ST STM32L4+ Series Reference Manual page 953

RM0432
where
•
t = line time;
L
•
t
HSA
•
t
HBP
•
t
HACT
is calculated as t
•
t
ESCCLK
register.
The VLPSIZE field can be compared directly with the size of the command to be transmitted
to determine if there is time to transmit the command.
Consider an example of a frame with 16.4 μs per line and assume an escape clock
frequency of 20 MHz and a Lane bit rate of 800 Mbits/s. In this case, it is possible to send
420 bits in escape mode (that is, 164 bits = 16.4 μs * 20 MHz / 2). Still, since it is the Vertical
Active region of the frame, take into consideration the HSA, HBP, and HACT timings apart
from the D-PHY protocol and PHY timings. The following assumptions are made:
• number of active lanes is 4;
•
Lane byte clock period (lanebyteclkperiod) is 10 ns (800 Mbits per Lane);
• escape clock period is 50 ns (DSI_CCR.TXECKDIV = 5);
•
D-PHY takes 180 ns to pass from Low-Power to High-Speed mode
(DSI_DLTCR.LP2HS_TIME = 18);
•
D-PHY takes 200 ns to pass from High-Speed to Low-Power mode
(DSI_DLTCR.HS2LP_TIME = 20);
•
t
HSA
•
t
HBP
•
t
HACT
•
video is transmitted in Non-Burst mode;
•
DSI Host is configured for four lanes.
In this example, consider that you send video in Non-Burst mode. The VLPSIZE is
calculated as follows:
VLPSIZE = (16.4 µs -(420 ns + 800 ns + 12.8 µs + 180 ns +200 ns +
(22 × 50 ns + 2 × 50 ns)) / (2 × 8 × 50 ns) = 1 byte
Only one byte can be transmitted in this period. A short packet (for example, generic short
write) requires a minimum of four bytes. Therefore, in this example, commands are not sent
in the VACT region.
If Burst mode is enabled, more time is available to transmit the commands in the VACT
region, because HACT is time compressed.
VLPSIZE = (16.4 µs - (420 ns + 800 ns + (1280 × 3 / 4 × 10 ns) + 180 ns + 200 ns +
(22 × 50 ns + 2 × 50 ns) / (2 × 8 × 50 ns) = 5 bytes
For Burst mode, the VLPSIZE is 5 bytes and then a 4-byte short packet can be sent.
Transmission of commands in different periods
The LPSIZE and VLPSIZE fields allow a simple comparison to determine if a command can
be transmitted in any of the BLLP periods.
DSI Host (DSIHOST) applied to STM32L4R9xx and STM32L4S9xx only
= time of the HSA pulse (DSI_VHSACR.HSA);
= time of Horizontal back porch (DSI_VHBPCR.HBP);
= time of Video active. For Burst mode, the Video active is time compressed and
= VPSIZE * Bytes_per_Pixel /Number_Lanes * t
HACT
= escape clock period as programmed in TXECKDIV field of the DSI_CCR
= 420 ns;
= 800 ns;
= 12800 ns to send 1280 pixel at 24 bpp;
RM0432 Rev 6
;
Lane_byte_clk
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