ST STM32L4+ Series Reference Manual page 458

Chrom-GRC™ (GFXMMU)
A block is considered as valid i.e. physically mapped when
•
Line is enable
•
The block number is greater or equal to the first valid block
•
The block number is lower or equal to the last valid block
When the block is valid, the physical address generated is considered as correct.
If the result of the MMU evaluation is not valid, the write operations are ignored, and read
operations return the default 32-bit value stored in the default value (DV) field of the graphic
MMU default value register (GFXMMU_DVR).
Block offset address calculation within the buffer
The block number is added to the line offset to get the offset of the block within the physical
buffer.
As a consequence, the line offset stored in the LUT is given by the following formula:
Line offset = [(Number of visible blocks already used) - (1
with:
•
The maximum value for the line offset is when all the block of all the line are used. As
the consequence the line offset for the last line can be maximum:
1023 x 256 x 6 = 0x3F:F00x
•
The minimum value for the line offset is when the last block of the first line is the first
valid block: -255*16 = - 0xFFx i.e 0x3F:F01x
As the consequence the full range of the line offset entry of the LUT is used.
Carry is not taken into account as this stage to be able to perform negative offset
calculations (values from 0x3F:F01x to 0x3F:FFFx)
As the block offset is within a 4 MByte buffer, the address generated is 22-bit wide.
Block offset address calculation
Once the offset of the block within the buffer as been calculated, this value is added to the
offset of the block respective to the physical buffer base address.
The offset of the blocks are defined in registers as shown
The resulting address and the buffer offset address shall be on 23-bit.
The carry is taken into account to trigger address overflow. The carry is propagated to the
graphic MMU status register (GFXMMU_SR) to set the buffer x overflow flag (BxOF).
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Figure 42. Block validation/comparator implementation
Add[23:22]
pBuffer0Offset[22:4]
pBuffer1Offset[22:4]
pBuffer2Offset[22:4]
pBuffer3Offset[22:4]
RM0432 Rev 6
PBufferOffset
st
visible block)] x block size
pBufferOffset[22:4]
RM0432
MSv43803V1