bccbits/BCCBITS.txt).
	+	[^runn]: Hardware test run 20261022T2232Z-5501a-link-3 on the SCPH-5501: [BCCNARROW.txt](/tests/raw/20261022T2232Z-5501a-link-3/bccnarrow/BCCNARROW.txt).

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