DB: THE TILE AWAKENS
2 | DB: THE TILE AWAKENS | MAY 13, 2024 | CONFIDENTIAL
The Tile Cache Probe
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The Depth Block process all begins with a tile arriving
on the SC_DB_tile interface. The entry point is the tile
cache probe dispatcher.
SC_DB_TILE
The TCP holds an input fifo, usc_db_tile_fifo, which
handles the requirements of the credit debit
interface. This fifo is compiled ram based.
After the first fifo, TCP dispatcher sends the tile
coordinates to the TCP cache manager if necessary.
The cache manager will send hit/miss information to
the next stated, the hi-z-s checker
The tile is deposited, along with whether the cm was
queried, in a reg-based fifo of the same depth at the
first. It waits for the cache manager to respond here
TCP will assert RTS when CM has responded
3 | DB: THE TILE AWAKENS | MAY 13, 2024 | CONFIDENTIAL
Input Fifo
Cache
Manager
s2s3 fifo
HIZ_S_CHECKER
The Hierarchical Z S Checker
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First, tile information is accepted from the TCP and
deposited in the TCP_TILE_FIFO. The tile fifo matches the
depth of the cache lookup time so that cache data,
containing the “dst” is aligned with the “src” data from
TCP. Output of FIFO is the q0 stage
Plane information is converted to 14-bit UNORM this is the
q1 stage
The q1 stage goes to both the “depth test” and “stencil
compare” subblocks
In the depth test, the current dst value is checked against a
register-determined minz and maxz. If the dst is outside
the range, the tile fails DB test and will be culled other, the
Z test is done and a z_result is generated. The output of Z
test is q2
In the stencil compare, the stencil values are evaluated and
an stest_result is generated. The output of S compare is
q2
The z_result and stest_results are brought into
db_his_stencil_test where a final hiz_result is generated.
There is no register stage in this block, so we are still at q2
The final result is flopped to the hz_tk outputs which will
send the information to the tile_kill block
4 | DB: THE TILE AWAKENS | MAY 13, 2024 | CONFIDENTIAL
tcp_hz
TCP_TILE_FIFO
q0
float to U14
q1
DEPTH TEST
(DB and Z)
STENCIL
COMPARE
q2
HIS_TEST
q2
OUTPUT FLOP
hz_tk (q3)
Updating the Tile Cache
HI-Z
5 | DB: THE TILE AWAKENS | MAY 13, 2024 | CONFIDENTIAL
TILE CACHE
TILE SUMMARIZER
Hi Z Test
• Function: >=<
• Does the tile absolutely meet the test criteria?
• Example :
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zfunc is 1 means <
current (dst): min = 0x30, max = 0x3000
new(src): min = 0x20, max = 0x800
Result: MAYPASS, MAYFAIL
• Result of Hi-Z updates the tile cache:
1.
HiZ grows ZNear
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MinZ is set to min(old MinZ, tile MinZ) for any tile that can pass if the Z is < the destination.
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MaxZ is set to max(old MaxZ, tile MaxZ) for any tile that can pass if the Z is > the destination.
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The tile MinZ and MaxZ are treated as the viewport min and viewport max if shader Z export is enabled.
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The HiZ logic does the min and max operations above. The tile cache just writes the values handed to it.
2.
HiZ shrink of Z Far if tile is fully covered
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MaxZ is set to min(old MaxZ, tile MaxZ) for any tile that can pass if the Z is < the destination.
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MinZ is set to max(old MinZ, tile MinZ) for any tile that can pass if the Z is > the destination.
6 | DB: THE TILE AWAKENS | MAY 13, 2024 | CONFIDENTIAL
Hi Stencil Test
Reg
Compare 0
Compare 1
Compare
Val, Func, Enable
SResults
May Pass, May Fail
Back/Front
Face States
Tile
Compare
Mask
Expand Compare State
Compare
Mask
Backfacing
Compare
Val, Func, Enable
SResults
May Pass, May Fail
Stencil State
Expand Compare State
Value, Tile may be <, >, =
Convert to
<=, >=
Value, Tile may be <, >, =
Value,
Tile may be <, >, =
Value, Mask
Tile may be <, >, =
Stencil Test Mask
Stencil Func
Compare Vs Ref?
Final
Stencil
State
Get Known
Known
Expand
Known Mask[7:0]
Known Value[7:0]
Known Mask[7:0]
Known Value[7:0]
Known
Known Merge (OR)
Convert to
<=, >=
Value, Mask
Tile may be <, >, =
Stencil Test Mask
Stencil Func
Known
Tile may be {< > =} Ref
Compare Vs Ref?
Tile may be {< > =} Ref
&
Tile may be {< > =} Ref
Stencil Func
May Pass, May Fail
7 | DB: THE TILE AWAKENS | MAY 13, 2024 | CONFIDENTIAL
Value,
Tile may be <, >, =
Func
Hi Stencil Test
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Unlike Z, an operation can occur on the stencil value even when things value
An operation is specified for STENCIL FAIL, STENCIL PASS/ZPASS, and STENCIL PASS/ZFAIL
There are also FrontFace and BackFace tiles
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00 - STENCIL_KEEP : New value = Old Value
01 - STENCIL_ZERO : New value = 0
02 - STENCIL_ONES : New value = 8`hff
03 - STENCIL_REPLACE_TEST : New value = STENCIL_TEST_VAL
04 - STENCIL_REPLACE_OP : New value = STENCIL_OP_VAL
05 - STENCIL_ADD_CLAMP : New value = Old Value + STENCIL_OP_VAL (clamp)
06 - STENCIL_SUB_CLAMP : New value = Old Value - STENCIL_OP_VAL (clamp)
07 - STENCIL_INVERT : New value = ~Old value
08 - STENCIL_ADD_WRAP : New value = Old Value + STENCIL_OP_VAL (wrap)
09 - STENCIL_SUB_WRAP : New value = Old Value - STENCIL_OP_VAL (wrap)
10 - STENCIL_AND : New value = Old Value & STENCIL_OP_VAL
11 - STENCIL_OR : New value = Old Value | STENCIL_OP_VAL
12 - STENCIL_XOR : New value = Old Value ^ STENCIL_OP_VAL
13 - STENCIL_NAND : New value = ~(Old Value & STENCIL_OP_VAL)
14 - STENCIL_NOR : New value = ~(Old Value | STENCIL_OP_VAL)
15 - STENCIL_XNOR : New value = ~(Old Value ^ STENCIL_OP_VAL)
8 | DB: THE TILE AWAKENS | MAY 13, 2024 | CONFIDENTIAL
Tile Kill
DB_SC_TILE_MASK
DB_SC_TILE_TILE_RATE*
HZ_TK_HIZS INFO
TILE_KILL
TK_DF_HIZS INFO
TK_DF_FAST_Z_OP
TK_DF_FAST_STENCIL_OP
*Pixel Rate Tiles are what happen to Fast Tile Ops when color is on. The DB
still does its operations at tile rate instead of sample rate, but the DB tells the
SC to run its detail walker at 1xAA (pixel rate), therefore running the tile at
1xAA rates instead of the potentially slower AA sample rates.
9 | DB: THE TILE AWAKENS | MAY 13, 2024 | CONFIDENTIAL
Tile Kill
One flop stage at output, thus tk_db (output) <= hz_tk (input)
Output from hi_z_s_checker includes HiZS Info:
{ UNMAPPED S, UNMAPPED Z, MAY S UPDATE, MAY DB FAIL, MAY S FAIL, MAY Z FAIL, MAY Z PASS }
This can be used to accelerate QUAD operations:
Z Op Determination
FAST_NO_OP: If the Z test is known (either !MayZPass or !MayZFail), and it will not write (either !MayZPass or
Z writes disabled), then the Z Op is a NO-OP and can be run at tile rate since no work remains.
FAST_SET:
If the Z test is known to pass and will write to a fully covered tile (which also means
Alpha2Mask, etc. is not on as preprocessed away by the HiZ checker), then this tile’s Z op is a FAST_SET and
can run at tile rate.
SLOW_OP:
Otherwise, this tile either has Z tests being performed, or has Z writes being performed on a
per sample basis, which makes it a SLOW_OP.
Stencil Op Determination
FAST_NO_OP: If the stencil test is known (either !MaySFail or only MaySFail) or has no effect, and it will not
write stencil (!MayStecilUpdate), then the Stencil Op is a NO-OP and can be run at tile rate since no work
remains.
FAST_SET:
If the Stencil test is known or has no effect and all possible test outcomes will perform the
same stencil op which happens to be REPLACE or ZERO, then this tile’s Stencil op is a FAST_SET and can run at
tile rate.
CONST_OP: If the Stencil test is known or has no effect and all possible test outcomes will perform the
same stencil op which is not REPLACE or ZERO, then this tile’s Stencil op is a CONST_OP and can possibly run
at tile rate if the dest data is single stencil compressed. The Quad Op Pipe will determine this and compensate
accordingly later.
SLOW_OP:
Otherwise, this tile either has stencil tests being performed, or has stencil writes being
performed on a per sample basis, which makes it a SLOW_OP.
10 | DB: THE TILE AWAKENS | MAY 13, 2024 | CONFIDENTIAL
Questions?
11 | DB: THE TILE AWAKENS | MAY 13, 2024 | CONFIDENTIAL