diff --git a/docs/src/man/man3/hm2_bspi_write_chan.3.adoc b/docs/src/man/man3/hm2_bspi_write_chan.3.adoc
index 066f5327f3d..46152f86a4b 100644
--- a/docs/src/man/man3/hm2_bspi_write_chan.3.adoc
+++ b/docs/src/man/man3/hm2_bspi_write_chan.3.adoc
@@ -33,7 +33,7 @@ Not available in non-realtime components.
 
 == RETURN VALUE
 
-Returns 0 on success and -1 on failure.
+Returns a positive value on success and -1 on failure.
 
 == SEE ALSO
 
diff --git a/src/hal/drivers/mesa-hostmot2/bspi.c b/src/hal/drivers/mesa-hostmot2/bspi.c
index c48493c9c83..7d3d043af10 100644
--- a/src/hal/drivers/mesa-hostmot2/bspi.c
+++ b/src/hal/drivers/mesa-hostmot2/bspi.c
@@ -121,6 +121,10 @@ int hm2_tram_add_bspi_frame(char *name, int chan, rtapi_u32 **wbuff, rtapi_u32 *
         HM2_ERR_NO_LL("Can not find BSPI instance %s.\n", name);
         return -1;
     }
+    if (chan < 0 || chan > 15) {
+        HM2_ERR("BSPI %s: channel number %i is out of range\n", name, chan);
+        return -1;
+    }
     if (hm2->bspi.instance[i].conf_flag[chan] != true){
         HM2_ERR("The selected write channel (%i) on bspi instance %s.\n" 
                 "Has not been configured.\n", chan, name);
@@ -187,8 +191,9 @@ int hm2_bspi_clear_fifo(char * name)
     }
     rtapi_u32 zero = 0;
     r = hm2->llio->write(hm2->llio, hm2->bspi.instance[i].count_addr, &zero, sizeof(rtapi_u32));
-    if (r < 0) {
+    if (!r) {
         HM2_ERR("BSPI: hm2->llio->write failure %s\n", name);
+        return -1;
     }
     
     return r;
@@ -205,14 +210,19 @@ int hm2_bspi_write_chan(char* name, int chan, rtapi_u32 val)
         HM2_ERR_NO_LL("Can not find BSPI instance %s.\n", name);
         return -1;
     }
+    if (chan < 0 || chan > 15) {
+        HM2_ERR("BSPI %s: channel number %i is out of range\n", name, chan);
+        return -1;
+    }
     if (hm2->bspi.instance[i].conf_flag[chan] != true){
         HM2_ERR("The selected write channel (%i) on bspi instance %s.\n" 
                 "Has not been configured.\n", chan, name);
         return -1;
     }
     r = hm2->llio->write(hm2->llio, hm2->bspi.instance[i].addr[chan], &buff, sizeof(rtapi_u32));
-    if (r < 0) {
+    if (!r) {
         HM2_ERR("BSPI: hm2->llio->write failure %s\n", name);
+        return -1;
     }
     
     return r;
@@ -247,6 +257,10 @@ int hm2_bspi_setup_chan(char *name, int chan, int cs, int bits, double mhz,
                 "BSPI only supports 1-64 bits\n", name, chan, bits);
         return -1;
     }
+    if (mhz <= 0) {
+        HM2_ERR("BSPI %s: clock frequency must be greater than zero\n", name);
+        return -1;
+    }
     if (delay < 0 || delay > 1e6){
         HM2_ERR("The requested frame delay on channel %i of %inS seems "
                 "rather implausible for an SPI device. Exiting.\n", delay, chan);
diff --git a/src/hal/drivers/mesa-hostmot2/inm.c b/src/hal/drivers/mesa-hostmot2/inm.c
index 596b9e2ba02..ecb935cf634 100644
--- a/src/hal/drivers/mesa-hostmot2/inm.c
+++ b/src/hal/drivers/mesa-hostmot2/inm.c
@@ -423,7 +423,21 @@ void hm2_inm_force_write(hostmot2_t *hm2) {
             scanrate = 10000000;
 	    hal_set_ui32(inst->hal.param.scan_rate, scanrate/inst->scanwidth);
         }
-        divisor = (hm2->inm.clock_frequency / (4 * scanrate)) - 1;
+        if (scanrate <= 0) {
+            divisor = 1023;
+            // Round up so the normalized rate stays within the divisor limit.
+            hal_set_ui32(inst->hal.param.scan_rate,
+                    (hm2->inm.clock_frequency - 1)
+                    / (4 * (divisor + 1) * inst->scanwidth) + 1);
+        } else {
+            divisor = (hm2->inm.clock_frequency / (4 * scanrate)) - 1;
+            if (divisor > 1023) {
+                divisor = 1023;
+                hal_set_ui32(inst->hal.param.scan_rate,
+                        (hm2->inm.clock_frequency - 1)
+                        / (4 * (divisor + 1) * inst->scanwidth) + 1);
+            }
+        }
         rtapi_u32 fast_scans = hal_get_ui32(inst->hal.param.fast_scans);
 	if (fast_scans > 63) {
             fast_scans = hal_set_ui32(inst->hal.param.fast_scans, 63);
@@ -472,13 +486,24 @@ void hm2_inm_write(hostmot2_t *hm2) {
 	    hal_set_ui32(inst->hal.param.scan_rate, scanrate/inst->scanwidth);
             HM2_ERR("inm %d scanrate too high, resetting to %d \n", i, hal_get_ui32(inst->hal.param.scan_rate));
         }
-        divisor = (hm2->inm.clock_frequency / (4 * scanrate)) - 1;
 //      bound divisor so we dont splatter into other fields
-	if ((divisor > 1023 ) | (scanrate == 0 )) {
+	if (scanrate <= 0) {
             divisor = 1023;
-	    hal_set_ui32(inst->hal.param.scan_rate, (hm2->inm.clock_frequency/4)/(divisor +1)
-            /inst->scanwidth);
+            // Round up so the normalized rate stays within the divisor limit.
+	    hal_set_ui32(inst->hal.param.scan_rate,
+                (hm2->inm.clock_frequency - 1)
+                / (4 * (divisor + 1) * inst->scanwidth) + 1);
             HM2_ERR("inm %d scanrate too low, resetting to %d \n", i, hal_get_ui32(inst->hal.param.scan_rate));
+        } else {
+            divisor = (hm2->inm.clock_frequency / (4 * scanrate)) - 1;
+	    if (divisor > 1023) {
+                divisor = 1023;
+	        hal_set_ui32(inst->hal.param.scan_rate,
+                    (hm2->inm.clock_frequency - 1)
+                    / (4 * (divisor + 1) * inst->scanwidth) + 1);
+                HM2_ERR("inm %d scanrate too low, resetting to %d \n",
+                        i, hal_get_ui32(inst->hal.param.scan_rate));
+            }
         }
         rtapi_u32 fast_scans = hal_get_ui32(inst->hal.param.fast_scans);
 	if (fast_scans > 63) {
diff --git a/src/hal/drivers/mesa-hostmot2/inmux.c b/src/hal/drivers/mesa-hostmot2/inmux.c
index eee23922016..833bea8907e 100644
--- a/src/hal/drivers/mesa-hostmot2/inmux.c
+++ b/src/hal/drivers/mesa-hostmot2/inmux.c
@@ -348,7 +348,21 @@ void hm2_inmux_force_write(hostmot2_t *hm2) {
             muxrate = 5000000;
 	    hal_set_ui32(inst->hal.param.scan_rate, muxrate/inst->scanwidth);
         }
-        divisor = (hm2->inmux.clock_frequency / (4 * muxrate)) - 1;
+        if (muxrate <= 0) {
+            divisor = 1023;
+            // Round up so the normalized rate stays within the divisor limit.
+            hal_set_ui32(inst->hal.param.scan_rate,
+                    (hm2->inmux.clock_frequency - 1)
+                    / (4 * (divisor + 1) * inst->scanwidth) + 1);
+        } else {
+            divisor = (hm2->inmux.clock_frequency / (4 * muxrate)) - 1;
+            if (divisor > 1023) {
+                divisor = 1023;
+                hal_set_ui32(inst->hal.param.scan_rate,
+                        (hm2->inmux.clock_frequency - 1)
+                        / (4 * (divisor + 1) * inst->scanwidth) + 1);
+            }
+        }
         rtapi_u32 fast_scans = hal_get_ui32(inst->hal.param.fast_scans);
 	if (fast_scans > 63) {
             fast_scans = hal_set_ui32(inst->hal.param.fast_scans, 63);
@@ -394,13 +408,24 @@ void hm2_inmux_write(hostmot2_t *hm2) {
 	    hal_set_ui32(inst->hal.param.scan_rate, muxrate/inst->scanwidth);
             HM2_ERR("InMux %d scanrate too high, resetting to %d \n", i, hal_get_ui32(inst->hal.param.scan_rate));
         }
-        divisor = (hm2->inmux.clock_frequency / (4 * muxrate)) - 1;
 //      bound divisor so we dont splatter into other fields
-	if ((divisor > 1023 ) | (muxrate == 0 )) {
+	if (muxrate <= 0) {
             divisor = 1023;
+            // Round up so the normalized rate stays within the divisor limit.
 	    hal_set_ui32(inst->hal.param.scan_rate,
-                (hm2->inmux.clock_frequency/4) / (divisor +1) / inst->scanwidth);
+                (hm2->inmux.clock_frequency - 1)
+                / (4 * (divisor + 1) * inst->scanwidth) + 1);
             HM2_ERR("InMux %d scanrate too low, resetting to %d \n", i, hal_get_ui32(inst->hal.param.scan_rate));
+        } else {
+            divisor = (hm2->inmux.clock_frequency / (4 * muxrate)) - 1;
+	    if (divisor > 1023) {
+                divisor = 1023;
+	        hal_set_ui32(inst->hal.param.scan_rate,
+                    (hm2->inmux.clock_frequency - 1)
+                    / (4 * (divisor + 1) * inst->scanwidth) + 1);
+                HM2_ERR("InMux %d scanrate too low, resetting to %d \n",
+                        i, hal_get_ui32(inst->hal.param.scan_rate));
+            }
         }
         rtapi_u32 fast_scans = hal_get_ui32(inst->hal.param.fast_scans);
 	if (fast_scans > 63) {
diff --git a/src/hal/drivers/mesa-hostmot2/pins.c b/src/hal/drivers/mesa-hostmot2/pins.c
index 46a1e8a2ec9..e64ffc79e5d 100644
--- a/src/hal/drivers/mesa-hostmot2/pins.c
+++ b/src/hal/drivers/mesa-hostmot2/pins.c
@@ -769,7 +769,7 @@ int hm2_read_pin_descriptors(hostmot2_t *hm2) {
         
         if (pin->port_num >= hm2->llio->num_ioport_connectors) {
             HM2_ERR("hm2_read_pin_descriptors: Calculated port number (%d) is "
-                    "invalid\n", pin->port_pin );
+                    "invalid\n", pin->port_num );
             return -EINVAL;
         }
         
@@ -894,7 +894,9 @@ void hm2_print_pin_usage(hostmot2_t *hm2) {
 
         char connector_pin_name[100];
 
-        if (hm2->llio->io_connector_pin_names == NULL) {
+        if (hm2->llio->io_connector_pin_names == NULL
+                || (unsigned)i >= (hm2->llio->num_ioport_connectors
+                    * hm2->llio->pins_per_connector)) {
             snprintf(connector_pin_name, sizeof(connector_pin_name), "%s-%02d", hm2->llio->ioport_connector_name[pin->port_num], pin->port_pin);
         } else {
             if (hm2->llio->io_connector_pin_names[i] == NULL) {
diff --git a/src/hal/drivers/mesa-hostmot2/resolver.c b/src/hal/drivers/mesa-hostmot2/resolver.c
index f8c3a064ac2..74df77a44e6 100644
--- a/src/hal/drivers/mesa-hostmot2/resolver.c
+++ b/src/hal/drivers/mesa-hostmot2/resolver.c
@@ -283,6 +283,12 @@ void hm2_resolver_process_tram_read(hostmot2_t *hm2, long period) {
     for (i = 0; i < hm2->resolver.num_resolvers; i ++) {
         
         res = &hm2->resolver.instance[i];
+        rtapi_u32 index_div = hal_get_ui32(res->hal.param.index_div);
+
+        if (index_div == 0) {
+            HM2_ERR("resolver.%02d.index-div == 0, bogus, setting to 1\n", i);
+            index_div = hal_set_ui32(res->hal.param.index_div, 1);
+        }
         
         scale = hal_get_real(res->hal.param.scale);
         
@@ -326,7 +332,6 @@ void hm2_resolver_process_tram_read(hostmot2_t *hm2, long period) {
         if ((res->old_reg > hm2->resolver.position_reg[i]) && (res->old_reg - hm2->resolver.position_reg[i] > 0x80000000)){
             res->index_cnts++;
             if (hal_get_bool(res->hal.pin.index_enable)){
-                rtapi_u32 index_div = hal_get_ui32(res->hal.param.index_div);
                 int r = (res->index_cnts % index_div);
                 if ((index_div  > 1 && r == 1) 
                  || (index_div == 1 && r == 0)){
@@ -337,7 +342,7 @@ void hm2_resolver_process_tram_read(hostmot2_t *hm2, long period) {
         }
         else if ((res->old_reg < hm2->resolver.position_reg[i]) && (hm2->resolver.position_reg[i] - res->old_reg > 0x80000000)){
             res->index_cnts--;
-            if (hal_get_bool(res->hal.pin.index_enable) && (res->index_cnts % hal_get_ui32(res->hal.param.index_div) == 0)){
+            if (hal_get_bool(res->hal.pin.index_enable) && (res->index_cnts % index_div == 0)){
                 res->offset = (res->accum - hm2->resolver.position_reg[i] + 0x100000000LL);
                 hal_set_bool(res->hal.pin.index_enable, 0);
             }
diff --git a/src/hal/drivers/mesa-hostmot2/spix_rpi3.c b/src/hal/drivers/mesa-hostmot2/spix_rpi3.c
index 3e700048af6..22b4b7336b0 100644
--- a/src/hal/drivers/mesa-hostmot2/spix_rpi3.c
+++ b/src/hal/drivers/mesa-hostmot2/spix_rpi3.c
@@ -850,8 +850,8 @@ static const spix_port_t *rpi3_open(int port, const spix_args_t *args)
 	if(!rpp->spiport) {
 		rpp->clkdivw = spi0_clkdiv_calc(spiclk_base, args->clkw);
 		rpp->clkdivr = spi0_clkdiv_calc(spiclk_base, args->clkr);
-		ccw = spiclk_base / rpp->clkdivw;
-		ccr = spiclk_base / rpp->clkdivr;
+		ccw = spiclk_base / (rpp->clkdivw ? rpp->clkdivw : 65536);
+		ccr = spiclk_base / (rpp->clkdivr ? rpp->clkdivr : 65536);
 	} else {
 		rpp->clkdivw = spi1_clkdiv_calc(spiclk_base, args->clkw);
 		rpp->clkdivr = spi1_clkdiv_calc(spiclk_base, args->clkr);
diff --git a/src/hal/drivers/mesa-hostmot2/tp_pwmgen.c b/src/hal/drivers/mesa-hostmot2/tp_pwmgen.c
index fd5fa57530d..396d6fa2abb 100644
--- a/src/hal/drivers/mesa-hostmot2/tp_pwmgen.c
+++ b/src/hal/drivers/mesa-hostmot2/tp_pwmgen.c
@@ -443,9 +443,9 @@ void hm2_tp_pwmgen_prepare_tram_write(hostmot2_t *hm2) {
         if (scaled_Avalue > 1.0) scaled_Avalue = 1.0;
         else if (scaled_Avalue < -1.0) scaled_Avalue = -1.0;
         if (scaled_Bvalue > 1.0) scaled_Bvalue = 1.0;
-        else if (scaled_Avalue < -1.0) scaled_Avalue = -1.0;
+        else if (scaled_Bvalue < -1.0) scaled_Bvalue = -1.0;
         if (scaled_Cvalue > 1.0) scaled_Cvalue = 1.0;
-        else if (scaled_Avalue < -1.0) scaled_Avalue = -1.0;
+        else if (scaled_Cvalue < -1.0) scaled_Cvalue = -1.0;
 
         // duty_cycle goes from 0.0 to 1.0, and needs to be puffed out to 10 bits
 
diff --git a/src/hal/drivers/mesa-hostmot2/uart.c b/src/hal/drivers/mesa-hostmot2/uart.c
index 0ca9ed6a5a5..1e0758545ec 100644
--- a/src/hal/drivers/mesa-hostmot2/uart.c
+++ b/src/hal/drivers/mesa-hostmot2/uart.c
@@ -139,7 +139,7 @@ int hm2_uart_setup(char *name, int bitrate, rtapi_s32 tx_mode, rtapi_s32 rx_mode
     hostmot2_t *hm2;
     hm2_uart_instance_t *inst = NULL;
     rtapi_u32 buff;
-    int i,r;
+    int i;
     
     i = hm2_get_uart(&hm2, name);
     if (i < 0){
@@ -149,33 +149,40 @@ int hm2_uart_setup(char *name, int bitrate, rtapi_s32 tx_mode, rtapi_s32 rx_mode
     inst = &hm2->uart.instance[i];
   
     buff = (rtapi_u32)((bitrate * 1048576.0)/inst->clock_freq); //20 bits in this version
-    r = 0;
     if (buff != inst->bitrate){
+        rtapi_u32 zero = 0;
+        inst->bitrate = 0; // A partial change invalidates both directions' cached rate.
+        if (hm2->llio->write(hm2->llio, inst->rx_bitrate_addr,
+                            &buff, sizeof(buff)) == 0) goto fail;
+        if (hm2->llio->write(hm2->llio, inst->tx_bitrate_addr,
+                            &buff, sizeof(buff)) == 0) goto fail;
+        // Clear faults and FIFOs before caching the new configuration.
+        if (hm2->llio->write(hm2->llio, inst->rx_mode_addr,
+                            &zero, sizeof(zero)) == 0) goto fail;
+        if (hm2->llio->write(hm2->llio, inst->rx_fifo_count_addr,
+                            &zero, sizeof(zero)) == 0) goto fail;
+        if (hm2->llio->write(hm2->llio, inst->tx_fifo_count_addr,
+                            &zero, sizeof(zero)) == 0) goto fail;
         inst->bitrate = buff;
-        r += hm2->llio->write(hm2->llio, inst->rx_bitrate_addr, &buff, sizeof(rtapi_u32));
-        r += hm2->llio->write(hm2->llio, inst->tx_bitrate_addr, &buff, sizeof(rtapi_u32));
-        buff = 0;
-        r += hm2->llio->write(hm2->llio, inst->rx_mode_addr, &buff, sizeof(rtapi_u32)); // clear faults
-        r += hm2->llio->write(hm2->llio, inst->rx_fifo_count_addr, &buff, sizeof(rtapi_u32)); // clear fifo
-        r += hm2->llio->write(hm2->llio, inst->tx_fifo_count_addr, &buff, sizeof(rtapi_u32)); // clear fifo
     }
     
     if (tx_mode >= 0) {
         buff = ((rtapi_u32)tx_mode) & 0x7f;
-        r += hm2->llio->write(hm2->llio, inst->tx_mode_addr, &buff, sizeof(rtapi_u32));
+        if (hm2->llio->write(hm2->llio, inst->tx_mode_addr,
+                            &buff, sizeof(buff)) == 0) goto fail;
     }
     
     if (rx_mode >= 0) {
         buff = ((rtapi_u32)rx_mode) & 0xff;
-        r += hm2->llio->write(hm2->llio, inst->rx_mode_addr, &buff, sizeof(rtapi_u32));
-    }
-        
-    if (r < 0) {
-        HM2_ERR("UART: hm2->llio->write failure %s\n", name);
-        return -1;
+        if (hm2->llio->write(hm2->llio, inst->rx_mode_addr,
+                            &buff, sizeof(buff)) == 0) goto fail;
     }
     
     return 0;
+
+fail:
+    HM2_ERR("UART: hm2->llio->write failure %s\n", name);
+    return -1;
 }
 
 
@@ -189,17 +196,20 @@ int hm2_uart_send(char *name,  unsigned char data[], int count)
     static int err_flag = 0;
     
     inst = hm2_get_uart(&hm2, name);
-    if (inst < 0 && !err_flag){
-        HM2_ERR_NO_LL("Can not find UART instance %s.\n", name);
+    if (inst < 0){
+        if (!err_flag)
+            HM2_ERR_NO_LL("Can not find UART instance %s.\n", name);
         err_flag = 1;
         return -1;
     }
-    if (hm2->uart.instance[inst].bitrate == 0 && !err_flag){
-        HM2_ERR("The selected UART instance %s.\n" 
-                "Has not been configured.\n", name);
+    if (hm2->uart.instance[inst].bitrate == 0){
+        if (!err_flag)
+            HM2_ERR("The selected UART instance %s.\n" 
+                    "Has not been configured.\n", name);
         err_flag = 1; // don't fill dmesg with junk. 
         return -1;
     }
+    if (count < 0) return -1;
     
     c = 0;
     err_flag = 0;
@@ -207,12 +217,12 @@ int hm2_uart_send(char *name,  unsigned char data[], int count)
         buff = (data[c] + 
                 (data[c+1] << 8) +
                 (data[c+2] << 16) +
-                (data[c+3] << 24));
+                ((rtapi_u32)data[c+3] << 24));
         r = hm2->llio->write(hm2->llio, hm2->uart.instance[inst].tx4_addr,
                              &buff, sizeof(rtapi_u32));
-        if (r < 0) {
+        if (!r) {
             HM2_ERR("UART WRITE: hm2->llio->write failure %s\n", name);
-            return r;
+            return -1;
         }
         c = c + 4;
     }
@@ -223,9 +233,9 @@ int hm2_uart_send(char *name,  unsigned char data[], int count)
             buff = data[c];
             r = hm2->llio->write(hm2->llio, hm2->uart.instance[inst].tx1_addr,
                                  &buff, sizeof(rtapi_u32));
-            if (r < 0){
+            if (!r){
                 HM2_ERR("UART WRITE: hm2->llio->write failure %s\n", name);
-                return r;
+                return -1;
             }else{
                 return c + 1;
             }
@@ -234,9 +244,9 @@ int hm2_uart_send(char *name,  unsigned char data[], int count)
                     (data[c+1] << 8));
             r = hm2->llio->write(hm2->llio, hm2->uart.instance[inst].tx2_addr,
                                  &buff, sizeof(rtapi_u32));
-            if (r < 0){
+            if (!r){
                 HM2_ERR("UART_WRITE: hm2->llio->write failure %s\n", name);
-                return r;
+                return -1;
             }else{
                 return c + 2;
             }
@@ -246,9 +256,9 @@ int hm2_uart_send(char *name,  unsigned char data[], int count)
                     (data[c+2] << 16));
             r = hm2->llio->write(hm2->llio, hm2->uart.instance[inst].tx3_addr,
                                  &buff, sizeof(rtapi_u32));
-            if (r < 0){
+            if (!r){
                 HM2_ERR("UART WRITE: hm2->llio->write failure %s\n", name);
-                return r;
+                return -1;
             }else{
                 return c + 3;
             }
@@ -286,6 +296,10 @@ int hm2_uart_read(char *name, unsigned char data[])
     
     r = hm2->llio->read(hm2->llio, hm2->uart.instance[inst].rx_fifo_count_addr,
                         &buff, sizeof(rtapi_u32));
+    if (!r) {
+        HM2_ERR("UART: hm2->llio->read failure %s\n", name);
+        return -1;
+    }
     
     count = buff & 0x1F; 
     c = 0;
@@ -293,9 +307,9 @@ int hm2_uart_read(char *name, unsigned char data[])
         r = hm2->llio->read(hm2->llio, hm2->uart.instance[inst].rx4_addr,
                             &buff, sizeof(rtapi_u32));
         
-        if (r < 0) {
+        if (!r) {
             HM2_ERR("UART: hm2->llio->read failure %s\n", name);
-            return r;
+            return -1;
         }
           
         data[c]   = (buff & 0x000000FF);
@@ -311,18 +325,18 @@ int hm2_uart_read(char *name, unsigned char data[])
         case 1:
             r = hm2->llio->read(hm2->llio, hm2->uart.instance[inst].rx1_addr,
                                 &buff, sizeof(rtapi_u32));
-            if (r < 0) {
+            if (!r) {
                 HM2_ERR("UART READ: hm2->llio->read failure %s\n", name);
-                return r;
+                return -1;
             }
             data[c]   = (buff & 0x000000FF);
             return c + 1;
         case 2:
             r = hm2->llio->read(hm2->llio, hm2->uart.instance[inst].rx2_addr,
                                 &buff, sizeof(rtapi_u32));
-            if (r < 0) {
+            if (!r) {
                 HM2_ERR("UART READ: hm2->llio->read failure %s\n", name);
-                return r;
+                return -1;
             }
             data[c]   = (buff & 0x000000FF);
             data[c+1] = (buff & 0x0000FF00) >> 8;
@@ -330,9 +344,9 @@ int hm2_uart_read(char *name, unsigned char data[])
         case 3:
             r = hm2->llio->read(hm2->llio, hm2->uart.instance[inst].rx3_addr,
                                 &buff, sizeof(rtapi_u32));
-            if (r < 0) {
+            if (!r) {
                 HM2_ERR("UART READ: hm2->llio->read failure %s\n", name);
-                return r;
+                return -1;
             }
             data[c]   = (buff & 0x000000FF);
             data[c+1] = (buff & 0x0000FF00) >> 8;