diff --git a/libraries/AP_HAL_ChibiOS/hwdef/Pixhawk6C/hwdef.dat b/libraries/AP_HAL_ChibiOS/hwdef/Pixhawk6C/hwdef.dat
index 78eacecfd4..f0a16789bf 100644
--- a/libraries/AP_HAL_ChibiOS/hwdef/Pixhawk6C/hwdef.dat
+++ b/libraries/AP_HAL_ChibiOS/hwdef/Pixhawk6C/hwdef.dat
@@ -144,6 +144,12 @@ PD13 I2C4_SDA I2C4
 I2C_ORDER I2C4 I2C1 I2C2
 define HAL_I2C_INTERNAL_MASK 1
 
+# this board is tight on DMA channels. To allow for more UART DMA we
+# disable DMA on I2C. This also prevents a problem with DMA on I2C
+# interfering with IMUs
+NODMA I2C*
+define STM32_I2C_USE_DMA FALSE
+
 # heater
 PB9 HEATER_EN OUTPUT LOW GPIO(80)
 define HAL_HEATER_GPIO_PIN 80
@@ -215,9 +221,14 @@ define HAL_BARO_ALLOW_INIT_NO_BARO 1
 define HAL_PROBE_EXTERNAL_I2C_COMPASSES
 COMPASS IST8310 I2C:0:0x0C false ROTATION_NONE
 
+# compensate for magnetic field generated by the heater on 6C IST8310
+define HAL_HEATER_MAG_OFFSET {AP_HAL::Device::make_bus_id(AP_HAL::Device::BUS_TYPE_I2C,0,0xc,0xa),Vector3f(17,14,0)}
+
+
 # we need to stop the probe of an IST8310 as an internal compass with PITCH_180
 define HAL_COMPASS_DISABLE_IST8310_INTERNAL_PROBE
 
+
 # SPI devices
 SPIDEV bmi055_g SPI1 DEVID1  BMI055_G_CS  MODE3 10*MHZ 10*MHZ
 SPIDEV bmi055_a SPI1 DEVID2  BMI055_A_CS  MODE3 10*MHZ 10*MHZ