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rp2040: Avoid run-time divide in i2c.c

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Rework the code slightly to avoid an expensive software divide when
calculating the rate in i2c.c .

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>
This commit is contained in:
Kevin O'Connor
2026-03-22 13:16:09 -04:00
parent 0c2416ea7f
commit 9ebff0cc84
2 changed files with 8 additions and 6 deletions
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2
src/rp2040/Kconfig
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@@ -14,8 +14,6 @@ config RPXXXX_SELECT
select HAVE_GPIO_HARD_PWM
select HAVE_STEPPER_OPTIMIZED_BOTH_EDGE
select HAVE_BOOTLOADER_REQUEST
# Software divide needed on rp2040 for rate calculation in i2c.c
select HAVE_SOFTWARE_DIVIDE_REQUIRED if MACH_RP2040
config BOARD_DIRECTORY
string

12
src/rp2040/i2c.c
View File

@@ -101,10 +101,14 @@ i2c_setup(uint32_t bus, uint32_t rate, uint8_t addr)
// See `i2c_set_baudrate` in the Pico SDK `hardware_i2c/i2c.c` file
// for details on the calculations here.
if (rate > 1000000)
rate = 1000000; // Clamp the rate to 1Mbps
uint32_t period = (pclk + rate / 2) / rate;
uint32_t lcnt = period * 3 / 5;
uint32_t period;
if (rate >= 1000000)
period = DIV_ROUND_CLOSEST(pclk, 1000000);
else if (rate >= 400000)
period = DIV_ROUND_CLOSEST(pclk, 400000);
else
period = DIV_ROUND_CLOSEST(pclk, 100000);
uint32_t lcnt = DIV_ROUND_CLOSEST(period * ((3<<16) / 5), 1<<16); // 60%
uint32_t hcnt = period - lcnt;
uint32_t sda_tx_hold_count = ((pclk * 3) / 10000000) + 1;